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Background & Aims A balance between effector and regulatory T-cell (Treg) responses is required to maintain intestinal homeostasis. To regulate immunity, T cells migrate to the intestine using a combination of adhesion molecules and chemokine receptors. However, it is not known whether the migration pathways of effector cells and Tregs are distinct or shared. We sought to determine whether interaction between the chemokine receptor 9 (CCR9) and its ligand, chemokine ligand 25 (CCL25), allows effectors or Tregs to localize to chronically inflamed small intestine. Methods By using a mouse model that develops Crohn's-like ileitis (tumor necrosis factor Δadenosine uracyl-rich element [TNFΔARE] mice) we examined the role of CCL25–CCR9 interactions for effector and Treg traffic using flow cytometry, quantitative reverse-transcription polymerase chain reaction, immunohistochemistry, immunoneutralization, and proliferation analyses. Results In TNFΔARE mice, expression of CCL25 and the frequency of CCR9-expressing lymphocytes increased during late-stage disease. In the absence of CCR9, TNFΔARE mice developed exacerbated disease, compared with their CCR9-sufficient counterparts, which coincided with a deficiency of CD4 + /CD25 + /forkhead box P3 + and CD8 + /CD103 + Tregs within the intestinal lamina propria and mesenteric lymph nodes. Furthermore, the CD8 + /CCR9 + subset decreased the proliferation of CD4 + T cells in vitro. Administration of a monoclonal antibody against CCR9 to TNFΔARE mice exacerbated ileitis in vivo, confirming the regulatory role of CD8 + /CCR9 + cells. Conclusions Signaling of the chemokine CCL25 through its receptor CCR9 induces Tregs to migrate to the intestine. These findings raise concerns about the development of reagents to disrupt this pathway for the treatment of patients with Crohn's disease.

TL1A is a member of the TNF superfamily and its expression is increased in the mucosa of inflammatory bowel disease patients. Moreover, a subset of Crohn's disease (CD) patients with the risk TL1A haplotype is associated with elevated TL1A expression and a more severe disease course. To investigate the in vivo role of elevated TL1A expression, we generated two transgenic (Tg) murine models with constitutive Tl1a expression in either lymphoid or myeloid cells. Compared to wildtype (WT) mice, constitutive expression of Tl1a in either lymphoid or myeloid cells showed mild patchy inflammation in the small intestine, which was more prominent in the ileum. In addition, mice with constitutive Tl1a expression exhibited enhanced intestinal and colonic fibrosis compared to WT littermates. The percentage of T cells expressing the gut homing chemokine receptors CCR9 and CCR10 was higher in the Tl1a Tg mice compared to WT littermates. Sustained expression of Tl1A in T cells also lead to increased Foxp3+ Treg cells. T cells or antigen presenting cells (APC) with constitutive expression of Tl1a were found to have a more activated phenotype and mucosal mononuclear cells exhibit enhanced Th1 cytokine activity. These results indicated an important role of TL1A in mucosal T cells and APC function and showed that up-regulation of TL1A expression can promote mucosal inflammation and gut fibrosis.

Rationale CD103+ DCs (dendritic cells) and CCR9+ pDCs (plasmacytoid DCs) have been implicated in promoting tolerance to antigens through regulatory-T cell induction. We have conducted food oral immunotherapy (OIT) clinical studies for the last 3 years at Stanford University. We hypothesized that subjects with food allergies have low CD103+ and CCR9+ expression on their DCs but that these DC populations change over time while on therapy.

whether colonic tissue-specific factors are responsible for re-educating DC into a gut-like phenotype. To address this issue we cultured human colonic biopsies from healthy controls and collected supernatants (SN) to condition human blood DC for 24 hours. RESULTS: Conditioning DC with SN generated In Vitro a human gut-like DC phenotype, characterized by a higher proportion of cells expressing the CCR9 (p=0.0017, n=11), β7 (p=0.0328, n=13) and CD103 (p=0.0354, n=10) gut-homingmarkers compared with their basal counterparts. A tolerogenic phenotype was also induced, characterized by reduced surface expression of the co-stimulatory markers CD40 (p=0.0297, n=9) and CD83 (p=0.0315, n=8), and also of TLR2 (p=0.0029, n=13) and TLR4 (p=0.0372, n=11). In addition, a regulatory intracellular DC cytokine profile was induced with reduced IL-12 and increased IL-10 production (n= 3). Furthermore, SN-conditioned DC demonstrated enhanced phagocytic properties (n=3), compared with those in basal conditions. These data demonstrate that human blood DC can be modulated to express the phenotype and function of human gut DC. Moreover, SNconditioned DC were less effective in stimulating proliferation of allogeneic T-cells, which subsequently expressed an increased gut/skin homing profile (n=3). CONCLUSION: We have demonstrated the relevance of the local tissue microenvironment in modulating DC since conditioning blood DC with colonic biopsy SN -through a mechanism in which vitamin A was revealed as essential but not sufficienthave the capacity to condition DC into gutlike DC with unique properties rendering them crucial for oral tolerance. Identifying all the molecules related to the generation of the tolerogenic gut-like DC would provide us with new targets for immunomodulation in patients suffering from IBD, where the functionality of gut-DC is altered leading to a lack of oral tolerance against the commensal microbiota.

Introduction: Monocytes/macrophages accumulate in the rheumatoid (RA) synovium where they play a central role in inflammation and joint destruction. Identification of molecules involved in their accumulation and differentiation is important to inform therapeutic strategies. This study investigated the expression and function of chemokine receptor CCR9 in the peripheral blood (PB) and synovium of RA, non-RA patients and healthy volunteers. Methods: CCR9 expression on PB monocytes/macrophages was analysed by flow cytometry and in synovium by immunofluorescence. Chemokine receptor CCR9 mRNA expression was examined in RA and non-RA synovium, monocytes/macrophages from PB and synovial fluid (SF) of RA patients and PB of healthy donors using the reverse transcription polymerase chain reaction (RT-PCR). Monocyte differentiation and chemotaxis to chemokine ligand 25 (CCL25)/TECK were used to study CCR9 function. Results: CCR9 was expressed by PB monocytes/macrophages in RA and healthy donors, and increased in RA. In RA and non-RA synovia, CCR9 co-localised with cluster of differentiation 14+ (CD14+) and cluster of differentiation 68+ (CD68+) macrophages, and was more abundant in RA synovium. CCR9 mRNA was detected in the synovia of all RA patients and in some non-RA controls, and monocytes/macrophages from PB and SF of RA and healthy controls. CCL25 was detected in RA and non-RA synovia where it co-localised with CD14+ and CD68+ cells. Tumour necrosis factor alpha (TNFa) increased CCR9 expression on human acute monocytic leukemia cell line THP1 monocytic cells. CCL25 induced a stronger monocyte differentiation in RA compared to healthy donors. CCL25 induced significant chemotaxis of PB monocytes but not consistently among individuals. Conclusions: CCR9 expression by monocytes is increased in RA. CCL25 may be involved in the differentiation of monocytes to macrophages particularly in RA.

Host dendritic cells (DCs) play a critical role in initiating graft versus host disease (GVHD) and graft versus leukemia (GVL), and separation of GVL from GVHD remains a major challenge in the treatment of hematological malignancies by allogeneic hematopoietic cell transplantation (HCT). Here, we show that preconditioning with anti- CD3 mAb before conditioning with total body irradiation prevents GVHD but retains GVL in a HCT model of MHC-mismatched C57BL/6 donor to BALB/c host. Prevention of GVHD is associated with inhibition of donor T expression of homing and chemokine receptors and inhibition of GVHD target tissue expression of chemokines. Furthermore, inhibition of donor T expression of gut homing a4b7 and chemokine receptor CCR9 by anti-CD3 preconditioning results from reduction of CD103+ DCs in draining mesenteric lymph nodes, which is associated with downregulation of DC expression of CCR7, a receptor required for tissue DC migration to draining LN. These results indicate that anti-CD3 preconditioning reduces not only tissue release of chemokines but also prevents tissue DC migration to draining LN and subsequently reduces draining LN DC’s capacity in imprinting donor T tissue tropism. Therefore, modulation of host DCs by anti-CD3 preconditioning before HCT represents a new approach for separating GVL from GVHD. (Li and Chen contribute equally.

Memory CD4+ T cells express characteristic adhesion molecules and chemokine receptors that dictate their recirculation to the tissue in which they first encountered antigen. On page 1045, Baekkevold and colleagues show that T cells may compete for access to the skin and only gain entry if they express the CC-chemokine receptor-4 (CCR4). Previous studies showed that skin-homing and gut-homing CD4+ T cells express distinct chemokine receptors—CCR4 for skin-homing cells and CCR9 for gut-homing cells—and this was mirrored by the expression of the corresponding chemokine ligand in local blood vessels. The authors thus proposed that expression of CCR4 was required for T cells to access the skin (and CCR9 for the gut) but were perplexed by the phenotype of CCR4-deficient mice, which had normal numbers of skin-homing T cells. Another skin-specific chemokine receptor may have compensated for the absence of CCR4. To test this, Baekkevold et al. staged a competition between wild type and CCR4-deficient bone marrow cells in lymphocyte-deficient mice. They found that CCR4+ cells were highly enriched among lymphocytes that trafficked to the skin, particularly during skin inflammation. This suggested that CCR4, although not essential, facilitated the generation of the skin-homing memory T cell population. Recent studies have shown that tissue-specific dendritic cells (DC) impart CD8+ T cells with specific homing instructions and the authors suspect that a DC-derived signal may trigger CCR4 expression and similarly instruct CD4+ T cells.

The intestinal barrier, one of the first targets of HIV/simian immunodeficiency virus (SIV) is subjected to major physiological changes during acute infection. Having previously shown that pharmaceutical injection of interleukin-7 (IL-7) triggers chemokine expression in many organs leading to massive T-cell homing, in particular to the intestine, we here explored mucosal IL-7 expression as part of the cytokine storm occurring during the acute phase of SIV infection in rhesus macaques. Quantifying both mRNA and protein in tissues, we demonstrated a transient increase of IL-7 expression in the small intestine of SIV-infected rhesus macaques, starting with local detection of the virus by day 3 of infection. We also observed increased transcription levels of several chemokines in the small intestine. In infected macaques, ileal IL-7 expression correlated with the transcription of four of these chemokines. Among these chemokines, the macrophage and/or T-cell attractant chemokines CCL4, CCL25, and CCL28 also demonstrated increased transcription in uninfected IL-7-treated monkeys. Through immunohistofluorescence staining and image analysis, we observed increased CD8+ T-cell numbers and stable CD4+ T-cell counts in the infected lamina propria (LP) during hyperacute infection. Concomitantly, circulating CCR9+beta7+ CD4+ and CD8+ T-cells dropped during acute infection, suggesting augmented intestinal homing of gut-imprinted T-cells. Finally, CD4+ macrophages transiently decreased in the submucosa and concentrated in the LP during the first days of infection. Overall, our study identifies IL-7 as a danger signal in the small intestine of Chinese rhesus macaques in response to acute SIV infection. Through stimulation of local chemokine expressions, this overexpression of IL-7 triggers immune cell recruitment to the gut. These findings suggest a role for IL-7 in the initiation of early mucosal immune responses to SIV and HIV infections. However, IL-7 triggered CD4+ T-cells and macrophages localization at viral replication sites could also participate to viral spread and establishment of viral reservoirs.

Background The CC chemokine receptor 9 (CCR9) plays an important role in tumorigenesis and metastasis in various cancers. Our previous studies have shown the aberrant expression of CCR9 in non-small cell lung cancer (NSCLC) cell lines, revealing that the CCR9-CCL25 axis modulates cell migration and invasion, and supports cancer cell survival by inhibiting apoptosis in vitro and in vivo. In the present study, we aimed to evaluate the expression and possible prognostic role of CCR9 in lung adenocarcinoma. Methods Immunohistochemical analysis of CCR9 expression was performed on 144 lung adenocarcinoma tissues and 30 adjacent normal lung parenchymal tissues. We assessed the correlation of CCR9 expression with clinicopathological characteristics and the prognosis of lung adenocarcinoma. Results The expression of CCR9 was increased in lung adenocarcinoma tissue compared with normal lung tissue. Moreover, such an expression was positively correlated with tumor size (p = 0.032), lymph node metastasis (p = 0.002) and advanced TNM stage (p = 0.012). In addition, the patients with negative CCR9 expression exhibited a higher overall survival (OS) compared with those with positive CCR9 expression. Multivariate analysis showed that the CCR9 expression was an independent prognostic factor for the OS of patients with lung adenocarcinoma. Conclusions We, for the first time, reported that CCR9 could be beneficial in predicting lymph node metastasis, and it might act as a novel prognostic biomarker for lung adenocarcinoma.

Background Chemokine therapy with C–C motif chemokine ligand 25 (CCL25) is currently under investigation as a promising approach to treat articular cartilage degeneration. We developed a delayed release mechanism based on Poly (lactic-co-glycolic acid) (PLGA) microparticle encapsulation for intraarticular injections to ensure prolonged release of therapeutic dosages. However, CCL25 plays an important role in immune cell regulation and inflammatory processes like T-cell homing and chronic tissue inflammation. Therefore, the potential of CCL25 to activate immune cells must be assessed more thoroughly before further translation into clinical practice. The aim of this study was to evaluate the reaction of different immune cell subsets upon stimulation with different dosages of CCL25 in comparison to CCL25 released from PLGA particles. Results Immune cell subsets were treated for up to 5 days with CCL25 and subsequently analyzed regarding their cytokine secretion, surface marker expression, polarization, and migratory behavior. The CCL25 receptor C–C chemokine receptor type 9 (CCR9) was expressed to a different extent on all immune cell subsets. Direct stimulation of peripheral blood mononuclear cells (PBMCs) with high dosages of CCL25 resulted in strong increases in the secretion of monocyte chemoattractant protein-1 (MCP-1), interleukin-8 (IL-8), interleukin-1β (IL-1β), tumor-necrosis-factor-α (TNF-α) and interferon-γ (IFN-γ), upregulation of human leukocyte antigen-DR (HLA-DR) on monocytes and CD4+ T-cells, as well as immune cell migration along a CCL25 gradient. Immune cell stimulation with the supernatants from CCL25 loaded PLGA microparticles caused moderate increases in MCP-1, IL-8, and IL-1β levels, but no changes in surface marker expression or migration. Both CCL25-loaded and unloaded PLGA microparticles induced an increase in IL-8 and MCP-1 release in PBMCs and macrophages, and a slight shift of the surface marker profile towards the direction of M2-macrophage polarization. Conclusions While supernatants of CCL25 loaded PLGA microparticles did not provoke strong inflammatory reactions, direct stimulation with CCL25 shows the critical potential to induce global inflammatory activation of human leukocytes at certain concentrations. These findings underline the importance of a safe and reliable release system in a therapeutic setup. Failure of the delivery system could result in strong local and systemic inflammatory reactions that could potentially negate the benefits of chemokine therapy.

Human regulatory T cells (Treg) are important in immune regulation, but also show plasticity in specific settings. CD161 expression identifies effector-like Treg. Here we determined how CD161+ Treg relate to CD161+ conventional T cells (Tconv). Transcriptional profiling identified a shared transcriptional signature between CD161+ Tconv and CD161+ Treg, which is associated with Th1 and Th17 cells, and tissue homing, including high expression of gut homing receptors. Upon retinoic acid (RA) exposure, CD161+ T cells were more enriched for CCR9+ and integrin α4+β7+ cells than CD161- T cells. In addition, CD161+ Tconv and CD161+ Treg were enriched at the inflamed site in autoimmune arthritis, and CD161+ and CD161- Treg from the inflamed site showed suppressive capacity. CD161+ T cells from the site of autoimmune arthritis showed a diminished gut homing phenotype and blunted response to RA suggesting prior imprinting by RA in the gut or at peripheral sites rather than during synovial inflammation. TCRβ repertoires of CD161+ and CD161- Tconv and Treg from blood showed limited overlap whereas there was clear overlap between CD161+ and CD161- Tconv, and CD161+ and CD161- Treg from the inflamed site suggesting that the inflamed environment may alter CD161 levels, potentially contributing to disease pathogenesis.

Understanding how memory B cells are induced and relate to long-lived plasma cells is important for vaccine development. Immunity to oral vaccines has been considered short-lived because of a poor ability to develop IgA B-cell memory. Here we demonstrate that long-lived mucosal IgA memory is readily achieved by oral but not systemic immunization in mouse models with NP hapten conjugated with cholera toxin and transfer of B1-8high/GFP+ NP-specific B cells. Unexpectedly, memory B cells are poorly related to long-lived plasma cells and less affinity-matured. They are α4β7-integrin+CD73+PD-L2+CD80+ and at systemic sites mostly IgM+, while 80% are IgA+ in Peyer’s patches. On reactivation, most memory B cells in Peyer’s patches are GL7−, but expand in germinal centres and acquire higher affinity and more mutations, demonstrating strong clonal selection. CCR9 expression is found only in Peyer’s patches and appears critical for gut homing. Thus, gut mucosal memory possesses unique features not seen after systemic immunization.

Introduction Guided migration of chondrogenically differentiated cells has not been well studied, even though it may be critical for growth, repair, and regenerative processes. The chemokine CCL25 is believed to play a critical role in the directional migration of leukocytes and stem cells. To investigate the motility effect of serum- or CCL25-mediated chemotaxis on chondrogenically differentiated cells, mesenchymal stem cells (MSCs) were induced to chondrogenic lineage cells. Methods MSC-derived chondrogenically differentiated cells were characterized for morphology, histology, immunohistochemistry, quantitative polymerase chain reaction (qPCR), surface profile, and serum- or CCL25-mediated cell migration. Additionally, the chemokine receptor, CCR9, was examined in different states of MSCs. Results The chondrogenic differentiated state of MSCs was positive for collagen type II and Alcian blue staining, and showed significantly upregulated expression of COL2A1and SOX9, and downregulated expression of CD44, CD73, CD90, CD105 and CD166, in contrast to the undifferentiated and dedifferentiated states of MSCs. For the chondrogenic differentiated, undifferentiated, and dedifferentiated states of MSCs, the serum-mediated chemotaxis was in a percentage ratio of 33%:84%:85%, and CCL25-mediated chemotaxis was in percentage ratio of 12%:14%:13%, respectively. On the protein level, CCR9, receptor of CCL25, was expressed in the form of extracellular and intracellular domains. On the gene level, qPCR confirmed the expression of CCR9 in different states of MSCs. Conclusions CCL25 is an effective cue to guide migration in a directional way. In CCL25-mediated chemotaxis, the cell-migration rate was almost the same for different states of MSCs. In serum-mediated chemotaxis, the cell-migration rate of chondrogenically differentiated cells was significantly lower than that in undifferentiated or dedifferentiated cells. Current knowledge of the surface CD profile and cell migration could be beneficial for regenerative cellular therapies.

Modulation of the expression of chemokines and chemokine receptors in whole blood was compared following infection of pigs with high and low virulence isolates of African swine fever virus. Levels of mRNAs for CCL2, CCL3L1, CCL4, CXCL10, CCR1 and CCR5 were significantly increased in at least one time point following infection in two experiments and CCL5, CCR9 and CXCR4 mRNA were significantly increased in one of the experiments. The results showed that greatest fold increases in mRNAs for CXCL10 and CCL2 were observed following infection of pigs. CXCL10 mRNA was increased by up to 15 fold in infected compared to uninfected pigs. CXCL10 protein was also detected in serum from pigs infected with the high virulence Benin 97/1 isolate. Levels of CCL2 mRNA were increased in pigs infected with high virulence Benin 97/1 isolate compared to low virulence OURT88/3 isolate and this correlated with an increase of greater than 30 fold in levels of CCL2 protein detected in serum from pigs infected with this isolate. An increase in overall chemotaxis active compounds in defibrinated plasma samples from Benin 97/1 infected pigs was observed at 3 days post-infection (dpi) and a decrease by 7 dpi as measured by chemotaxis assay using normal pig leucocytes in vitro. Increased levels of CXCL10 may either contribute to the activation of lymphocyte priming toward the Th1 phenotype or induction of T lymphocyte apoptosis. Increased levels of CCL2, a chemoattractant for macrophages, may result in increased recruitment of monocytes from bone marrow thus increasing the pool of cells susceptible to infection.