Search

Parenteral nutrition (PN) is associated with increased infectious risks due to impaired intestinal immunity. Although glucagon-like peptide-2 (GLP-2) enhances the gut barrier function, it is uncertain whether it improves mucosal immunologic barrier function. We hypothesized that injecting the PN mouse model with GLP-2 improved innate and acquired immunity, and prevented bacterial translocation. Forty-eight hours after venous cannulation, male Institute of Cancer Research mice were randomly divided into 3 groups based on their diet: chow with saline (n = 10), PN (n = 9), or PN + GLP-2 (30 μg bid per mouse, n = 10) provided for 5 days. Compared with chow, PN reduced interleukin (IL)-4 and IL-13 levels (P < .05, respectively), whereas, compared with PN alone, GLP-2 injection increased IL-4 and IL-13 levels (P < .05, respectively). Compared with chow, PN considerably suppressed, whereas GLP-2 improved, secretory phospholipase A2 and cryptdin-4 expression. PN, compared with chow, considerably decreased lysozyme and polymeric immunoglobulin receptor levels, whereas, compared with PN, GLP-2 significantly increased these protein levels (P < .01, respectively). In tissue and luminal samples, compared with chow, PN reduced secretory immunoglobulin A levels (P < .05), whereas, compared with PN alone, GLP-2 increased secretory immunoglobulin A levels (P < .05). Functionally, more bacterial translocation was observed in the PN group compared with the chow group (P < .001), and GLP-2 injection decreased bacterial translocation to chow levels (P < .05). In summary, GLP-2 treatment may improve intestinal innate and acquired immunity, and prevent bacterial translocation in mice on total parenteral nutrition.

Immunoglobulin G (IgG) is currently the most studied immunoglobin class and is frequently used in antibody therapeutics in which its beneficial effector functions are exploited. IgG is composed of two heavy chains and two light chains, forming the basic antibody monomeric unit. In contrast, immunoglobulin A (IgA) and immunoglobulin M (IgM) are usually assembled into dimers or pentamers with the contribution of joining (J)-chains, which bind to the secretory component (SC) of the polymeric Ig receptor (pIgR) and are transported to the mucosal surface. IgA and IgM play a pivotal role in various immune responses, especially in mucosal immunity. Due to their structural complexity, 3D structural study of these molecules at atomic scale has been slow. With the emergence of cryo-EM and X-ray crystallographic techniques and the growing interest in the structure-function relationships of IgA and IgM, atomic-scale structural information on IgA-Fc and IgM-Fc has been accumulating. Here, we examine the 3D structures of IgA and IgM, including the J-chain and SC. Disulfide bridging and N-glycosylation on these molecules are also summarized. With the increasing information of structure–function relationships, IgA- and IgM-based monoclonal antibodies will be an effective option in the therapeutic field.

The polymeric immunoglobulin receptor (pIgR) plays a pivotal role in mucosal immune response by transporting polymeric immunoglobulins onto the surface of mucosal epithelia to protect animals from invading pathogens. In this study, the full-length cDNA of pIgR was firstly cloned in Qihe crucian carp ( Carassius auratus ), hereafter designated as CapIgR , by using reverse transcription polymerase chain reaction and rapid amplification of cDNA ends. The molecular characterization and expression of CapIgR were investigated. The full-length cDNA sequence of CapIgR was composed of 1409 bp, which included a 112 bp 5ʹ-untranslated region (UTR), a 984 bp ORF, and a 313 bp 3ʹ-UTR, with a putative polyadenylation signal sequence AATAAA located upstream of the poly(A) tail. The deduced amino acid sequence indicated that CapIgR was a single-spanning transmembrane protein with 327 amino acids and possessed a signal peptide, an extracellular region containing two immunoglobulin-like domains, a transmembrane region, and an intracellular region. The mRNA expression levels of CapIgR were detected in different tissues of healthy C. auratus by quantitative real-time PCR, and the highest expression level was found in the liver. After Aeromonas hydrophila challenge, CapIgR expression was upregulated in different tissues at certain time points, and temporal expression changes of CapIgR fluctuated in a time-dependent manner. CapIgR exhibited rapid immune response to A. hydrophila challenge and played an important role in the immune defense of fish. These findings provided insights into the structure, function, and immune defense mechanism of CapIgR in C. auratus . This study can serve as a basis for developing disease control strategies in aquaculture.

Identification of significant changes in urinary peptides may enable improved understanding of molecular disease mechanisms. We aimed towards identifying urinary peptides associated with critical course of COVID-19 to yield hypotheses on molecular pathophysiological mechanisms in disease development. In this multicentre prospective study urine samples of PCR-confirmed COVID-19 patients were collected in different centres across Europe. The urinary peptidome of 53 patients at WHO stages 6-8 and 66 at WHO stages 1-3 COVID-19 disease was analysed using capillary electrophoresis coupled to mass spectrometry. 593 peptides were identified significantly affected by disease severity. These peptides were compared with changes associated with kidney disease or heart failure. Similarities with kidney disease were observed, indicating comparable molecular mechanisms. In contrast, convincing similarity to heart failure could not be detected. The data for the first time showed deregulation of CD99 and polymeric immunoglobulin receptor peptides and of known peptides associated with kidney disease, including collagen and alpha-1-antitrypsin. Peptidomic findings were in line with the pathophysiology of COVID-19. The clinical corollary is that COVID-19 induces specific inflammation of numerous tissues including endothelial lining. Restoring these changes, especially in CD99, PIGR and alpha-1-antitripsin, may represent a valid and effective therapeutic approach in COVID-19, targeting improvement of endothelial integrity. ispartof: PROTEOMICS vol:21 issue:20 ispartof: location:Germany status: published

The polymeric immunoglobulin receptor (pIgR) is one of the most vital components of mucosal immunity that plays a pivotal role in mediating transcytosis of polymeric immunoglobulin (pIg) on epithelial surfaces for protection against invading pathogens. Herein, we cloned the full-length cDNA of Pelodiscus sinensis pIgR, designated as P. sinensis pIgR, made of an open reading frame (ORF) of 1848 bp, molecular weight of 68.2 kDa and estimated isoelectric point of 7.00. The deduced P. sinensis pIgR sequence had a leader peptide, extracellular region containing four immunoglobulin-like domains (Ig like domains), transmembrane and intracellular regions comparable with other vertebrates. P. sinensis pIgR contained four Ig like domains that corresponded with mammalian D1, D3, D4 and D5 similar with reptile and avian Ig like domains. It had 40 potential phosphorylation sites, four putative N-glycosylation sites and several motifs resembling mammalian pIgR motifs. Phylogenetic analysis showed a close relationship between P. sinensis pIgR with avian and reptile pIgRs. P. sinensis pIgR basal levels were higher in the esophagus, small intestine and intestinnum crissum than in other organs of health turtles. Intragastric delivery of LPS and Aeromonassobria led to significant upregulation of P. sinensis pIgR in tissues of the gastrointestinal tract. A polyclonal anti- P. sinensis pIgR antibody produced in rabbit reacted with the recombinant P. sinensis pIgR protein expressed in Escherichia coli in Western blot. These studies demonstrate the existence and immune response of P. sinensis pIgR to stimulation in mucosal organs in Chinese soft-shelled turtles.

Secretory IgA (sIgA) and its transcytosis receptor, polymeric immunoglobulin receptor (pIgR), along with mucus, form the first lines of intestinal defense. Threonine (Thr) is a major component of intestinal mucins and IgA, which are highly secreted under lipopolysaccharide (LPS) induced inflammation. In the current study, the effect of Thr on the secretory immune system was determined in an ex vivo chicken ileal explant model. Results showed that a 2-hour Thr-deprivation of culture medium induced a compensatory increase in the mRNA expression of interleukin-8 (IL-8), mucin 2 (MUC2), and IgA during LPS challenge, and this increase was suppressed with Thr addition to the media (P ≤ 0.05), suggesting that Thr was required for mucin and IgA production after exposure to LPS. Similarly, a 2-hour culture of explants from birds fed a Thr adequate diet showed an increase in the mRNA abundance of IL-8, MUC2, and IgA with LPS treatment (P ≤ 0.003), which had a trend to be attenuated with Thr supplementation in the media (P ≤ 0.10). In contrast, explants from birds fed a Thr deficient diet had no response to LPS treatment. These results indicated that in vivo Thr deficiency induced impaired inflammatory and secretory immune responses in broiler chicks. Furthermore, our results revealed that induction of MUC2 and pIgR gene expression required nuclear factor-κB (NF-κB) activation. Additionally, IgA transcytosis may be dependent on extracellular-regulated protein kinase (ERK) activation, which may indirectly impact pIgR gene expression.

Probiotic bacteria are frequently used for prevention of bacterial infections of the gastrointestinal tract, but there are only limited studies on their efficacy against viral gut infections in animals. The aim of this study was to investigate the effect of probiotic Lactobacillus reuteri L26 BiocenolTM on the innate and adaptive immune responses in germ-free Balb/c mice, experimentally infected by porcine circovirus type 2 (PCV2), which confers immunosuppressive effect. A total of 30 six-week-old female mice were divided into 3 groups and animals in experimental group LPCV (n=10) were inoculated with L. reuteri L26, animals in the control group (C; n=10) and experimental group PCV (n=10) received sterile De Man-Rogosa-Sharpe broth for 7 days. Subsequently, mice from both experimental groups were infected with PCV2; however, mice in the control group received virus cultivation medium (mock). Virus load in faeces, ileum and mesenteric lymph nodes (MLN); as well as gene expression of selected cytokines, immunoglobulin A (IgA) and polymeric Ig receptor (PIgR) in the ileum, and percentage of CD8+, CD19+ and CD49b+CD8- cells in the MLN were evaluated. Our results showed that L. reuteri significantly decreased the amount of PCV2 in faeces and in the ileum, and up-regulated the gene expression of chemokines, interferon (IFN)-γ, IgA and PIgR in the ileum. Increased IFN-γ mRNA level was accompanied by higher proportion of natural killer cells and up-regulated IgA and PIgR gene expressions were in accordance with significantly higher percentage of CD19+ lymphocytes in the MLN. These findings indicate that probiotic L. reuteri has an antiviral effect on PCV2 in the intestine which is mediated by stimulation of local gut immune response.

Pneumococci are major causes of bacterial meningitis. Iovino et al. show that pneumococci invade the brain and pass the blood–brain barrier by interacting with the endothelial receptors pIgR and PECAM-1 recognizing the pneumococcal adhesin RrgA and PspC on the bacterial surface., Streptococcus pneumoniae is the main cause of bacterial meningitis, a life-threating disease with a high case fatality rate despite treatment with antibiotics. Pneumococci cause meningitis by invading the blood and penetrating the blood–brain barrier (BBB). Using stimulated emission depletion (STED) super-resolution microscopy of brain biopsies from patients who died of pneumococcal meningitis, we observe that pneumococci colocalize with the two BBB endothelial receptors: polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1). We show that the major adhesin of the pneumococcal pilus-1, RrgA, binds both receptors, whereas the choline binding protein PspC binds, but to a lower extent, only pIgR. Using a bacteremia-derived meningitis model and mutant mice, as well as antibodies against the two receptors, we prevent pneumococcal entry into the brain and meningitis development. By adding antibodies to antibiotic (ceftriaxone)-treated mice, we further reduce the bacterial burden in the brain. Our data suggest that inhibition of pIgR and PECAM-1 has the potential to prevent pneumococcal meningitis.

Deregulation of the immune system is believed to contribute to cancer malignancy, which has led to recent therapeutic breakthroughs facilitating antitumor immunity. In a malignant setting, immunoglobulin receptors, which are fundamental components of the human immune system, fulfill paradoxical roles in cancer pathogenesis. This study describes a previously unrecognized pro-oncogenic function of polymeric immunoglobulin receptor (pIgR) in the promotion of cell transformation and proliferation. Mechanistically, pIgR overexpression is associated with YES proto-oncogene 1, Src family tyrosine kinase (Yes) activation, which is required for pIgR-induced oncogenic growth. Specifically, pIgR activates the Yes-DNAX-activating protein of 12 kDa-spleen tyrosine kinase-Rac1/CDC42-MEK (extracellular signal-regulated kinase kinase)/ERK (extracellular signal-regulated kinase) cascade in an immunoreceptor tyrosine-based activating motif (ITAM)-dependent manner to promote cell transformation and tumor growth, although pIgR itself does not contain an ITAM sequence. Additionally, the combination of pIgR and phosphorylated Yes (p-Yes) levels serves as a prognostic biomarker for hepatitis B surface antigen–positive and early-stage hepatocellular carcinoma (HCC) patients. Moreover, pharmacological targeting of MEK/ERK or Yes represents a therapeutic option for the subgroup of patients with pIgR/p-Yes–positive HCC based on our results with both cancer cell-line–based xenografts and primary patient-derived xenografts. Conclusion: Our findings reveal the molecular mechanism by which pIgR promotes cancer malignancy, suggest the clinical potential of targeting this pathway in HCC, and provide new insight into the oncogenic role of immunoglobulin receptors. (Hepatology 2017;65:1948-1962).

Salivary IgA—a primary factor in local immunity of the oral cavity—plays an important role in maintaining local immune function in the oral cavity and prevent upper respiratory tract infections. Oral IgA levels are known to fluctuate in an exercise-dependent manner; thus, we investigated the effects of voluntary exercise on salivary IgA secretion in rats to better understand the mechanism by which this occurs. Six-week-old male Wistar rats were placed in individual cages with or without access to exercise wheels for three weeks. Notably, animals who engaged in voluntary exercise demonstrated significant increases in IgA concentration in saliva and submandibular gland tissue, as well as a markedly higher salivary IgA flow rate. Moreover, active rats also exhibited elevated polymeric Ig receptor (pIgR) mRNA expression in submandibular gland tissue. Collectively, these results suggest that voluntary exercise may increase salivary IgA concentration and boost immune function in the oral cavity.

Hefty structures of IgA and IgM complexesImmunoglobulin M (IgM) and IgA are antibody isotypes that can form higher-order secretory complexes (sIgM and sIgA), which allows them to effectively bind and neutralize antigens with low-affinity repetitive epitopes, such as those found on the surface of many bacteria and viruses. The assembly and transport of these molecules is also dependent on the joining chain (J-chain) and the polymeric immunoglobulin receptor (pIgR) secretory component (SC). The architecture of these complex, multimeric structures has remained elusive. Liet al.resolved cryo–electron microscopy structures of the sIgM-Fc pentamer in complex with the J-chain and SC. Using similar techniques, Kumaret al.visualized dimeric, tetrameric, and pentameric structures of secretory sIgA-Fc interacting with the J-chain and SC. Both groups report highly similar mechanisms wherein the J-chain serves as a template for antibody oligomerization. An unanticipated, amyloid-like assembly of the oligomerized structure is present in both cases, with the J-chain conferring asymmetry for pIgR binding and transcytosis. These studies may inform structure-based engineering of these molecules for future therapeutic purposes.Science, this issue p.1014, p.1008

Secretory IgA (SIgA) is widely held to be responsible for the defense of the mucosae against pathogenics and other potentially harmful agents. In this study, polymeric Ig receptor (pIgR) knockout mice, which lack secretory antibodies (SAb), were used to investigate the role of vaccine-elicited SAb in protection against gastrointestinal bacterial infections. An essential role for specific SAb in protection against Vibrio cholerae was evident from experiments showing that vaccinated pIgR(-/-) mice, but not vaccinated C57BL/6 mice, were susceptible to cholera toxin challenge. Vaccination of C57BL/6 mice with Salmonella typhimurium elicited strong antigen-specific, mucosal responses, which blocked in vitro invasion of epithelia. However, vaccinated C57BL/6 and pIgR(-/-) mice were equally resistant to challenge infection with virulent S. typhimurium. Finally, we investigated the importance of SIgA in protection against recurrent infections with Citrobacter rodentium. Although higher numbers of bacteria were detected early after challenge infection in feces of vaccinated pIgR(-/-) mice compared with vaccinated C57BL/6 mice, both mouse strains showed complete clearance after 9 days. These results suggested that, in immune animals, SIgA is crucial for the protection of gastrointestinal surfaces against secreted bacterial toxins, may inhibit early colonization by C. rodentium, but is not essential for protection against re-infection with S. typhimurium or C. rodentium.

Aim: To investigate the expression of polymeric immunoglobulin receptor (pIgR) in endometrial adenocarcinoma and the relationship between pIgR and the clinicopathological features of endometrial adenocarcinoma. To investigate the role of pIgR in the biological behavior of endometrial adenocarcinoma cell lines. Methods: First, the paraffin-embedded endometrial adenocarcinoma samples and clinicopathological data from the Chao-Yang Hospital were collected. Next, immunohistochemistry was conducted to test the expression of pIgR in endometrial adenocarcinoma; the correlations between pIgR and clinicopathological features were detected. Then, the expression of pIgR in the Ishikawa cells was interfered with short-interfering RNA (siRNA). Finally, the migration and proliferation abilities of Ishikawa cells were detected by transwell and CCK8 assays before and after interference. Results: pIgR had a high expression level and higher H-score in endometrial adenocarcinoma (P = 0.013) than in noncancerous tissues. There was no correlation between pIgR and the histopathological features of endometrial adenocarcinoma (P ≥ 0.418). The migration ability of Ishikawa cells was increased after interference with pIgR (P = 0.023). The proliferation of Ishikawa cells was not different between the untreated and siRNA215-treated groups (P = 0.967). Conclusion: PIgR may be a predictive biomarker of endometrial adenocarcinoma and a potential target protein for immunotherapy of endometrial adenocarcinoma.

Background The polymeric immunoglobulin receptor (pIgR) maintains the integrity of epithelial barriers by transporting polymeric antibodies and antigens through the epithelial mucosa into the lumen. In this study, we examined the role of pIgR in maintaining gut barrier integrity, which is important for the normal development in mice. Methods Cohorts of pIgR−/− mice and their wildtype controls were housed under Specific Pathogen Free (SPF) conditions and monitored for weight gain as an indicator of development over time. The general physiology of the gastrointestinal tract was analysed using immunohistochemistry in young (8–12 weeks of age) and aged mice (up to 18 months of age), and the observed immunopathology in pIgR−/− mice was further characterised using flow cytometry. Urinary metabolites were analysed using gas chromatography-mass spectrometry (GC-MS), which revealed changes in metabolites that correlated with age-related increase in gut permeability in pIgR−/− mice. Results We observed that pIgR−/− mice exhibited delayed growth, and this phenomenon is associated with low-grade gut inflammation that increased with ageing. The gross intraepithelial lymphocytic (IEL) infiltration characteristic of pIgR−/− mice was redefined as CD8α+αβ+ T cells, the majority of which expressed high levels of CD103 and CD69 consistent with tissue resident memory T cells (TRM). Comparison of the urinary metabolome between pIgR−/− and wild-type mice revealed key changes in urinary biomarkers fucose, glycine and Vitamin B5, suggestive of altered mucosal permeability. A significant increase in gut permeability was confirmed by analysing the site-specific uptake of sugar probes in different parts of the intestine. Conclusion Our data show that loss of the secretory antibody system in mice results in enhanced accumulation of inflammatory IELs in the gut, which likely reflects ongoing inflammation in reaction to gut microbiota or food antigens, leading to delayed growth in pIgR−/− mice. We demonstrate that this leads to the presence of a unique urinary metabolome profile, which may provide a biomarker for altered gut permeability. Electronic supplementary material The online version of this article (10.1186/s10020-019-0077-2) contains supplementary material, which is available to authorized users.

Viral entry into the host cell is the first step towards successful infection. Viral entry starts with virion attachment, and binding to receptors. Receptor binding viruses either directly release their genome into the cell, or enter cells through endocytosis. For DNA viruses and a few RNA viruses, the endocytosed viruses will transport from cytoplasm into the nucleus followed by gene expression. Receptors on the cell membrane play a crucial role in viral infection. Although several attachment factors, or candidate receptors, for the infection of white spot syndrome virus (WSSV) were identified in shrimp, the authentic entry receptors for WSSV infection and the intracellular signaling triggering by interaction of WSSV with receptors remain unclear. In the present study, a receptor for WSSV infection in kuruma shrimp, Marsupenaeus japonicus, was identified. It is a member of the immunoglobulin superfamily (IgSF) with a transmembrane region, and is similar to the vertebrate polymeric immunoglobulin receptor (pIgR); therefore, it was designated as a pIgR-like protein (MjpIgR for short). MjpIgR was detected in all tissues tested, and its expression was significantly induced by WSSV infection at the mRNA and protein levels. Knockdown of MjpIgR, and blocking MjpIgR with its antibody inhibited WSSV infection in shrimp and overexpression of MjpIgR facilitated the invasion of WSSV. Further analyses indicated that MjpIgR could independently render non-permissive cells susceptible to WSSV infection. The extracellular domain of MjpIgR interacts with envelope protein VP24 of WSSV and the intracellular domain interacts with calmodulin (MjCaM). MjpIgR was oligomerized and internalized following WSSV infection and the internalization was associated with endocytosis of WSSV. The viral internalization facilitating ability of MjpIgR could be blocked using chlorpromazine, an inhibitor of clathrin dependent endocytosis. Knockdown of Mjclathrin and its adaptor protein AP-2 also inhibited WSSV internalization. All the results indicated that MjpIgR-mediated WSSV endocytosis was clathrin dependent. The results suggested that MjpIgR is a WSSV receptor, and that WSSV enters shrimp cells via the pIgR-CaM-Clathrin endocytosis pathway., Author summary White Spot Syndrome Virus (WSSV) is one of the most virulent pathogens in shrimp farming. Several viral candidate receptors, or attachment factors were reported in previous studies, however, most of them are not authentic transmembrane proteins. In particular, the protein receptor(s) required the intracellular signaling triggering by interaction of WSSV with receptors remain unclear. In the present study, a polymeric immunoglobulin receptor (pIgR) like protein, a bona fide transmembrane receptor, was identified in kuruma shrimp, Marsupenaeus japonicus (MjpIgR for short). Knockdown of MjpIgR by RNA interference, and blocking it by its antibody prevented WSSV infection in shrimp and overexpression of MjpIgR facilitated the invasion of WSSV. Further study found that MjpIgR could independently render non-permissive cells susceptible to WSSV infection. The extracellular cellular domain of MjpIgR interacts with envelope protein VP24 of WSSV and the intracellular domain interacts with calmodulin (MjCaM). MjpIgR was oligomerized and internalized following WSSV infection and the internalization was associated with endocytosis of WSSV. The viral internalization facilitating ability of MjpIgR could be blocked using chlorpromazine, an inhibitor of clathrin dependent endocytosis, indicating that MjpIgR-mediated WSSV endocytosis was clathrin dependent. The results suggested that MjpIgR is a WSSV receptor, and that WSSV enters shrimp cells via the pIgR-CaM-Clathrin endocytosis pathway. This study provides a new target for WSSV control in shrimp aquaculture.

Escherichia coliO157:H7 is the most well-studied serotype of enterohemorrhagicE. coli(EHEC) class ofE. coliintestinal pathogens, and is responsible for many outbreaks of serious food-borne illness worldwide each year. Adherence mechanisms are a critical component of its pathogenesis, persistence in natural reservoirs, and environmental contamination.E. coliO157:H7 has a highly effective virulence operon, the Locus of Enterocyte Effacement (LEE), and its encoded intimate adherence mechanism is well characterized. However, factors involved in the preceding initial attachment are not well understood. In this study, we propose a mechanism of initial adherence used byE. coliO157:H7in vitro. We describe a bacterial protein not previously reported to be involved in adherence, Slp, and its interactions with the human host protein polymeric immunoglobulin receptor (pIgR). The human pIgR has previously been shown to act as an adherence receptor for some mucosal pathogens, and is highly expressed in the intestine. Following observation of significant colocalization betweenE. coliO157:H7 and pIgR location on Caco-2 cells, a co-immunoprecipitation (Co-IP) assay using a human recombinant Fc-tagged pIgR protein led to the identification of this protein. Disruption of Slp expression inE. coliO157:H7, through deletion of its encoding geneslp, produced a significant adherence deficiency to Caco-2 cells at early time points associated with initial adherence. Plasmid complementation ofslpfully restored the wild-type phenotype. Furthermore, immunofluorescence microscopy revealed evidence that this interaction is specific to the pathogenic strains ofE. colitested, and not the nonpathogenic strain E. coli K12. Additionally, deletion ofslpresulted in the absence of the corresponding protein band in further Co-IP assays, while the plasmid-encodedslpcomplementation of the deletion mutant strain restored the wild-type pattern. These data support the proposal that Slp directly contributes to initial adherence, with the pIgR protein as its proposed receptor.Author summaryEscherichia coliO157:H7 and other enterohemorrhagicE. coli(EHEC) are responsible for tens of thousands of cases of food-borne illness in the United States each year.E. coliO157:H7 has a particularly effective intimate adherence mechanism. However, the mechanisms of initial adherence, which facilitate attachment and virulence prior to the engagement of intimate adherence, are not well understood. In this study, we describe an initial adherence interaction between theE. coliO157:H7 Slp and the human polymeric immunoglobulin receptor (pIgR) expressed by the human colonic epithelial cell line Caco-2. The relationship was first demonstrated as a significant colocalization between the locations ofE. coliO157:H7 bacterial cells and pIgR protein using immunofluorescence microscopy. TheE. coliO157:H7 Slp protein was identified, and disruption of theslpgene resulted in a severe adherence deficiency to Caco-2 cells during initial adherence. This effect was reversed upon complementation of the Δslpstrain with a plasmid-encodedslpgene, and the constitutive over-expression ofslpresulted in hyper-adherence exceeding that of the wild-typeE. coliO157:H7. These data support the proposition that Slp directly contributes to initial adherence, with the pIgR protein as its proposed receptor.

The polymeric Ig receptor (PIgR) constitutes an important part of the immune system by mediating transcytosis of dimeric IgA into mucosal fluids. Although well studied in organs such as the intestine, the regulation and localization of PIgR in human kidney are incompletely characterized. Herein, using immunohistochemistry, we show that in healthy human kidneys, PIgR is expressed by the progenitor-like tubular scattered cells of the proximal tubules and by parietal epithelial cells of glomeruli. We further show that proximal tubular expression of PIgR becomes widespread during kidney disease, correlating to elevated levels of urinary secretory IgA. Urinary secretory IgA levels also correlated to the degree of tubular fibrosis, plasma creatinine, and urea levels. In addition, primary tubular cells were cultured to study the function and regulation of PIgR in vitro. Cellular PIgR expression was induced by conditioned medium from activated human leukocytes, as well as by inflammatory cytokines, whereas transforming growth factor-β1 caused decreased expression. Furthermore, interferon-γ increased the transcytosis of dimeric IgA in cultured tubular cells. Finally, a correlation study of mRNA data from the Genotype-Tissue Expression portal indicated that PIGR mRNA expression in kidney correlates to the expression of TNFSF13, a cytokine involved in plasma cell class switching to IgA. These results indicate that PIgR induction is an integral part of the injury phenotype of renal tubular cells.

The Polymeric Immunoglobulin Receptor (pIgR) gene has been proved to play an important role in transporting polymeric immunoglobulin (Ig) in the mucosal tissues of mammals. pIgR gene also exists in teleost, but the genetic diversity and functions of this gene still need to be further explored. We obtained seven grass carp pIgR splicing transcripts, a full-length pIgR (CipIgR-1) and six truncated variants (CipIgR-2 to CipIgR-7). The full-length pIgR contained two immunoglobulin-like domains (ILD), a transmembrane domain (TMD) and a cytoplasmic domain (CyD). The CipIgR-2 lacked a small part in CyD, and CipIgR-3 lost TMD and CyD. Partial cDNA sequences of the other four grass carp pIgR variants (CipIgR-4 to CipIgR-7) were also cloned. The total expression levels of CipIgR and its variants in different tissues were detected by real-time quantitative PCR. The highest expression was found in the intestine, followed by the spleen and the skin. The function of the two extracellular ILDs of CipIgR was investigated based on its combining capacity with grass carp immunoglobulin M (IgM) and aquatic pathogenic bacteria. The cDNA sequences of two ILDs were cloned and expressed in Escherichia coli BL21 (DE3). Recombinant ILDs protein was purified and incubated with different bacteria respectively. Results of Western blot showed the recombinant protein could combine Bacillus subtilis, Vibrio parahaemolyticus, and Escherichia coli. In addition, binding activity of rILDs with grass carp IgM was detected. Collectively, these results indicated that multiple variants of pIgR gene in grass carp might be involved in the antibacterial immunity.

Melanoma patients with a single microscopically-positive sentinel lymph node (SLN) are classified as stage III and are often advised to undergo expensive and substantially toxic adjuvant therapy. However, the 5-year survival rate for these patients, with or without adjuvant therapy, varies from 14 to 85 %, representing a heterogeneous biological population with a variable prognosis. We aimed to identify an SLN gene signature to aid in risk stratification of patients with tumor-positive SLNs. Microarray experiments were performed to screen SLN genes in recurrence (N = 39) versus non-recurrence (N = 58) groups in the training dataset. Quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) assay was applied to confirm the expression of selected SLN genes, which were further verified using an independent validation cohort (N = 30). Area under the receiver operating characteristic curve (AUC) was calculated to evaluate prognostic accuracy of the selected SLN gene panel, and the prognostic value of our SLN gene signature was also compared with the current American Joint Committee on Cancer (AJCC) staging system. We identified two SLN genes (PIGR and TFAP2A) that provided high prognostic accuracy in SLN-positive melanoma patients (AUC = 0.864). These two SLN genes, along with clinicopathological features, can differentiate the high- and low-risk groups in node-positive melanoma patients in this cohort. The two SLN genes, when combined with clinicopathological features, may offer a new tool for personalized patient risk assessment.

Background: Pancreatic ductal adenocarcinoma (PDAC) remains a devastating disease due to the lack of specific early diagnostic markers. To improve the outcomes, proteomic approaches are being developed for the discovery of novel biomarkers of PDAC. Methods: Using tandem mass tag labelling and LC-MS/MS, we performed comparative analyses of pre- and postoperative sera from PDAC patients to identify specific serum biomarkers for PDAC. In validation studies, we evaluated the discriminatory power of candidate proteins. Results: Among the 302 proteins analysed, 20 were identified as potential biomarkers, with C4b-binding protein α-chain (C4BPA) and polymeric immunoglobulin receptor (PIGR) being selected for further analysis. The sera levels of C4BPA and PIGR were significantly higher in the preoperative PDAC patients than in the postoperative ones (P

Although several new biomarkers have been recently proposed for psoriasis (Ps) and psoriasis arthritis (PsA), nothing is known about their diagnostic sensitivity and specificity, and their routine use. We therefore searched in-depth for new biomarker candidates using a biobank with EDTA-plasma from 158 individuals, patients and healthy controls. Samples from 6 selected pairs (patients against healthy controls) were searched proteomically using a workflow of extensive and precise design that is highly comprehensive. Subsequent verification was performed using ELISA and the entire biobank. By proteomic methods, 208 altered proteins were identified. Of these, 15 biomarker candidates were selected for verification. Of these 15, 4 individual parameters and 11 combinations significantly discriminated between patient and control groups. These individual parameters were Zn-α2-glycoprotein, complement C3, polymeric immunoglobulin receptor, and plasma kallikrein. Significant discrimination was obtained by combinations of 2 or 3 parameters. One combination seemed suitable for diagnosing PsA. Moreover, several candidates desmoplakin, complement C3, polymeric immunoglobulin receptor, and cytokeratin 17, correlated with PASI in all patients. This first comprehensive proteomic study on non-depleted plasma identified several biomarker candidates that have not been described before as well as some known from previous studies. Biological significance Our non-gel proteomic analysis is based on the highly comprehensive and significantly optimized chromatographic protein pre-fractionation. The method allows a biomarker search in non-depleted plasma. The subsequent verification by ELISA identifies several biomarker-candidates for the unbiased diagnosis of psoriasis and psoriasis arthritis. Four of the identified candidate markers might be used individually. Combinations of several parameters improve the diagnostic sensitivity and specificity. The still not validated candidates form a reserve for further evaluation. Moreover, mass spectrometric data uncover several biomarker-candidates which show diverse protein species of the same protein with opposing changes in the same sample.

Mechanisms driving persistent airway inflammation in chronic obstructive pulmonary disease (COPD) are incompletely understood. As secretory immunoglobulin A (SIgA) deficiency in small airways has been reported in COPD patients, we hypothesized that immunobarrier dysfunction resulting from reduced SIgA contributes to chronic airway inflammation and disease progression. Here we show that polymeric immunoglobulin receptor-deficient (pIgR−/−) mice, which lack SIgA, spontaneously develop COPD-like pathology as they age. Progressive airway wall remodelling and emphysema in pIgR−/− mice are associated with an altered lung microbiome, bacterial invasion of the airway epithelium, NF-κB activation, leukocyte infiltration and increased expression of matrix metalloproteinase-12 and neutrophil elastase. Re-derivation of pIgR−/− mice in germ-free conditions or treatment with the anti-inflammatory phosphodiesterase-4 inhibitor roflumilast prevents COPD-like lung inflammation and remodelling. These findings show that pIgR/SIgA deficiency in the airways leads to persistent activation of innate immune responses to resident lung microbiota, driving progressive small airway remodelling and emphysema., The mechanisms driving lung inflammation and remodelling in chronic obstructive pulmonary disease (COPD) are incompletely understood. Here the authors show that lack of secretory IgA promotes bacterial invasion in small airways, resulting in leukocyte recruitment and a COPD-like phenotype.

Polymeric immunoglobulin receptors (pIgR) and neonatal Fc receptors (FcRn) are crucial immunoglobulin (Ig) receptors for the transcytosis of immunoglobulins, that is IgA, IgM and IgG, the levels of which in mucosal secretions were altered in both HIV- and SIV-infected individuals. To gain an insight into the changes of pIgR and FcRn expression after immunodeficiency virus (SHIV/SIV) infection, real-time RT-PCR methods were established and the mRNA levels of pIgR and FcRn in normal and SHIV/SIV-infected rhesus macaques were quantitatively examined. It was found that the levels of pIgR mRNA were within a range of 10(7) copies per million copies of GAPDH mRNA in the gut mucosa of rhesus macaques, which were up to 55 times higher than that in the oral mucosa, the highest among the non-gut tissues examined. Levels of FcRn mRNA were generally lower than that of pIgR, and the levels of FcRn mRNA in the gut mucosa were also lower than that in most non-gut tissues examined. Notably, the levels of pIgR mRNA in the duodenal mucosa were positively correlated with that of IL-17A in normal rhesus macaques. Both pIgR and FcRn mRNA levels were significantly reduced in the duodenal mucosa during acute SHIV infection and in the jejunum and caecum during chronic SHIV/SIV infection. These data expanded our knowledge on the expression of pIgR and FcRn in the gastrointestinal tract of rhesus macaques and demonstrated altered expression of pIgR and FcRn in SHIV/SIV, and by extension HIV infections, which might have contributed to HIV/AIDS pathogenesis.

Polymeric immunoglobulin receptor (pIgR) is a key component of the mucosal immune system that mediates epithelial transcytosis of immunoglobulins. The expression of pIgR was reported to be up-regulated and related to the prognosis of several human cancers. However, the clinical significance of pIgR in nasopharyngeal carcinoma (NPC) remains unclear. The purpose of this study was to detect the pIgR expression and its prognostic value in NPC. The expression of serum pIgR was measured in NPC patients and healthy controls by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and western blotting analyses. The relationship between its expression and clinical factors was analyzed by chi-square test. Then, the overall survival of patients was assessed by Kaplan-Meier analysis while the prognostic value of serum pIgR was estimated using univariate and multivariate analyses with cox regression analysis. Serum pIgR was down-regulated in NPC patients compared to that in healthy controls both at messenger RNA (mRNA) and protein levels. Especially, its expression was also significantly lower in patients at advantage stages (III-IV) than those at early stages (I-II). And, the low pIgR expression was strongly associated with advanced clinical stages, T stage, N stage, and distant metastasis. Kaplan-Meier analysis demonstrated that patients with low pIgR expression had a significantly shorter overall survival than those with high expression at any stages. Cox regression analysis suggested that pIgR was closely related to the prognosis of NPC. Serum pIgR expression was reduced in NPC, and it could be an independent prognostic predictor for patients with this cancer.

Dengue is a major global disease requiring improved treatment and prevention strategies. The recently licensed Sanofi-Pasteur Denvaxia vaccine does not protect children under the age of nine and additional vaccine strategies are thus needed to halt this expanding global epidemic. Here, we employed a molecular engineering approach and plant-expression to produce a humanised and highly immunogenic Poly-Immunoglobulin G Scaffold (PIGS) fused to the consensus dengue envelope protein III domain (cEDIII). The immunogenicity of this IgG Fc receptor targeted vaccine candidate was demonstrated in transgenic mice expressing human FcγRI/CD64, by induction of neutralising antibodies and evidence of cell-mediated immunity. Furthermore, these molecules were able to prime immune cells from human adenoid/tonsillar tissue ex vivo as evidenced by antigen-specific CD4+ and CD8+ T cell proliferation, IFN-γ and antibody production. The purified polymeric fraction of dengue PIGS (D-PIGS) induced stronger immune activation than the monomeric form, suggesting a more efficient interaction with the low affinity Fcγ receptors on antigen-presenting cells. These results show that the plant-expressed D-PIGS have the potential for translation towards a safe and easily scalable single antigen based tetravalent dengue vaccine. This article is protected by copyright. All rights reserved.

BACKGROUND:Polymeric immunoglobulin receptor (pIgR) transport of secretory immunoglobulin A (SIgA) to mucosal surfaces is thought to promote gut integrity and immunity to Salmonella enterica serovar Typhimurium (S. Typhimurium), an invasive pathogen in mice. To elucidate potential mechanisms, we assessed intestinal barrier function and both oral and systemic S. Typhimurium virulence in pIgR knockout (KO) and wildtype (WT) mice. METHODS:In uninfected animals, we harvested jejunal segments for Ussing chamber analyses of transepithelial resistance (TER); mesenteric lymph nodes (mLN) for bacterial culture; and serum and stool for IgA. Separately, we infected mice either orally or intravenously (IV) with S. Typhimurium to compare colonization, tissue dynamics, and inflammation between KOs and WTs. RESULTS:Uninfected KOs displayed decreased TER and dramatically increased serum IgA and decreased fecal IgA vs. WT; however, KO mLNs yielded fewer bacterial counts. Remarkably, WTs challenged orally with S. Typhimurium exhibited increased splenomegaly, tissue colonization, and pro-inflammatory cytokines vs. pIgR KOs, which showed increased survival following either oral or IV infection. CONCLUSIONS:Absence of pIgR compromises gut integrity but does not exacerbate bacterial translocation nor S. Typhimurium infection. These findings raise the possibility that immune adaptation to increased gut permeability and elevated serum IgA in the setting of SIgA deficiency provides compensatory protection against invasive gut pathogens.

Noroviruses are enteric pathogens causing significant morbidity, mortality, and economic losses worldwide. Secretory immunoglobulins (sIg) are a first line of mucosal defense against enteric pathogens. They are secreted into the intestinal lumen via the polymeric immunoglobulin receptor (pIgR), where they bind to antigens. However, whether natural sIg protect against norovirus infection remains unknown. To determine if natural sIg alter murine norovirus (MNV) pathogenesis, we infected pIgR knockout (KO) mice, which lack sIg in mucosal secretions. Acute MNV infection was significantly reduced in pIgR KO mice compared to controls, despite increased MNV target cells in the Peyer's patch. Natural sIg did not alter MNV binding to the follicle-associated epithelium (FAE) or crossing of the FAE into the lymphoid follicle. Instead, naive pIgR KO mice had enhanced levels of the antiviral inflammatory molecules interferon gamma (IFN-γ) and inducible nitric oxide synthase (iNOS) in the ileum compared to controls. Strikingly, depletion of the intestinal microbiota in pIgR KO and control mice resulted in comparable IFN-γ and iNOS levels, as well as MNV infectious titers. IFN-γ treatment of wild-type (WT) mice and neutralization of IFN-γ in pIgR KO mice modulated MNV titers, implicating the antiviral cytokine in the phenotype. Reduced gastrointestinal infection in pIgR KO mice was also observed with another enteric virus, reovirus. Collectively, our findings suggest that natural sIg are not protective during enteric virus infection, but rather, that sIg promote enteric viral infection through alterations in microbial immune responses. IMPORTANCE Enteric virus, such as norovirus, infections cause significant morbidity and mortality worldwide. However, direct antiviral infection prevention strategies are limited. Blocking host entry and initiation of infection provides an established avenue for intervention. Here, we investigated the role of the polymeric immunoglobulin receptor (pIgR)-secretory immunoglobulin (sIg) cycle during enteric virus infections. The innate immune functions of sIg (agglutination, immune exclusion, neutralization, and expulsion) were not required during control of acute murine norovirus (MNV) infection. Instead, lack of pIgR resulted in increased IFN-γ levels, which contributed to reduced MNV titers. Another enteric virus, reovirus, also showed decreased infection in pIgR KO mice. Collectively, our data point to a model in which sIg-mediated microbial sensing promotes norovirus and reovirus infection. These data provide the first evidence of the proviral role of natural sIg during enteric virus infections and provide another example of how intestinal bacterial communities indirectly influence MNV pathogenesis.

The gastrointestinal tract houses millions of microbes, and thus has evolved several host defense mechanisms to keep them at bay, and prevent their entry into the host. One such mucosal surface defense is the secretion of secretory immunoglobulins (SIg). Secretion of SIg depends on the polymeric immunoglobulin receptor (pIgR), which transports polymeric Ig (IgA or IgM) from the basolateral surface of the epithelium to the apical side. Upon reaching the luminal side, a portion of pIgR, called secretory component (SC) is cleaved off to release Ig, forming SIg. Through antigen-specific and non-specific binding, SIg can modulate microbial communities and pathogenic microbes via several mechanisms: agglutination and exclusion from the epithelial surface, neutralization, or via host immunity and complement activation. Given the crucial role of SIg as a microbial scavenger, some pathogens also evolved ways to modulate and utilize pIgR and SIg to facilitate infection. This review will cover the regulation of the pIgR/SIg cycle, mechanisms of SIg-mediated mucosal protection as well as pathogen utilization of SIg.

Background Pneumococci are the major cause of bacterial meningitis globally. To cause meningitis pneumococci interact with the 2 endothelial receptors, polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1), to penetrate the blood-brain barrier (BBB) and invade the brain. Methods C57BL/6 mice were infected intravenously with bioluminescent pneumococci, and treated with ceftriaxone (1 hour postinfection) and anti-pIgR and PECAM-1 antibodies (1 or 5 hours postinfection), then monitored for 5 and 10 days. Bacterial brain invasion was analyzed using IVIS imaging and bacterial counts. Results Ceftriaxone, given early after pneumococcal challenge, cleared pneumococci from the blood but not from the brain. After combining ceftriaxone with receptor blockade, using anti-pIgR and PECAM-1 antibodies, we found 100% survival after 5 and 10 days of infection, in contrast to 60% for ceftriaxone alone. Combined antibiotic and antibody treatment resulted in no or few viable bacteria in the brain and no microglia activation. Antibodies remained bound to the receptors during the study period. Receptor blockade did not interfere with antibiotic permeability through the BBB. Conclusions We suggest that adjunct treatment with pIgR and PECAM-1 antibodies to antibiotics may prevent pneumococcal meningitis development and associated brain damages. However, further evaluations are required.

Polymeric immunoglobulin receptor (pIgR) plays an important role in mucosal immune systems. Secretory immunoglobulin A, composed of secretory component of pIgR and a dimeric form of immunoglobulin A, is secreted on mucosal surfaces and serves as a biological defense factor. pIgR gene expression is reportedly induced by activation of the transcription factor nuclear factor (NF)-κB. On the other hand, secretory leukocyte protease inhibitor (SLPI) is a glycoprotein that functions as a serine protease inhibitor. In alveolar epithelial cells, SLPI increases the level of IκBβ, which indicates that it is an inhibitor of NF-κB at the protein level. Taken together, SLPI may regulate pIgR expression; however, the specific mechanism by which this occurs is unclear. Therefore, the aim of this study was to elucidatethe influence of SLPI on pIgR expression.SLPI and pIgR localized in goblet cells and ciliated epithelial cells of the gastrointestinal tract, respectively. No cells were detected in which SLPI and pIgR were co-expressed. In addition, recombinant human SLPI stimulation of an epithelial cell line (HT-29) decreased the pIgR expression. The pIgR expression was also higher in SLPI-deficient Ca9-22 cells than in wild-type Ca9-22 cells. Furthermore, a luciferase assay using a NF-κB reporter plasmid and real-time RT-PCR analysis indicated that when SLPI was present, the transcriptional activity of NF-κB protein was suppressed, which was accompanied by anincrease in the protein, but not the mRNA,expression of IκBβ. These results demonstrate that SLPI down-regulates pIgR expression through the NF-κB signaling pathway by inhibiting degradation of IκBβ protein.

To clarify the effect of secretory IgA (sIgA) deficiency on gut homeostasis, we examined intraepithelial lymphocytes (IELs) in the small intestine (SI) of polymeric immunoglobulin receptor-deficient (pIgR(-/-) ) mice. The pIgR(-/-) mice exhibited the accumulation of CD8αβ(+) T-cell receptor (TCR)-αβ(+) IELs (CD8αβ(+) αβ-IELs) after weaning, but no increase of CD8αβ(+) γδ-IELs was detected in pIgR(-/-) TCR-β(-/-) mice compared with pIgR(+/+) TCR-β(-/-) mice. When 5-bromo-2'-deoxyuridine (BrdU) was given for 14 days, the proportion of BrdU-labelled cells in SI-IELs was not different between pIgR(+/+) mice and pIgR(-/-) mice. However, the proportion of BrdU-labelled CD8αβ(+) -IELs became higher in pIgR(-/-) mice than pIgR(+/+) mice 10 days after discontinuing BrdU-labelling. Intravenously transferred splenic T cells migrated into the intraepithelial compartments of pIgR(+/+) TCR-β(-/-) mice and pIgR(-/-) TCR-β(-/-) mice to a similar extent. In contrast, in the case of injection of immature bone marrow cells, CD8αβ(+) αβ-IELs increased much more in the SI of pIgR(-/-) TCR-β(-/-) mice than pIgR(+/+) TCR-β(-/-) mice 8 weeks after the transfer. αβ-IELs from pIgR(-/-) mice could produce more interferon-γ and interleukin-17 than those of pIgR(+/+) mice, and intestinal permeability tended to increase in the SI of pIgR(-/-) mice with aging. Taken together, these results indicate that activated CD8αβ(+) αβ-IELs preferentially accumulate in pIgR(-/-) mice through the enhanced differentiation of immature haematopoietic precursor cells, which may subsequently result in the disruption of epithelial integrity.

A characteristic mucosal immune response involves the production of antigen-specific secretory immunoglobulin A (SIgA) antibodies. In order to study transcytosis by mimicking the SIgA secretion and to screen for SIgA secretion-promoting substances, we developed a model system of a transfected Madin-Darby canine kidney (MDCK) cell line that expresses the human polymeric immunoglobulin receptor (pIgR). We thus isolated the human dIgA (dimeric IgA)/pIgA (polymeric IgA) complex as the binding ligands. In the present study, a recombinant vector encoding the human pIgR gene was constructed and infected into MDCK cells. Following reverse transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunofluorescence staining, we confirmed that pIgR was expressed in the transfectant MDCK-pIgR cells and was located at the basolateral side of the cell surface. We also confirmed the coexistence of the dIgA/pIgA complex in the IgA myeloma serum. The covalent dIgA/pIgA complex was then isolated from the serum of an IgA multiple myeloma patient using an ÄKTA purifier operation system with a HiPrep 16/60 Sephacryl S-300 HR column, in order to utilize the complex as transcytosis ligands for human pIgR. Finally, we confirmed the uptake of the isolated human dIgA/pIgA complex into MDCK-pIgR cells. We demonstrated that the human dIgA/pIgA complex was transcytosed into the apical side of the monolayer cells. Therefore, our MDCK-human pIgR cell transcytosis model is an operational system and can be used for screening functional food components that promote dIgA/pIgR transcytosis as well as SIgA secretion.

Although Apostichopus japonicus is recognized as a food and drug resource with significant immunomodulatory activity, its role in regulating the mucosal immunity remains unclear. This study aimed to explore the effects of dietary A. japonicus on mucosal immunity with an immunosuppressive mouse model. The expression of lysozyme, secretory immunoglobulin A(sIgA), and immunoglobulin A(IgA) as well as polymeric immunoglobulin receptor(pIgR) in respiratory and intestine organs was investigated. The results showed that A. japonicus could improve both the systematic and mucosal immunity. The expression of lysozyme, sIgA, and IgA in the respiratory organ was increased more significantly. Consumption of A. japonicus with the dose of 512 mg kg−1, which equals to 1/2 sea cucumber per day for adults, showed better effects. This study elucidated positive effects of A. japonicus on mucosal immunity for the first time, suggesting that moderate consumption of A. japonicus is helpful in improving mucosal immunity and preventing exogenous infection.

Secretory IgA (SIgA) antibodies in the intestinal tract form the first line of antigen-specific immune defense, preventing access of pathogens as well as commensal microbes to the body proper. SIgA is transported into external secretions by the polymeric immunoglobulin receptor (pIgR). Evidence is reported here that the gut microbiota regulates production of SIgA and pIgR, which act together to regulate the composition and activity of the microbiota. SIgA in the intestinal mucus layer helps to maintain spatial segregation between the microbiota and the epithelial surface without compromising the metabolic activity of the microbes. Products shed by members of the microbial community promote production of SIgA and pIgR by activating pattern recognition receptors on host epithelial and immune cells. Maternal SIgA in breast milk provides protection to newborn mammals until the developing intestinal immune system begins to produce its own SIgA. Disruption of the SIgA-pIgR-microbial triad can increase the risk of infectious, allergic and inflammatory diseases of the intestine.

Colonization of Streptococcus pneumoniae (pneumococci) is a prerequisite for bacterial dissemination and their capability to enter the bloodstream. Pneumococci have evolved various successful strategies to colonize the mucosal epithelial barrier of humans. A pivotal mechanism of host cell invasion implicated with invasive diseases is promoted by the interaction of pneumococcal PspC with the polymeric Ig-receptor (pIgR). However, the mechanism(s) of pneumococcal endocytosis and the intracellular route of pneumococci upon uptake by the PspC-pIgR-interaction are not known. Here, we demonstrate by using a combination of pharmacological inhibitors and genetics interference approaches the involvement of active dynamin-dependent caveolae and clathrin-coated vesicles for pneumococcal uptake via the PspC-pIgR mechanism. Depleting cholesterol from host cell membranes and disruption of lipid microdomains impaired pneumococcal internalization. Moreover, chemical inhibition of clathrin or functional inactivation of dynamin, caveolae or clathrin by RNA interference significantly affected pneumococcal internalization suggesting that clathrin-mediated endocytosis (CME) and caveolae are involved in the bacterial uptake process. Confocal fluorescence microscopy of pIgR-expressing epithelial cells infected with pneumococci or heterologous Lactococcus lactis expressing PspC demonstrated bacterial co-localization with fluorescent-tagged clathrin and early as well as recycling or late endosomal markers such as Lamp1, Rab5, Rab4, and Rab7, respectively. In conclusion these data suggest that PspC-promoted uptake is mediated by both CME and caveolae. After endocytosis pneumococci are routed via the endocytic pathway into early endosomes and are then sorted into recycling or late endosomes, which can result in pneumococcal killing in phagolysosomes or transcytosis via recycling endosomes.

IgG antibodies are abundantly present in the vasculature but to a much lesser extent in mucosal tissues. This contrasts with antibodies of the IgA and IgM isotype that are present at high concentration in mucosal secretions due to active delivery by the polymeric Ig receptor (pIgR). IgG is the preferred isotype for therapeutic mAb development due to its long serum half-life and robust Fc-mediated effector function, and it is utilized to treat a diverse array of diseases with antigen targets located in the vasculature, serosa, and mucosa. As therapeutic IgG antibodies targeting the luminal side of mucosal tissue lack an active transport delivery mechanism, we sought to generate IgG antibodies that could be transported via pIgR, similarly to dimeric IgA and pentameric IgM. We show that an anti-Pseudomonas aeruginosa IgG fused with pIgR-binding peptides gained the ability to transcytose and be secreted via pIgR. Consistent with these results, pIgR-binding IgG antibodies exhibit enhanced localization to the bronchoalveolar space when compared with the parental IgG antibody. Furthermore, pIgR-binding mAbs maintained Fc-mediated functional activity and promoted enhanced survival compared with the parental mAb in a P. aeruginosa acute pneumonia model. Our results suggest that increasing IgG accumulation at mucosal surfaces by pIgR-mediated active transport can improve the efficacy of therapeutic mAbs that act at these sites.

The polymeric immunoglobulin receptor (pIgR) is an essential component of the mucosal immune system in jawed vertebrates including teleost fish, which mediate transepithelial transport of secretory immunoglobulins (sIgs) to protect organisms against environmental pathogens. In this study, we firstly cloned and identified the pIgR from dojo loach (Misgurnus anguillicaudatus). The full-length cDNA of Ma-pIgR was of 1145 bp, containing an open reading frame (ORF) of 1101 bp encoded a predicted protein of 336 amino acids. The structure of Ma-pIgR is comprised of a signal peptide, a transmembrane region, an intracellular region and an extracellular region with two Ig-like domains (ILDs), which are similar to their counterparts described in other teleosts. Multiple sequence alignment and phylogenetic analysis showed the dojo loach is closely related to the fish family Cyprinidae. The transcriptional level of Ma-pIgR was detected by quantitative real-time PCR (qRT-PCR) in different tissues and high expression was found in liver, skin, kidney, eye, fin and gills. Two infection models of the loach with bacteria (Aeromonas hydrophila) and parasite (Ichthyophthirius multifiliis) were constructed for the first time. Histological studies showed the goblet cells in skin significantly increased and the ratio of gill length to width also significantly changed after challenged with A.hydrophila. Both challenge experiments resulted in the significant up-regulated expression of Ma-pIgR not only in kidney and spleen, but also in skin and gills. Our results suggest that pIgR may play an important role in skin and gill mucosal immunity to protect the loach against bacteria and parasite.

Three different receptors that interact with the constant domains of IgM have been identified: the polymeric immunoglobulin (Ig) receptor (PIGR), the dual receptor for IgA/IgM (FcαµR) and the IgM receptor (FcµR). All of them are related in structure and located in the same chromosomal region in mammals. The functions of the PIGRs are to transport IgM and IgA into the intestinal lumen and to saliva and tears, whereas the FcαµRs enhance uptake of immune complexes and antibody coated bacteria and viruses by B220+ B cells and phagocytes, as well as dampening the Ig response to thymus-independent antigens. The FcµRs have broad-spectrum effects on B-cell development including effects on IgM homeostasis, B-cell survival, humoral immune responses and also in autoantibody formation. The PIGR is the first of these receptors to appear during vertebrate evolution and is found in bony fish and all tetrapods but not in cartilaginous fish. The FcµR is present in all extant mammalian lineages and also in the Chinese and American alligators, suggesting its appearance with early reptiles. Currently the FcαµR has only been found in mammals and is most likely the evolutionary youngest of the three receptors. In bony fish, the PIGR has either 2, 3, 4, 5 or 6 extracellular Ig-like domains, whereas in amphibians, reptiles and birds it has 4 domains, and 5 in all mammals. The increase in domain number from 4 to 5 in mammals has been proposed to enhance the interaction with IgA. Both the FcαµRs and the FcµRs contain only one Ig domain; the domain that confers Ig binding. In both of these receptors this domain shows the highest degree of sequence similarity to domain 1 of the PIGR. All Ig domains of these three receptors are V type domains, indicating they all have the same origin although they have diversified extensively in function during vertebrate evolution by changing expression patterns and cytoplasmic signaling motifs.

Airway epithelial cells (AECs) display remarkable plasticity in response to infectious stimuli and their functional adaptations are critical for antimicrobial immunity. However, the roles of AECs and humoral mediators to host defense in non-communicable lung inflammation remain elusive. We dissected pulmonary defense against Streptococcus pneumoniae in hosts with pre-existing inflammatory conditions (SPC-HAxTCR-HA mice). Lung tissue transcriptomics and bronchoalveolar lavage fluid (BALF) proteomics revealed an induction of humoral defense mechanisms in inflamed lungs. Accordingly, besides antibacterial proteins and complement components being overrepresented in inflamed lungs, elevated polymeric immunoglobulin receptor (pIgR)-expression in AECs correlated with increased secretory immunoglobulin (SIg) transport. Consequently, opsonization assays revealed augmented pneumococcal coverage by SIgs present in the BALF of SPC-HAxTCR-HA mice, which was associated with enhanced antipneumococcal resistance. These findings emphasize the immunologic potential of AECs as well as their central role in providing antibacterial protection and put forward pIgR as potential target for therapeutic manipulation in infection-prone individuals.

Background: The mechanism underlying transient increases in immunoglobulin (Ig) A concentrations in the cecal contents of rats fed fructo-oligosaccharide (FOS) is unclear.Objective: This study was designed to test whether increased IgA concentrations represent one aspect of the inflammatory response to increased permeability induced by FOS in the cecum.Methods: Seven-week-old male Wistar rats were fed a fiber-free semipurified diet (FFP) with or without supplemental FOS (60 g/kg diet) for 9 or 58 d [experiment (expt.) 1], 7 d (expt. 2), or 7 or 56 d (expt. 3). In addition to measuring IgA concentrations in cecal content, we assessed gut permeability, inflammatory responses (expt. 1), the number of IgA plasma cells in the cecal lamina propria, polymeric Ig receptor (pIgR) expression in the cecal mucosa (expt. 2), and the condition of the cecal mucus layer (expt. 3).Results: The cecal IgA concentration in the FOS-fed rats was 15-fold higher than that of the rats fed FFP for 9 d (P < 0.05). Gut permeability estimated by urinary chromium-EDTA excretion, bacterial translocation to mesenteric lymph nodes, myeloperoxidase activity, and expression of inflammatory cytokine genes in the cecal mucosa was greater in the FOS-fed rats than in the rats fed FFP for 9 d. These effects were not observed in the rats fed FOS for 58 d (expt. 1). Accompanying the higher cecal IgA concentration, pIgR protein and the number of IgA plasma cells in the cecal mucosa were higher in the FOS-fed rats than in the rats fed FFP for 7 d (expt. 2). Destruction of the mucus layer on the epithelial surface, as evidenced by Alcian blue staining in the cecal sections, was evident in the rats fed FOS for 7 d, but the mucus layer appeared normal in the rats fed FOS for 56 d (expt. 3).Conclusions: These findings suggest that transient increases in cecal IgA concentrations induced by FOS in rats are associated with mucosal inflammation in response to increased gut permeability; these are presumably evoked by disruption of the cecal mucus barrier. The observed responses could contribute to the maturation of the gut immune system.

The effect of ethanol (EtOH) on the gut immune system was analyzed using an experimental model previously described, where EtOH was provided ad libitum in the drinking water in a 20% w/v concentration for up to 12weeks. Dendritic cells, T cells and macrophages were analyzed in Peyer's patches and the small intestines using flow cytometry. Cytokine and immunoglobulin levels were analyzed in sera, feces, and homogenates from small and large intestines and lungs. Decreases in the proportion of T cells and alterations in dendritic cells and macrophages were observed after EtOH treatment. Levels of immunoglobulin A (IgA) increased in tissue homogenates but decreased in small intestine fecal contents. Meanwhile poly-immunoglobulin receptor (pIgR) levels decreased in tissue homogenates and fecal contents. Levels of cytokines associated with the regulation of pIgR expression decreased for IL-10 and TGF-β, and increased for IFN-γ and IL-17 in the small intestine. The data indicate that chronic EtOH consumption disrupts the homeostasis of the mucosal immune system by altering the phenotype and functionality of multiple immune cell types, leading to a diminished secretion of SIgA, due to pIgR expression decreased.

Ancestral protein reconstruction allows the resurrection and characterization of ancient proteins based on computational analyses of sequences of modern-day proteins. Unfortunately, many protein families are highly divergent and not suitable for sequence-based reconstruction approaches. This limitation is exemplified by the antigen receptors of jawed vertebrates (B- and T-cell receptors), heterodimers formed by pairs of Ig domains. These receptors are believed to have evolved from an extinct homodimeric ancestor through a process of gene duplication and diversification; however molecular evidence has so far remained elusive. Here, we use a structural approach and laboratory evolution to reconstruct such molecules and characterize their interaction with antigen. High-resolution crystal structures of reconstructed homodimeric receptors in complex with hen-egg white lysozyme demonstrate how nanomolar affinity binding of asymmetrical antigen is enabled through selective recruitment and structural plasticity within the receptor-binding site. Our results provide structural evidence in support of long-held theories concerning the evolution of antigen receptors, and provide a blueprint for the experimental reconstruction of protein ancestry in the absence of phylogenetic evidence.

Polymeric immunoglobulin receptors (pIgR) are key participants in the formation and secretion of secretory IgA (S-IgA), which is critical for the prevention of microbial infection and colonization in the respiratory system. Although increased respiratory colonization and infections are common in HIV/AIDS, little is known about the expression of pIgR in the airway mucosa of these patients. To address this, the expression levels of pIgR in the tracheal mucosa and lungs of SHIV/SIV-infected rhesus macaques were examined by real-time RTPCR and confocal microscopy. We found that the levels of both PIGR mRNA and pIgR immunoreactivity were lower in the tracheal mucosa of SHIV/SIV-infected rhesus macaques than that in non-infected rhesus macaques, and the difference in pIgR immunoreactivity was statistically significant. IL-17A, which enhances pIgR expression, was also changed in the same direction as that of pIgR. In contrast to changes in the tracheal mucosa, pIgR and IL-17A levels were higher in the lungs of infected rhesus macaques. These results indicated abnormal pIgR expression in SHIV/SIV, and by extension HIV infections, which might partially result from IL-17A alterations and might contribute to the increased microbial colonization and infection related to pulmonary complications in HIV/AIDS.

Netrin-1 was the first axon guidance molecule to be discovered in vertebrates and has a strong chemotropic function for axonal guidance, cell migration, morphogenesis and angiogenesis. It is a secreted axon guidance cue that can trigger attraction by binding to its canonical receptors Deleted in Colorectal Cancer (DCC) and Neogenin or repulsion through binding the DCC/Uncoordinated (Unc5) A-D receptor complex. The crystal structures of Netrin-1/receptor complexes have recently been revealed. These studies have provided a structure based explanation of Netrin-1 bi-functionality. Netrin-1 and its receptor are continuously expressed in the adult nervous system and are differentially regulated after nerve injury. In the adult spinal cord and optic nerve, Netrin-1 has been considered as an inhibitor that contributes to axon regeneration failure after injury. In the peripheral nervous system, Netrin-1 receptors are expressed in Schwann cells, the cell bodies of sensory neurons and the axons of both motor and sensory neurons. Netrin-1 is expressed in Schwann cells and its expression is up-regulated after peripheral nerve transection injury. Recent studies indicated that Netrin-1 plays a positive role in promoting peripheral nerve regeneration, Schwann cell proliferation and migration. Targeting of the Netrin-1 signaling pathway could develop novel therapeutic strategies to promote peripheral nerve regeneration and functional recovery.

Breastfeeding is important for mammals, providing immunological and microbiological advantages to neonates, together with the nutritional supply from the mother. However, the mechanisms of this functional diversity in the mammary gland remain poorly characterized. Here, we show that, similar to the gastrointestinal tract, the mammary gland develops immune and microbial environments consisting of immunoglobulin A (IgA) and the microflora, respectively, both of which are important for protecting neonates and the mother from infectious diseases. The IgA production and microflora development are coordinated in the gastrointestinal tract but seem to be independently regulated in the mammary gland. In particular, the chemokine (C-C motif) ligand 28 and poly-Ig receptor, crucial molecules for the IgA production in milk, were expressed normally in germ-free lactating mice but were almost undetectable in postweaning mothers, regardless of the microflora presence. Our findings offer insights into potentially improving the quality of breastfeeding, using both immunological and microbiological approaches.

The protozoan parasite Giardia is a highly prevalent intestinal pathogen with a wide host range. Data obtained in mice, cattle and humans revealed the importance of IL-17A in the development of a protective immune response against Giardia. The aim of this study was to further unravel the protective effector mechanisms triggered by IL-17A following G. muris infection in mice, by an RNA-sequencing approach. C57BL/6 WT and C57BL/6 IL-17RA KO mice were orally infected with G. muris cysts. Three weeks post infection, intestinal tissue samples were collected for RNA-sequencing, with samples from uninfected C57BL/6 WT and C57BL/6 IL-17RA KO animals serving as negative controls. Differential expression analysis showed that G. muris infection evoked the transcriptional upregulation of a wide array of genes, mainly in animals with competent IL-17RA signaling. IL-17RA signaling induced the production of various antimicrobial peptides, such as angiogenin 4 and α- and β-defensins and regulated complement activation through mannose-binding lectin 2. The expression of the receptor that regulates the secretion of IgA into the intestinal lumen, the polymeric immunoglobulin receptor, was also dependent on IL-17RA signaling. Interestingly, the transcriptome data showed for the first time the involvement of the circadian clock in the host response following Giardia infection.

Joining chain (J chain) is a small polypeptide that regulates multimerization of secretory IgM and IgA, the only two mammalian Igs capable of forming multimers. J chain also is required for poly-Ig receptor–mediated transport of these Ig classes across the mucosal epithelium. It is generally assumed that all plasma cells express J chain regardless of expressed isotype, despite the documented presence of J chain− plasma cells in mammals, specifically in all monomeric IgA-secreting cells and some IgG-secreting cells. Compared with most other immune molecules, J chain has not been studied extensively, in part because of technical limitations. Even the reported phenotype of the J chain–knockout mouse is often misunderstood or underappreciated. In this short review, we discuss J chain in light of the various proposed models of its expression and regulation, with an added focus on its evolutionary significance, as well as its expression in different B cell lineages/differentiation states.