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Epidemiological evidence establishes obesity as an independent risk factor for increased susceptibility and severity to viral respiratory pneumonias associated with H1N1 influenza and SARS-CoV-2 pandemics. Given the global obesity prevalence, a better understanding of the mechanisms behind obese susceptibility to infection is imperative. Altered immune cell metabolism and function are often perceived as a key causative factor of dysregulated inflammation. However, the contribution of adipocytes, the dominantly altered cell type in obesity with broad inflammatory properties, to infectious disease pathogenesis remains largely ignored. Thus, skewing of adipocyte-intrinsic cellular metabolism may lead to the development of pathogenic inflammatory adipocytes, which shape the overall immune responses by contributing to either premature immunosenescence, delayed hyperinflammation, or cytokine storm in infections. In this review, we discuss the underappreciated contribution of adipocyte cellular metabolism and adipocyte-produced mediators on immune system modulation and how such interplay may modify disease susceptibility and pathogenesis of influenza and SARS-CoV-2 infections in obese individuals.

Background Leptin is an adipose tissue-derived cytokine that plays a role in energy regulation and immune functions. High leptin levels and obesity have been associated with decreased risk of developing active TB. We aimed to characterize the association between body mass index (BMI) and leptin levels in patients at different stages of tuberculosis (TB). Methods Data from a cross-sectional cardiovascular risk study of 40 to 70 years old individuals enrolled in Lima, Peru, and Cincinnati, US, were analyzed. Four categories based on TB and treatment status were defined: no TB infection (QuantiFERON-TB test negative; n= 31), latent TB infection (LTBI; QuantiFERON-TB test positive; n= 43), active TB on treatment (in the continuation TB treatment phase; n= 30), and post-TB (within one year of TB treatment completion; n=16). BMI and plasma leptin levels were compared among the four groups using the Kruskal-Wallis test, followed by Dunn’s multiple comparison test if differences were found in the Kruskal-Wallis test. Multivariate ordered logistic regression models were used to assess factors associated with leptin levels, adjusted for potential confounders. Results The median age was 53 years, and 51% were female. BMI was different between study groups (p< 0.01), with LTBI individuals having the highest BMI compared to other groups; see Figure 1A. Leptin levels were marginally low in the group with active TB on treatment, but no significant differences were found between groups (p=0.44; see Figure 1B). In multivariate analysis, leptin was associated with female sex (OR 23, 95%CI, 9-58), BMI (OR, 1.5, 95%CI, 1.2-1.7), and coronary plaque ≥25% stenosis (OR, 0.29, 95%CI, 0.08-0.99). Body mass index (BMI) and plasma leptin levels in participants with negative QuantiFERON-TB test (QFN-), latent tuberculosis infection (LTBI), active tuberculosis on treatment (ATBT), and post-TB treatment (TB-treated). Significance was determined using the Kruskal-Wallis test, followed by Dunn’s multiple comparison test if the Kruskal- Wallis test p-value was Conclusion LTBI individuals had a higher BMI compared to persons with active TB on treatment and post-TB. Higher leptin levels were associated with higher BMI, but we found no association between leptin and TB status in our cohort. Disclosures All Authors: No reported disclosures

Severe Clostridiodes difficile infection (CDI) is life-threatening and responds poorly to treatment. Obesity is associated with development of severe CDI. Therefore, to define the mechanisms that exacerbate disease severity, we examined CDI pathogenesis in high-fat diet (HFD)-fed obese mice. Compared to control mice, HFD-fed mice failed to clear C. difficile bacteria which resulted in protracted diarrhea, weight loss and colonic damage. After infection, HFD-induced obese mice had an intestinal bile acid (BA) pool that was dominated by primary BAs which are known promoters of C. difficile spore germination, and lacked secondary BAs that inhibit C. difficile growth. Concurrently, synthesis of primary BAs from liver was significantly increased in C. difficile-infected HFD-fed mice. A key pathway that regulates hepatic BA synthesis is via feedback inhibition from intestinal Farnesoid X receptors (FXRs). Our data reveal that the proportion of FXR agonist BAs to FXR antagonist BAs in the intestinal lumen was significantly reduced in HFD-fed mice after CDI. Treatment of HFD-fed mice with an FXR agonist Obeticholic acid, resulted in decreased primary BA synthesis, fewer C. difficile bacteria and better CDI outcomes. Thus, OCA treatment holds promise as a therapy for severe CDI.

Clostridium difficile is an important cause of nosocomial diarrhea in the western world. Toxins (A, B, and binary toxins) generated by C. difficile bacteria damage intestinal epithelial cells. Hallmarks of host response to C. difficile infection (CDI) include upregulation of inflammatory mediators and tissue infiltration by immune cells. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that is known to enhance the host immune response to infectious pathogens. Additionally, MIF can adversely impact host survival to numerous infections. The role of MIF in the pathogenesis of CDI remains poorly understood. Here, we show that patients with CDI had significantly higher circulating MIF compared to patients who had diarrhea but tested negative for C. difficile (non-CDI controls). Similarly, in a mouse model, C. difficile challenge significantly increased levels of plasma and tissue MIF. Antibody-mediated depletion of MIF decreased C. difficile-induced inflammatory responses, clinical disease, and mortality. Together, these results uncover a potential role for MIF in exacerbating CDI and suggest that use of anti-MIF antibodies may represent a therapeutic strategy to curb host inflammatory responses and improve disease outcomes in CDI.

Clostridium difficile is the leading cause of nosocomial infections in the United States. Clinical disease outcomes after C. difficile infection (CDI) are dependent on intensity of host inflammatory responses. Specifically, peak peripheral white blood cell (WBC) count >20 × 109 l−1 is an indicator of adverse outcomes in CDI patients, and is associated with higher 30-day mortality. We show that homozygosity for a common single nucleotide polymorphism (Q to R mutation in leptin receptor that is present in up to 50% of people), significantly increases the risk of having peak peripheral WBC count >20 × 109 l−1 (odds ratio=5.41; P=0.0023) in CDI patients. In a murine model of CDI, we demonstrate that mice homozygous for the same single nucleotide polymorphism (RR mice) have more blood and tissue leukocytes (specifically neutrophils), exaggerated tissue inflammation, and higher mortality as compared with control mice, despite similar pathogen burden. Further, we show that neutrophilia in RR mice is mediated by gut microbiota-directed expression of CXC chemokine receptor 2 (CXCR2), which promotes the release of neutrophils from bone marrow reservoir. Overall these studies provide novel mechanistic insights into the role of human genetic polymorphisms and gut microbiota in regulating the fundamental biological process of CDI-induced neutrophilia.

Background Kidney transplantation (KTxp) provides dialysis independence, improved quality of life, and prolonged life expectancy for patients with end-stage renal disease. Before and during the early antiretroviral therapy era, KTxp was not a consideration for patients with end-stage renal disease who were HIV-positive (HIV+ve) given their short life expectancy and prevailing organ procurement constraints. Recent advancements in antiretroviral therapy and HIV care have overhauled this paradigm and KTxp has now been performed for several years, however, pragmatic studies documenting outcomes are lacking. We herein document the effectiveness of KTxp in patients who are HIV+ve by reporting clinical and health care utilization outcomes in the United States. Methods Utilizing the Inpatient Databases of the Healthcare Cost & Utilization Project spanning 2008-2013, we identified all adult recipients of KTxp by procedural codes and recipients who are HIV+ve by ICD-9 codes. We extracted demographic, clinical, and resource utilization variables and compared recipients who are HIV+ve with those who are HIV-negative (HIV-ve). We then performed descriptive statistics and multivariate analysis using logistic regression to assess the effect of HIV on clinical and utilization outcomes. Results A total of 104,137 patients had kidney transplants during the study period. Of the total, 605 patients were HIV+ve. Infections rates were similar among patients who were HIV+ve and HIV-ve (odds ratio [OR] 1.18, confidence interval [CI] 0.58–2.40; P = .652). In-hospital mortality rates were also similar (OR 0.83, CI 0.18–3.69; P = .80). Hospital charges for patients who were HIV+ve were no different from patients who were HIV-ve ($195,099 ± 1074 vs $186,567 ± 9558; P = .38). Conclusion Clinical and fiscal outcomes are comparable among patients who are HIV+ve and HIV-ve during transplant hospitalization.

Obesity is among the most pressing health concerns in the world since it is increasingly common even in the developing world, and is clearly associated with increased risk for chronic debilitating diseases and death. Furthermore, obesity can influence the pathogenesis of infectious diseases by affecting the balance of pathogen clearance and pathological inflammation. The mechanisms that result in enhanced inflammation in obese individuals are poorly understood. Clostridium difficile is a major cause of nosocomial infections worldwide. Recent studies have shown that obesity is associated with increased risk of C. difficile infections. In this review, we will discuss our current knowledge of the role of obesity in determining risk of C. difficile infections, and focus on the role of the adipose tissue-derived cytokine leptin in C. difficile infections.

The role of leptin in the mucosal immune response to Clostridium difficile colitis, a leading cause of nosocomial infection, was studied in humans and in a murine model. Previously, a mutation in the receptor for leptin ( LEPR ) was shown to be associated with susceptibility to infectious colitis and liver abscess due to Entamoeba histolytica as well as to bacterial peritonitis. Here we discovered that European Americans homozygous for the same LEPR Q223R mutation (rs1137101), known to result in decreased STAT3 signaling, were at increased risk of C. difficile infection (odds ratio, 3.03; P = 0.015). The mechanism of increased susceptibility was studied in a murine model. Mice lacking a functional leptin receptor ( db/db ) had decreased clearance of C. difficile from the gut lumen and diminished inflammation. Mutation of tyrosine 1138 in the intracellular domain of LepRb that mediates signaling through the STAT3/SOCS3 pathway also resulted in decreased mucosal chemokine and cell recruitment. Collectively, these data support a protective mucosal immune function for leptin in C. difficile colitis partially mediated by a leptin-STAT3 inflammatory pathway that is defective in the LEPR Q223R mutation. Identification of the role of leptin in protection from C. difficile offers the potential for host-directed therapy and demonstrates a connection between metabolism and immunity.

Clostridium difficile is currently the leading cause of nosocomial infections in the United States, with an estimated cost of $4.8 billion to the healthcare industry annually [1]. The incidence of infection continues to rise in healthcare and community-settings, in part because of the emergence of a new hypervirulent strain, BI/NAP1 [2]. Despite therapy, strains with increased virulence have resulted in death within 30 day in up to 15% of patients [3] and disease recurrence in 20%–40% of cases [2]. The aim of this study was to evaluate the host inflammatory response to C. difficile infection. It has been hypothesized that the intensity of the host response and resulting inflammation may be correlated with disease severity. Understanding and targeting host-based mediators of inflammation may provide a target for more effective therapy. Interleukin-23 (IL-23) causes inflammation because of its ability to induce proinflammatory cytokine production by innate and immune cells, such as interleukin 17A (IL-17A), interleukin 17F (IL-17F), and interleukin 21 (IL-21), and its ability to neglect the induction and maintenance of the antiinflammatory cytokine interleukin 10 (IL-10) [4–7]. Previous studies have implicated IL-23 signaling as a precursor to colitis in models of inflammatory bowel disease (IBD) [8, 9]. This prompted us to examine its role in the development of C. difficile­­–associated pathology. Colon biopsy specimens from patients with C. difficile colitis demonstrated the presence of IL-23–producing infiltrating white blood cells in the lamina propria. We used the murine model of C. difficile colitis to test the role of IL-23 signaling during infection. Mice lacking IL-23 signaling had decreased disease severity, as manifest by clinical scoring and survival proportions. The implications of these studies for understanding the pathogenesis of C. difficile disease and potential host-targeted therapy are discussed.

Clostridium difficile is the leading cause of healthcare-associated infections in the United States. Clinically, C. difficile-associated disease can present as asymptomatic colonization, self-limited diarrheal illness or severe colitis (that may result in death). This variability in disease course and outcomes suggests that host factors play an important role as key determinants of disease severity. Currently, there are several scoring indices to estimate severity of C. difficile-associated disease. Leukocytosis and renal failure are considered to be the most important predictors of C. difficile disease severity in hosts with a normal immune system. The degree of leukocytosis which is considered significant for severe disease and how it is scored vary amongst scoring indices. None of the scores have been prospectively validated, and while total WBC count is useful to estimate the magnitude of the host response in most patient populations, in immune-compromised patients like those receiving chemotherapy, solid organ transplant patients or hematopoietic stem cell transplants the WBC response can be variable or even absent making this marker of severity difficult to interpret. Other cellular subsets like neutrophils, eosinophils and lymphocytes provide important information about the host immune status and play an important role in the immune response against C. difficile infection. However, under the current scoring systems the role of these cellular subsets have been underestimated and only total white blood cell counts are taken into account. In this review we highlight the role of host leukocyte response to C. difficile challenge in the normal and immunocompromised host, and propose possible ways that would allow for a better representation of the different immune cell subsets (neutrophils, lymphocytes and eosinophils) in the current scoring indices.

Clostridium difficile is the most important cause of nosocomial infectious diarrhea in the western world. C. difficile infections are a major healthcare burden with approximately 500,000 new cases every year and an estimated annual cost of nearly $1 billion in the U.S. Furthermore, the infections are no longer restricted to health care facilities, and recent studies indicate spread of C. difficile infection to the community as well. The clinical spectrum of C. difficile infection ranges from asymptomatic colonization to severe diarrhea, fulminant colitis and death. This spectrum results from a complex interplay between bacterial virulence factors, the colonic microbiome and the host inflammatory response. The overall vigor of host inflammatory response is believed to be an important determinant of C. difficile disease severity, and a more robust immune response is associated with worse outcomes. Neutrophils are the primary cells that respond to C. difficile invasion and neutrophilic inflammation is the hallmark of C. difficile-associated disease. In this review, we will focus on the role of neutrophils (infiltration to infected tissue, pathogen clearance and resolution of inflammation) in the immuno-pathogenesis of C. difficile-associated disease (CDAD).

Clostridium difficile is the causal agent of antibiotic-associated diarrhea and is a leading cause of hospital-acquired infections in the US. C. difficile has been known to cause severe diarrhea and colitis for more than 30 years, but the emergence of a newer, hypervirulent strain of C. difficile (BI/NAP1) has further compounded the problem, and recently both the number of cases and mortality associated with C. difficile-associated diarrhea have been increasing. One of the major drivers of disease pathogenesis is believed to be an excessive host inflammatory response. A better understanding of the host inflammation and immune mechanisms that modulate the course of disease and control host susceptibility to C. difficile could lead to novel (host-targeted) strategies for combating the challenges posed by this deadly infection. This review summarizes our current knowledge of the host inflammatory response during C. difficile infection.

SummarySurviving infection represents a balance between the proinflammatory responses needed to eliminate the pathogen, and anti-inflammatory signals limiting damage to the host. IL-10 is a potent immunosuppressive cytokine whose impact is determined by the timing and localization of release. We show that NK cells rapidly express IL-10 during acute infection with diverse rapidly disseminating pathogens. The proinflammatory cytokine IL-12 was necessary and sufficient for NK cell induction of IL-10. NK cells from mice with systemic parasitic infection inhibited dendritic cell release of IL-12 in an IL-10-dependent manner, and NK cell depletion resulted in elevated serum IL-12. These data suggest an innate, negative feedback loop in which IL-12 limits its own production by eliciting IL-10 from NK cells. In contrast to disseminating pathogens, locally restricted infections did not elicit NK cell IL-10. Thus systemic infections uniquely engage NK cells in an IL-10-mediated immunoregulatory circuit that functions to alleviate inflammation.

Regulatory T cells (T(reg) cells) that express the transcription factor Foxp3 suppress the activity of other cells. Here we show that interleukin 10 (IL-10) produced by CD11b(+) myeloid cells in recombination-activating gene 1-deficient (Rag1(-/-)) recipient mice was needed to prevent the colitis induced by transferred CD4(+)CD45RB(hi) T cells. In Il10(-/-)Rag1(-/-) mice, T(reg) cells failed to maintain Foxp3 expression and regulatory activity. The loss of Foxp3 expression occurred only in recipients with colitis, which indicates that the requirement for IL-10 is manifested in the presence of inflammation. IL-10 receptor-deficient (Il10rb(-/-)) T(reg) cells also failed to maintain Foxp3 expression, which suggested that host IL-10 acted directly on the T(reg) cells. Our data indicate that IL-10 released from myeloid cells acts in a paracrine manner on T(reg) cells to maintain Foxp3 expression.

IL-10 plays a central role in restraining the vigor of inflammatory responses, but the critical cellular sources of this counter-regulatory cytokine remain speculative in many disease models. Using a novel IL-10 transcriptional reporter mouse, we found an unexpected predominance of B cells (including plasma cells) among IL-10-expressing cells in peripheral lymphoid tissues at baseline and during diverse models of in vivo immunological challenge. Use of a novel B cell-specific IL-10 knockout mouse revealed that B cell-derived IL-10 nonredundantly decreases virus-specific CD8+ T cell responses and plasma cell expansion during murine cytomegalovirus infection and modestly restrains immune activation after challenge with foreign Abs to IgD. In contrast, no role for B cell-derived IL-10 was evident during endotoxemia; however, although B cells dominated lymphoid tissue IL-10 production in this model, myeloid cells were dominant in blood and liver. These data suggest that B cells are an underappreciated source of counter-regulatory IL-10 production in lymphoid tissues, provide a clear rationale for testing the biological role of B cell-derived IL-10 in infectious and inflammatory disease, and underscore the utility of cell type-specific knockouts for mechanistic limning of immune counter-regulation.

Aeroallergy results frommaladaptiveimmuneresponses toubiquitous, otherwise innocuous environmental proteins 1 . Although the proteinstargetedbyaeroallergicresponses representa tinyfraction of the airborne proteins humans are exposed to, allergenicity is a quite public phenomenon—the same proteins typically behave as aeroallergens across the human population. Why particular proteins tend to act as allergens in susceptible hosts is a fundamental mechanistic question that remains largely unanswered. The main house-dust-mite allergen, Derp2, has structural homology with MD-2 (also known as LY96), the lipopolysaccharide (LPS)-binding component of the Toll-like receptor (TLR) 4 signalling complex 2–4 . HereweshowthatDerp2alsohasfunctionalhomology,facilitating signalling through direct interactions with the TLR4 complex, and reconstituting LPS-driven TLR4 signalling in the absence of MD-2. Mirroring this, airway sensitization and challenge with Derp2 led to experimental allergic asthma in wild type and MD-2-deficient, butnotTLR4-deficient,mice.OurresultsindicatethatDerp2tends to be targeted by adaptive immune responses because of its autoadjuvant properties. The fact that other members of the MD-2-like lipid-binding family are allergens, and that most defined major allergens are thought to be lipid-binding proteins 5 ,s uggests that intrinsicadjuvantactivitybysuchproteinsandtheiraccompanying lipid cargo may have some generality as a mechanism underlying the phenomenon of allergenicity. Although the potential biological significance of several allergens having protease activity has received experimental attention 5,6 , cogent mechanistic hypotheses for why most aeroallergens have a propensitytogeneratemaladaptiveeffectorT-cellresponsesarelacking. TLRs, receptors for conserved microbial structures, have a critical role in the controlling initiation and class specification of adaptive immune responses by antigen-presenting cells (APCs) 7 . Exogenous antigen presentation by APCs in the absence of direct TLR stimulation generally leads to tolerance 8 . Moreover, efficient generation of effector T-cell responses by APCs is dependent on thepresence ofTLRligandsinthephagosomecontaining theantigen being presented 9 . House dust mites are a major source of aeroallergens for patients with allergic asthma 10 . Concentrated in mite faecal pellets 11 , the

Crossing the Cyp1a1/1a2(-/-) double-knockout mouse with the Cyp1b1(-/-) single-knockout mouse, we generated the Cyp1a1/1a2/1b1(-/-) triple-knockout mouse. In this triple-knockout mouse, statistically significant phenotypes (with incomplete penetrance) included slower weight gain and greater risk of embryolethality before gestational day 11, hydrocephalus, hermaphroditism, and cystic ovaries. Oral benzo[a]pyrene (BaP) daily for 18 days in the Cyp1a1/1a2(-/-) produced the same degree of marked immunosuppression as seen in the Cyp1a1(-/-) mouse; we believe this reflects the absence of intestinal CYP1A1. Oral BaP-treated Cyp1a1/1a2/1b1(-/-) mice showed the same "rescued" response as that seen in the Cyp1a1/1b1(-/-) mouse; we believe this reflects the absence of CYP1B1 in immune tissues. Urinary metabolite profiles were dramatically different between untreated triple-knockout and wild-type; principal components analysis showed that the shifts in urinary metabolite patterns in oral BaP-treated triple-knockout and wild-type mice were also strikingly different. Liver microarray cDNA differential expression (comparing triple-knockout with wild-type) revealed at least 89 genes up- and 62 genes down-regulated (P-value < or = 0.00086). Gene Ontology "classes of genes" most perturbed in the untreated triple-knockout (compared with wild-type) include lipid, steroid, and cholesterol biosynthesis and metabolism; nucleosome and chromatin assembly; carboxylic and organic acid metabolism; metal-ion binding; and ion homeostasis. In the triple-knockout compared with the wild-type mice, response to zymosan-induced peritonitis was strikingly exaggerated, which may well reflect down-regulation of Socs2 expression. If a single common molecular pathway is responsible for all of these phenotypes, we suggest that functional effects of the loss of all three Cyp1 genes could be explained by perturbations in CYP1-mediated eicosanoid production, catabolism and activities.

Innate immune signaling is critical for the development of protective immunity. Such signaling is, perforce, tightly controlled. Lipoxins (LXs) are eicosanoid mediators that play key counterregulatory roles during infection. The molecular mechanisms underlying LX-mediated control of innate immune signaling are of interest. In this study, we show that LX and aspirin (ASA)-triggered LX (ATL) inhibit innate immune signaling by inducing suppressor of cytokine signaling (SOCS) 2–dependent ubiquitinylation and proteasome-mediated degradation of TNF receptor–associated factor (TRAF) 2 and TRAF6, which are adaptor molecules that couple TNF and interleukin-1 receptor/Toll-like receptor family members to intracellular signaling events. LX-mediated degradation of TRAF6 inhibits proinflammatory cytokine production by dendritic cells. This restraint of innate immune signaling can be ablated by inhibition of proteasome function. In vivo, this leads to dysregulated immune responses, accompanied by increased mortality during infection. Proteasomal degradation of TRAF6 is a central mechanism underlying LX-driven immune counterregulation, and a hitherto unappreciated mechanism of action of ASA. These findings suggest a new molecular target for drug development for diseases marked by dysregulated inflammatory responses.

Activation of Toll-like receptor (TLR) signaling by microbial and host molecular signatures is critical to the induction of immune responses. Such signaling is, perforce, kept under tight control. We recently discovered a novel endogenous inhibitor of TLR-4 — RP105. Initially identified as a B-cell-specific molecule with a role in B-cell proliferation in response to RP105 mAb and LPS, RP105 is a TLR-4 homologue. Further, like TLR-4 whose surface expression and signaling depends upon co-expression of the secreted protein MD-2, surface expression of RP105 is dependent upon co-expression of the MD2 homologue, MD-1. Unlike the TLRs, however, RP105 lacks a signaling domain, having the apparent structure of a TLR inhibitor. Further, RP105 is not B-cell-specific; its expression directly mirrors that of TLR-4 on dendritic cells and macrophages. These considerations suggested a role for RP105 as a physiological inhibitor of TLR-4 signaling. Indeed, we have recently found that: (i) RP105 is a specific inhibitor of TLR-4 signaling in HEK293 cells; (ii) RP105/MD-1 interacts directly with TLR-4/MD-2, inhibiting the ability of this signaling complex to bind LPS; (iii) RP105 regulates TLR-4 signaling in dendritic cells and macrophages; and (iv) RP105 regulates in vivo responses to LPS.

Four students at the James L. Winkle College of Pharmacy, accompanied by a faculty member, traveled to Tanzania on an elective ambulatory care advanced pharmacy practice experience rotation to learn, provide care, and implement a schistosomiasis project in the village of Burere. We were part of a

Although several subsets of intestinal APCs have been described, there has been no systematic evaluation of their phenotypes, functions, and regional localization to date. In this article, we used 10-color flow cytometry to define the major APC subsets in the small and large intestine lamina propria. Lamina propria APCs could be subdivided into CD11c+CD11b−, CD11c+CD11b+, and CD11cdullCD11b+ subsets. CD11c+CD11b− cells were largely CD103+F4/80− dendritic cells (DCs), whereas the CD11c+CD11b+ subset comprised CD11c+CD11b+CD103+F4/80− DCs and CD11c+CD11b+CD103−F4/80+ macrophage-like cells. The majority of CD11cdullCD11b+ cells were CD103−F4/80+ macrophages. Although macrophages were more efficient at inducing Foxp3+ regulatory T (Treg) cells than DCs, at higher T cell/APC ratios, all of the DC subsets efficiently induced Foxp3+ Treg cells. In contrast, only CD11c+CD11b+CD103+ DCs efficiently induced Th17 cells. Consistent with this, the regional distribution of CD11c+CD11b+CD103+ DCs correlated with that of Th17 cells, with duodenum > jejunum > ileum > colon. Conversely, CD11c+CD11b−CD103+ DCs, macrophages, and Foxp3+ Treg cells were most abundant in the colon and scarce in the duodenum. Importantly, however, the ability of DC and macrophage subsets to induce Foxp3+ Treg cells versus Th17 cells was strikingly dependent on the source of the mouse strain. Thus, DCs from C57BL/6 mice from Charles River Laboratories (that have segmented filamentous bacteria, which induce robust levels of Th17 cells in situ) were more efficient at inducing Th17 cells and less efficient at inducing Foxp3+ Treg cells than DCs from B6 mice from The Jackson Laboratory. Thus, the functional specializations of APC subsets in the intestine are dependent on the T cell/APC ratio, regional localization, and source of the mouse strain.

As all immune responses have potential for damaging the host, tight regulation of such responses—in amplitude, space, time and character—is essential for maintaining health and homeostasis. It was thus inevitable that the initial wave of papers on the role of Toll-like receptors (TLRs), NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs) in activating innate and adaptive immune responses would be followed by a second wave of reports focusing on the mechanisms responsible for restraining and modulating signaling by these receptors. This overview outlines current knowledge and controversies about the immunobiology of the RP105/MD-1 complex, a modulator of the most robustly signaling TLR, TLR4.

Functional analysis of the DNA regulatory regions that control gene expression has largely been performed through transient transfection of promoter–reporter constructs into transformed cells. However, transformed cells are often poor models of primary cells. To directly analyze DNA regulatory regions in primary cells, we generated a novel adenoviral luciferase reporter vector, pShuttle-luciferase-GFP (pSLUG) that contains a promoterless luciferase cassette (with an upstream cloning site) for probing promoter activity, and a GFP expression cassette that allows for the identification of transduced cells. Recombinant adenoviruses generated from this vector can transduce a wide range of primary immune cells with high efficiency, including human macrophages, dendritic cells and T cells; and mouse T cells transgenic for the coxsackie and adenoviral receptor (CAR). In primary T cells, we show inducible nuclear factor of activated T cells (NF-AT) activity using a recombinant pSLUG adenovirus containing a consensus NF-AT promoter. We further show inducible IL-12/23 p40 promoter activity in primary macrophages and dendritic cells using a recombinant pSLUG adenovirus containing the proximal human IL-12/23 p40 promoter. The pSLUG system promises to be a powerful tool for the analysis of DNA regulatory regions in diverse types of primary immune cells.

Activation of Toll-like receptor (TLR) signaling by microbial signatures is critical to the induction of immune responses. Such responses demand tight regulation. RP105 is a TLR homolog, thought to be largely B cell-specific, which lacks a signaling domain. We report that RP105 expression is wide, directly mirroring that of TLR4 on antigen presenting cells. We further show that RP105 is a specific inhibitor of TLR4 signaling in HEK293 cells, a function conferred by its extracellular domain. Notably, RP105 and its helper molecule, MD-1, interacted directly with the TLR4 signaling complex, inhibiting its ability to bind microbial ligand. Finally, we demonstrate that RP105 regulates TLR4 signaling in dendritic cells, as well as endotoxin responses in vivo. Thus, these results identify RP105 as a physiological negative regulator of TLR4 responses.

We found that a subset of CD11b+ myeloid cells in the intestinal lamina propria constitutively produce IL-10 mRNA, and adoptive transfer of these IL-10 producing cells to recipients helped to maintain Foxp3 expression and the function of Treg. Although much emphasis has been placed on the regulatory role of T cell derived IL-10, our data show that IL-10 synthesis by intestinal myeloid cells has a nonredundant and dramatic effect on maintaining Treg function and preventing T cell-mediated colitis in mice. Here, we further investigate the role of intestinal myeloid cell derived IL-10 in the regulation of gut inflammation. IL-10 producing intestinal myeloid cells expressed higher CD11b, CD11c, F4/80, Gr-1 and CX3CR1 messenger RNA and protein, compared to their non-IL-10 producing intestinal myeloid counterparts. Myeloid cell specific (LysM-Cre driven) IL-10 deficient mice had a similar Treg population in the large intestine compared to controls. C. rodentium infection caused a decrease in the number of Treg in the large intestine, but not in the spleen, and moreover, this defect was more pronounced in mice with a myeloid cell specific IL-10 deficiency. Inflammation in colitis models or following acute infections leads to decreased intestinal Treg. IL-10 producing myeloid cells has a role in maintaining the Treg population in the intestine under inflammatory conditions, as exemplified by C. rodentium infection.

Activated antigen-specific T cells produce a variety of effector molecules for clearing infection, but also contribute significantly to inflammation and tissue injury. Here we report an anti-inflammatory property of anti-viral CD8+ and CD4+ effector T cells (Te) in the infected periphery during acute pulmonary virus infection. We find that, during acute influenza and other respiratory virus infection, IL-10 is produced in the infected lungs at high levels -- exclusively by infiltrating virus-specific Te, with CD8+ Te contributing a larger fraction of the IL-10 produced. These Te in the periphery simultaneously produce IL-10 and proinflammatory cytokines, and express lineage markers characteristic of conventional Th/c1 cells. Importantly, blocking the action of the Te-derived IL-10 results in enhanced pulmonary inflammation and injury associated with the viral infection. Our results demonstrate that anti-viral Te exert regulatory functions -- that is, fine-tune the extent of lung inflammation/injury associated with respiratory virus infection by the production of an anti-inflammatory cytokine.