Lymphocyte CC chemokine receptor 9 and epithelial thymus-expressed chemokine (TECK) expression distinguish the small intestinal immune compartment: Epithelial expression of tissue-specific chemokines as an organizing principle in regional immunity

Mechanisms of T cell organotropism

Protective immunity relies upon T cell differentiation and subsequent migration to target tissues. Similarly, immune homeostasis requires the localization of regulatory T cells (Tregs) to the sites where immunity takes place. While naïve T lymphocytes recirculate predominantly in secondary lymphoid tissue, primed T cells and activated Tregs must traffic to the antigen rich non-lymphoid tissue to exert effector and regulatory responses, respectively. Following priming in draining lymph nodes, T cells acquire the 'homing receptors' to facilitate their access to specific tissues and organs. An additional level of topographic specificity is provided by T cells receptor recognition of antigen displayed by the endothelium. Furthermore, co-stimulatory signals (such as those induced by CD28) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response. We here review the molecular mechanisms supporting trafficking of both effector and regulatory T cells to specific antigen-rich tissues.

Toll-like receptor 4-mediated lymphocyte influx induces neonatal necrotizing enterocolitis

The nature and role of the intestinal leukocytes in necrotizing enterocolitis (NEC), a severe disease affecting premature infants, remain unknown. We now show that the intestine in mouse and human NEC is rich in lymphocytes that are required for NEC development, as recombination activating gene 1–deficient (Rag1–/–) mice were protected from NEC and transfer of intestinal lymphocytes from NEC mice into naive mice induced intestinal inflammation. The intestinal expression of the lipopolysaccharide receptor TLR4, which is higher in the premature compared with full-term human and mouse intestine, is required for lymphocyte influx through TLR4-mediated upregulation of CCR9/CCL25 signaling. TLR4 also mediates a STAT3-dependent polarization toward increased proinflammatory CD3+CD4+IL-17+ and reduced tolerogenic Foxp3+ Treg lymphocytes (Tregs). Th17 lymphocytes were required for NEC development, as inhibition of STAT3 or IL-17 receptor signaling attenuated NEC in mice, while IL-17 release impaired enterocyte tight junctions, increased enterocyte apoptosis, and reduced enterocyte proliferation, leading to NEC. Importantly, TLR4-dependent Th17 polarization could be reversed by the enteral administration of retinoic acid, which induced Tregs and decreased NEC severity. These findings identify an important role for proinflammatory lymphocytes in NEC development via intestinal epithelial TLR4 that could be reversed through dietary modification.

Modulation of liver tolerance by conventional and nonconventional antigen-presenting cells and regulatory immune cells

The liver is a tolerogenic organ with exquisite mechanisms of immune regulation that ensure upkeep of local and systemic immune tolerance to self and foreign antigens, but that is also able to mount effective immune responses against pathogens. The immune privilege of liver allografts was recognized first in pigs in spite of major histo-compatibility complex mismatch, and termed the "liver tolerance effect". Furthermore, liver transplants are spontaneously accepted with only low-dose immunosuppression, and induce tolerance for non-hepatic co-transplanted allografts of the same donor. Although this immunotolerogenic environment is favorable in the setting of organ transplantation, it is detrimental in chronic infectious liver diseases like hepatitis B or C, malaria, schistosomiasis or tumorigenesis, leading to pathogen persistence and weak anti-tumor effects. The liver is a primary site of T-cell activation, but it elicits poor or incomplete activation of T cells, leading to their abortive activation, exhaustion, suppression of their effector function and early death. This is exploited by pathogens and can impair pathogen control and clearance or allow tumor growth. Hepatic priming of T cells is mediated by a number of local conventional and nonconventional antigen-presenting cells (APCs), which promote tolerance by immune deviation, induction of T-cell anergy or apoptosis, and generating and expanding regulatory T cells. This review will focus on the communication between classical and nonclassical APCs and lymphocytes in the liver in tolerance induction and will discuss recent insights into the role of innate lymphocytes in this process.

Intestinal CCL25 expression is increased in colitis and correlates with inflammatory activity

CCL25-mediated activation of CCR9 is critical for mucosal lymphocyte recruitment to the intestine. In immune-mediated liver injury complicating inflammatory bowel disease, intrahepatic activation of this pathway allows mucosal lymphocytes to be recruited to the liver, driving hepatobiliary destruction in primary sclerosing cholangitis (PSC). However, in mice and healthy humans CCL25 expression is restricted to the small bowel, whereas few data exist on activation of this pathway in the inflamed colon despite the vast majority of PSC patients having ulcerative colitis. Herein, we show that colonic CCL25 expression is not only upregulated in patients with active colitis, but strongly correlates with endoscopic Mayo score and mucosal TNFα expression. Moreover, approximately 90% (CD4(+)) and 30% (CD8(+)) of tissue-infiltrating T-cells in colitis were identified as CCR9(+) effector lymphocytes, compared to <10% of T-cells being CCR9(+) in normal colon. Sorted CCR9(+) lymphocytes also demonstrated enhanced cellular adhesion to stimulated hepatic sinusoidal endothelium compared with their CCR9(-) counterparts when under flow. Collectively, these results suggest that CCR9/CCL25 interactions are not only involved in colitis pathogenesis but also correlate with colonic inflammatory burden; further supporting the existence of overlapping mucosal lymphocyte recruitment pathways between the inflamed colon and liver.

Glucocorticoids Suppress CCR9-Mediated Chemotaxis, Calcium Flux, and Adhesion to MAdCAM-1 in Human T Cells

CCR9 expressed on T lymphocytes mediates migration to the small intestine in response to a gradient of CCL25. CCL25-stimulated activation of α4β7 integrin promotes cell adherence to mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expressed by vascular endothelial cells of the intestine, further mediating gut-specific homing. Inflammatory bowel disease is a chronic inflammatory condition that primarily affects the gastrointestinal tract and is characterized by leukocyte infiltration. Glucocorticoids (GCs) are widely used to treat inflammatory bowel disease but their effect on intestinal leukocyte homing is not well understood. We investigated the effect of GCs on the gut-specific chemokine receptor pair, CCR9 and CCL25. Using human peripheral blood-derived T lymphocytes enriched for CCR9 by cell sorting or culturing with all-trans retinoic acid, we measured chemotaxis, intracellular calcium flux, and α4β7-mediated cell adhesion to plate-bound MAdCAM-1. Dexamethasone (DEX), a specific GC receptor agonist, significantly reduced CCR9-mediated chemotaxis and adhesion to MAdCAM-1 without affecting CCR9 surface expression. In contrast, in the same cells, DEX increased CXCR4 surface expression and CXCL12-mediated signaling and downstream functions. The effects of DEX on human primary T cells were reversed by the GC receptor antagonist mifepristone. These results demonstrate that GCs suppress CCR9-mediated chemotaxis, intracellular calcium flux, and α4β7-mediated cell adhesion in vitro, and these effects could contribute to the efficacy of GCs in treating intestinal inflammation in vivo.

A New Series of Orally Bioavailable Chemokine Receptor 9 (CCR9) Antagonists; Possible Agents for the Treatment of Inflammatory Bowel Disease

Chemokine receptor 9 (CCR9), a cell surface chemokine receptor which belongs to the G protein-coupled receptor, 7-trans-membrane superfamily, is expressed on lymphocytes in the circulation and is the key chemokine receptor that enables these cells to target the intestine. It has been proposed that CCR9 antagonism represents a means to prevent the aberrant immune response of inflammatory bowel disease in a localized and disease specific manner and one which is accessible to small molecule approaches. One possible reason why clinical studies with vercirnon, a prototype CCR9 antagonist, were not successful may be due to a relatively poor pharmacokinetic (PK) profile for the molecule. We wish to describe work aimed at producing new, orally active CCR9 antagonists based on the 1,3-dioxoisoindoline skeleton. This study led to a number of compounds that were potent in the nanomolar range and which, on optimization, resulted in several possible preclinical development candidates with excellent PK properties.

Leukocyte Trafficking to the Small Intestine and Colon

Leukocyte trafficking to the small and large intestines is tightly controlled to maintain intestinal immune homeostasis, mediate immune responses, and regulate inflammation. A wide array of chemoattractants, chemoattractant receptors, and adhesion molecules expressed by leukocytes, mucosal endothelium, epithelium, and stromal cells controls leukocyte recruitment and microenvironmental localization in intestine and in the gut-associated lymphoid tissues (GALTs). Naive lymphocytes traffic to the gut-draining mesenteric lymph nodes where they undergo antigen-induced activation and priming; these processes determine their memory/effector phenotypes and imprint them with the capacity to migrate via the lymph and blood to the intestines. Mechanisms of T-cell recruitment to GALT and of T cells and plasmablasts to the small intestine are well described. Recent advances include the discovery of an unexpected role for lectin CD22 as a B-cell homing receptor GALT, and identification of the orphan G-protein-coupled receptor 15 (GPR15) as a T-cell chemoattractant/trafficking receptor for the colon. GPR15 decorates distinct subsets of T cells in mice and humans, a difference in species that could affect translation of the results of mouse colitis models to humans. Clinical studies with antibodies to integrin α4β7 and its vascular ligand mucosal vascular addressin cell adhesion molecule 1 are proving the value of lymphocyte trafficking mechanisms as therapeutic targets for inflammatory bowel diseases. In contrast to lymphocytes, cells of the innate immune system express adhesion and chemoattractant receptors that allow them to migrate directly to effector tissue sites during inflammation. We review the mechanisms for innate and adaptive leukocyte localization to the intestinal tract and GALT, and discuss their relevance to human intestinal homeostasis and inflammation.

A high-throughput RNAi screen for detection of immune-checkpoint molecules that mediate tumor resistance to cytotoxic T lymphocytes

The success of T cell-based cancer immunotherapy is limited by tumor's resistance against killing by cytotoxic T lymphocytes (CTLs). Tumor-immune resistance is mediated by cell surface ligands that engage immune-inhibitory receptors on T cells. These ligands represent potent targets for therapeutic inhibition. So far, only few immune-suppressive ligands have been identified. We here describe a rapid high-throughput siRNA-based screening approach that allows a comprehensive identification of ligands on human cancer cells that inhibit CTL-mediated tumor cell killing. We exemplarily demonstrate that CCR9, which is expressed in many cancers, exerts strong immune-regulatory effects on T cell responses in multiple tumors. Unlike PDL1, which inhibits TCR signaling, CCR9 regulates STAT signaling in T cells, resulting in reduced T-helper-1 cytokine secretion and reduced cytotoxic capacity. Moreover, inhibition of CCR9 expression on tumor cells facilitated immunotherapy of human tumors by tumor-specific T cells in vivo. Taken together, this method allows a rapid and comprehensive determination of immune-modulatory genes in human tumors which, as an entity, represent the ‘immune modulatome’ of cancer.

Migration and Tissue Tropism of Innate Lymphoid Cells

Innate lymphoid cell (ILCs) subsets differentially populate various barrier and non-barrier tissues, where they play important roles in tissue homeostasis and tissue-specific responses to pathogen attack. Recent findings have provided insight into the molecular mechanisms that guide ILC migration into peripheral tissues, revealing common features among different ILC subsets as well as important distinctions. Recent studies have also highlighted the impact of tissue-specific cues on ILC migration, and the importance of the local immunological milieu. We review these findings here and discuss how the migratory patterns and tissue tropism of different ILC subsets relate to the development and differentiation of these cells, and to ILC-mediated tissue-specific regulation of innate and adaptive immune responses. In this context we outline open questions and important areas of future research.

Current stage in inflammatory bowel disease: What is next?

In recent years, the incidence of inflammatory bowel disease (IBD) has been on the rise, extending to countries where it was infrequent in the past. As a result, the gap between high and low incidence countries is decreasing. The disease, therefore, has an important economic impact on the healthcare system. Advances in recent years in pharmacogenetics and clinical pharmacology have allowed for the development of treatment strategies adjusted to the patient profile. Concurrently, new drugs aimed at inflammatory targets have been developed that may expand future treatment options. This review examines advances in the optimization of existing drug treatments and the development of novel treatment options for IBD.

Chemokine Receptor Expression on Normal Blood CD56(+) NK-Cells Elucidates Cell Partners That Comigrate during the Innate and Adaptive Immune Responses and Identifies a Transitional NK-Cell Population

Studies of chemokine receptors (CKR) in natural killer- (NK-) cells have already been published, but only a few gave detailed information on its differential expression on blood NK-cell subsets. We report on the expression of the inflammatory and homeostatic CKR on normal blood CD56(+low) CD16(+) and CD56(+high)  CD16(-/+low) NK-cells. Conventional CD56(+low) and CD56(+high) NK-cells present in the normal PB do express CKR for inflammatory cytokines, although with different patterns CD56(+low) NK-cells are mainly CXCR1/CXCR2(+) and CXCR3/CCR5(-/+), whereas mostly CD56(+high) NK-cells are CXCR1/CXCR2(-) and CXCR3/CCR5(+). Both NK-cell subsets have variable CXCR4 expression and are CCR4(-) and CCR6(-). The CKR repertoire of the CD56(+low) NK-cells approaches to that of neutrophils, whereas the CKR repertoire of the CD56(+high) NK-cells mimics that of Th1(+) T cells, suggesting that these cells are prepared to migrate into inflamed tissues at different phases of the immune response. In addition, we describe a subpopulation of NK-cells with intermediate levels of CD56 expression, which we named CD56(+int) NK-cells. These NK-cells are CXCR3/CCR5(+), they have intermediate levels of expression of CD16, CD62L, CD94, and CD122, and they are CD57(-) and CD158a(-). In view of their phenotypic features, we hypothesize that they correspond to a transitional stage, between the well-known CD56(+high) and CD56(+low) NK-cells populations.

Mucosal Immune Responses to Escherichia coli and Salmonella Infections

The best-characterized mucosa-associated lymphoid tissue (MALT), and also the most relevant for this review, is the gastrointestinal-associated lymphoid tissue (GALT). The review reviews our understanding of the importance of mucosal immune responses in resisting infections caused by E. coli and Salmonella spp. It focuses on the major human E. coli infections and discusses whether antigen-specific mucosal immune responses are important for resistance against primary infection or reinfection by pathogenic E. coli. It analyzes human data on mucosal immunity against E. coli, a growing body of data of mucosal responses in food production animals and other natural hosts of E. coli, and more recent experimental studies in mice carrying defined deletions in genes encoding specific immunological effectors, to show that there may be considerable conservation of the effective host mucosal immune response against this pathogen. The species Salmonella enterica contains a number of serovars that include pathogens of both humans and animals; these bacteria are frequently host specific and may cause different diseases in different hosts. Ingestion of various Salmonella serovars, such as Typhimurium, results in localized infections of the small intestine leading to gastroenteritis in humans, whereas ingestion of serovar Typhi results in systemic infection and enteric fever. Serovar Typhi infects only humans, and the review discusses the mucosal immune responses against serovar Typhi, focusing on the responses in humans and in the mouse typhoid fever model.

CCR9 Antagonists in the Treatment of Ulcerative Colitis

While it has long been established that the chemokine receptor CCR9 and its ligand CCL25 are essential for the movement of leukocytes into the small intestine and the development of small-intestinal inflammation, the role of this chemokine-receptor pair in colonic inflammation is not clear. Toward this end, we compared colonic CCL25 protein levels in healthy individuals to those in patients with ulcerative colitis. In addition, we determined the effect of CCR9 pharmacological inhibition in the mdr1a^−/− mouse model of ulcerative colitis. Colon samples from patients with ulcerative colitis had significantly higher levels of CCL25 protein compared to healthy controls, a finding mirrored in the mdr1a^−/− mice. In the mdr1a^−/− mice, CCR9 antagonists significantly decreased the extent of wasting and colonic remodeling and reduced the levels of inflammatory cytokines in the colon. These findings indicate that the CCR9:CCL25 pair plays a causative role in ulcerative colitis and suggest that CCR9 antagonists will provide a therapeutic benefit in patients with colonic inflammation.

Tissue instruction for migration and retention of TRM cells

During infection, a subset of effector T cells seeds the lymphoid and non-lymphoid tissues and gives rise to tissue-resident memory T cells (TRM). Recent findings have provided insight into the molecular and cellular mechanisms underlying tissue instruction of TRM cell homing, as well as the programs involved in their retention and maintenance. We review these findings here, highlighting both common features and distinctions between CD4 TRM and CD8 TRM cells. In this context we examine the role of memory lymphocyte clusters (MLCs), and propose that the MLCs serve as an immediate response center consisting of TRM cells on standby, capable of detecting incoming pathogens and mounting robust local immune responses to contain and limit the spread of infectious agents.

Interferon-γ Promotes Inflammation and Development of T-Cell Lymphoma in HTLV-1 bZIP Factor Transgenic Mice

Human T-cell leukemia virus type 1 (HTLV-1) is an etiological agent of several inflammatory diseases and a T-cell malignancy, adult T-cell leukemia (ATL). HTLV-1 bZIP factor (HBZ) is the only viral gene that is constitutively expressed in HTLV-1-infected cells, and it has multiple functions on T-cell signaling pathways. HBZ has important roles in HTLV-1-mediated pathogenesis, since HBZ transgenic (HBZ-Tg) mice develop systemic inflammation and T-cell lymphomas, which are similar phenotypes to HTLV-1-associated diseases. We showed previously that in HBZ-Tg mice, HBZ causes unstable Foxp3 expression, leading to an increase in regulatory T cells (Tregs) and the consequent induction of IFN-γ-producing cells, which in turn leads to the development of inflammation in the mice. In this study, we show that the severity of inflammation is correlated with the development of lymphomas in HBZ-Tg mice, suggesting that HBZ-mediated inflammation is closely linked to oncogenesis in CD4+ T cells. In addition, we found that IFN-γ-producing cells enhance HBZ-mediated inflammation, since knocking out IFN-γ significantly reduced the incidence of dermatitis as well as lymphoma. Recent studies show the critical roles of the intestinal microbiota in the development of Tregs in vivo. We found that even germ-free HBZ-Tg mice still had an increased number of Tregs and IFN-γ-producing cells, and developed dermatitis, indicating that an intrinsic activity of HBZ evokes aberrant T-cell differentiation and consequently causes inflammation. These results show that immunomodulation by HBZ is implicated in both inflammation and oncogenesis, and suggest a causal connection between HTLV-1-associated inflammation and ATL.

Mucosal vaccines: novel strategies and applications for the control of pathogens and tumors at mucosal sites

The mucosal immune system displays several adaptations reflecting the exposure to the external environment. The efficient induction of mucosal immune responses also requires specific approaches, such as the use of appropriate administration routes and specific adjuvants and/or delivery systems. In contrast to vaccines delivered via parenteral routes, experimental, and clinical evidences demonstrated that mucosal vaccines can efficiently induce local immune responses to pathogens or tumors located at mucosal sites as well as systemic response. At least in part, such features can be explained by the compartmentalization of mucosal B and T cell populations that play important roles in the modulation of local immune responses. In the present review, we discuss molecular and cellular features of the mucosal immune system as well as novel immunization approaches that may lead to the development of innovative and efficient vaccines targeting pathogens and tumors at different mucosal sites.

Retinoic Acid Differentially Regulates the Migration of Innate Lymphoid Cell Subsets to the Gut

Distinct groups of innate lymphoid cells (ILCs) such as ILC1, ILC2, and ILC3 populate the intestine, but how these ILCs develop tissue tropism for this organ is unclear. We report that prior to migration to the intestine ILCs first undergo a "switch" in their expression of homing receptors from lymphoid to gut homing receptors. This process is regulated by mucosal dendritic cells and the gut-specific tissue factor retinoic acid (RA). This change in homing receptors is required for long-term population and effector function of ILCs in the intestine. Only ILC1 and ILC3, but not ILC2, undergo the RA-dependent homing receptor switch in gut-associated lymphoid tissues. In contrast, ILC2 acquire gut homing receptors in a largely RA-independent manner during their development in the bone marrow and can migrate directly to the intestine. Thus, distinct programs regulate the migration of ILC subsets to the intestine for regulation of innate immunity.

Primary sclerosing cholangitis: a clinical update

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a progressive cholestatic disorder that ultimately can lead to cirrhosis, liver failure, malignancy and death. It is strongly associated with inflammatory bowel disease (IBD), and though a rare disease, its incidence is increasing. There are no proven medical therapies for PSC.

SOURCES OF DATA

Ovid Medline was utilised to search for articles with keywords 'sclerosing cholangitis' and 'cholangiocarcinoma' and containing titles 'primary sclerosing cholangitis', and references of these papers were cross-referenced for further relevant manuscripts.

AREAS OF AGREEMENT

PSC is a rare disease, and there is a strong association with risk loci within the major histocompatibility complex and other genes common to other autoimmune diseases. PSC is a premalignant condition, associated with higher rates of hepatobiliary and colorectal cancer in patients with ulcerative colitis (UC).

AREAS OF CONTROVERSY

The pathogenesis is unclear, and competing theories exist surrounding toxic bile acids, enhanced homing of particular T cells from the gut to the liver and increased passage of toxins to the liver through a permeable bowel wall. It is unclear whether the higher rate of colonic cancer in PSC/UC occurs in PSC/Crohn's disease. Ursodeoxycholic acid therapy reduces liver enzymes but has not been shown to improve survival. It may reduce the prevalence of bowel cancer.

GROWING POINTS

Recent genetic studies have revealed new risk loci, pointing to the importance of the immune system and its interaction with the biome.

AREAS TIMELY FOR DEVELOPING RESEARCH

On the basis of the genetic studies discussed earlier, novel agents are being developed and trialled in the treatment of PSC.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

CCR9 antagonism: potential in the treatment of Inflammatory Bowel Disease

Inflammatory Bowel Disease (IBD), mainly comprising Crohn’s disease (CD) and ulcerative colitis (UC), is a chronic condition that primarily affects the intestine and is characterized by leukocytic infiltration. Blocking the migration of leukocytes from the circulation is therefore a reasonable therapeutic goal. Recent clinical trials using this approach have shown promise, with the monoclonal antibody to α₄β₇ integrin, vedolizumab, and previously with the monoclonal antibody to the α₄ subunit, natalizumab. Directly targeting the subset of α₄β₇ expressing cells that co-express CC chemokine receptor 9 (CCR9), using the orally administered antagonist, CCX282-B, also known as vercirnon, has also been evaluated in Phase II and III trials that have produced mixed results. Although CCX282-B showed efficacy in inducing response in active CD in early studies, this was not confirmed in a Phase III study. CCX282-B was also more effective than placebo in maintaining remission, and this result has yet to be confirmed in Phase III. The efficacy of blocking CCR9 in UC, where vedolizumab was effective, has not been tested. The prospect of targeting CCR9 in IBD remains attractive. Much of the local accumulation of inflammatory cells in the intestine arises from migration rather than local proliferation and genetic and pharmacological targeting of CCR9 or its ligand in preclinical models that mimic UC and CD ameliorate inflammation in some cases. Furthermore, binding of chemokine ligands to receptor is a critical step in activating integrin binding, so there is a potential for synergistic action between integrin and chemokine antagonists. CCR9 is expressed on a smaller proportion of circulating cells than α₄β₇ integrin, which may offer greater specificity of effect, particularly in long term use. Furthermore, while α₄β₇ is widely expressed on T and B cell subsets, CCR9 is mainly expressed on effector memory Th1 cells. Indications for the use of intestine-specific integrin and chemokine receptor targeting may also extend beyond IBD, to include, for example, postoperative ileus, and primary sclerosing cholangitis.

Leukocyte homing, fate, and function are controlled by retinoic acid

Although vitamin A was recognized as an "anti-infective vitamin" over 90 years ago, the mechanism of how vitamin A regulates immunity is only beginning to be understood. Early studies which focused on the immune responses in vitamin A-deficient (VAD) animals clearly demonstrated compromised immunity and consequently increased susceptibility to infectious disease. The active form of vitamin A, retinoic acid (RA), has been shown to have a profound impact on the homing and differentiation of leukocytes. Both pharmacological and genetic approaches have been applied to the understanding of how RA regulates the development and differentiation of various immune cell subsets, and how RA influences the development of immunity versus tolerance. These studies clearly show that RA profoundly impacts on cell- and humoral-mediated immunity. In this review, the early findings on the complex relationship between VAD and immunity are discussed as well as vitamin A metabolism and signaling within hematopoietic cells. Particular attention is focused on how RA impacts on T-cell lineage commitment and plasticity in various diseases.

Protective immunity against Chlamydia trachomatis can engage both CD4+ and CD8+ T cells and bridge the respiratory and genital mucosae

Understanding the cellular populations and mechanisms responsible for overcoming immune compartmentalization is valuable for designing vaccination strategies targeting distal mucosae. In this study, we show that the human pathogen Chlamydia trachomatis infects the murine respiratory and genital mucosae and that T cells, but not Abs, elicited through intranasal immunization can protect against a subsequent transcervical challenge. Unlike the genital infection where CD8(+) T cells are primed, yet fail to confer protection, we found that intranasal priming engages both CD4(+) and CD8(+) T cells, allowing for protection against genital infection with C. trachomatis. The protection is largely dependent on IFN-γ secretion by T cells. Moreover, different chemokine receptors are critical for C. trachomatis-specific CD4(+) T cells to home to the lung, rather than the CXCR3- and CCR5-dependent migration observed during genital infection. Overall, this study demonstrates that the cross-mucosa protective immunity against genital C. trachomatis infection following intranasal immunization is not dependent on Ab response but is mediated by not only CD4(+) T cells but also by CD8(+) T cells. This study provides insights for the development of vaccines against mucosal pathogens that threaten reproductive health worldwide.

A role for CCL28-CCR3 in T-cell homing to the human upper airway mucosa

Lymphocyte recruitment to peripheral tissues is fundamental for immune surveillance and homeostasis, but the chemokines and chemokine receptors responsible for tissue-specific homing of T cells to the upper airway mucosa have not been determined. To address this, we analyzed the chemokines expressed in the normal human nasal mucosa and found that CCL28 is preferentially expressed at a high level on the lumenal face of vascular endothelial cells in the mucosa. Analysis of the cognate chemokine receptors revealed that close to 50% of the CD4(+) T cells in the human nasal mucosa expressed the CCL28 receptor CCR3, whereas CCR3 was hardly detectable on T cells in the small intestine and skin. In the circulation, CCR3(+) T cells comprised a small subset that did not express homing receptors to the intestine or skin. Moreover, depletion of CCR3(+)CD4(+) T cells abrogated the proliferative response of human blood CD4(+) T cells against the opportunistic nasopharyngeal pathogen Haemophilus influenzae, indicating that the CCR3(+)CD4(+) T-cell subset in the circulation contains antigen specificities relevant for the upper airways. Together, these findings indicate that CCL28-CCR3 interactions are involved in the homeostatic trafficking of CD4(+) T cells to the upper airways.

Complex adaptive immunity to enteric fevers in humans: lessons learned and the path forward

Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, and S. Paratyphi A and B, causative agents of paratyphoid fever, are major public health threats throughout the world. Although two licensed typhoid vaccines are currently available, they are only moderately protective and immunogenic necessitating the development of novel vaccines. A major obstacle in the development of improved typhoid, as well as paratyphoid vaccines is the lack of known immunological correlates of protection in humans. Considerable progress has been made in recent years in understanding the complex adaptive host responses against S. Typhi. Although the induction of S. Typhi-specific antibodies (including their functional properties) and memory B cells, as well as their cross-reactivity with S. Paratyphi A and S. Paratyphi B has been shown, the role of humoral immunity in protection remains undefined. Cell mediated immunity (CMI) is likely to play a dominant role in protection against enteric fever pathogens. Detailed measurements of CMI performed in volunteers immunized with attenuated strains of S. Typhi have shown, among others, the induction of lymphoproliferation, multifunctional type 1 cytokine production, and CD8(+) cytotoxic T-cell responses. In addition to systemic responses, the local microenvironment of the gut is likely to be of paramount importance in protection from these infections. In this review, we will critically assess current knowledge regarding the role of CMI and humoral immunity following natural S. Typhi and S. Paratyphi infections, experimental challenge, and immunization in humans. We will also address recent advances regarding cross-talk between the host's gut microbiota and immunization with attenuated S. Typhi, mechanisms of systemic immune responses, and the homing potential of S. Typhi-specific B- and T-cells to the gut and other tissues.

Cellular Plasticity of CD4+ T Cells in the Intestine

Barrier sites such as the gastrointestinal tract are in constant contact with the environment, which contains both beneficial and harmful components. The immune system at the epithelia must make the distinction between these components to balance tolerance, protection, and immunopathology. This is achieved via multifaceted immune recognition, highly organized lymphoid structures, and the interaction of many types of immune cells. The adaptive immune response in the gut is orchestrated by CD4⁺ helper T (Th) cells, which are integral to gut immunity. In recent years, it has become apparent that the functional identity of these Th cells is not as fixed as initially thought. Plasticity in differentiated T cell subsets has now been firmly established, in both health and disease. The gut, in particular, utilizes CD4⁺ T cell plasticity to mold CD4⁺ T cell phenotypes to maintain its finely poised balance of tolerance and inflammation and to encourage biodiversity within the enteric microbiome. In this review, we will discuss intestinal helper T cell plasticity and our current understanding of its mechanisms, including our growing knowledge of an evolutionarily ancient symbiosis between microbiota and malleable CD4⁺ T cell effectors.

Abrogation of CC chemokine receptor 9 ameliorates collagen-induced arthritis of mice

INTRODUCTION

Biological drugs are effective in patients with rheumatoid arthritis (RA), but increase severe infections. The CC chemokine receptor (CCR) 9 antagonist was effective for Crohn's disease without critical adverse effects including infections in clinical trials. The present study was carried out to explore the pathogenic roles of chemokine (C-C motif) ligand (CCL) 25 and its receptor, CCR9, in autoimmune arthritis and to study if the CCR9 antagonist could be a new treatment for RA.

METHODS

CCL25 and CCR9 expression was examined with immunohistochemistry and Western blotting. Concentration of interleukin (IL)-6, matrix metalloproteinase (MMP)-3 and tumor necrosis factor (TNF)-α was measured with enzyme-linked immunosorbent assays. Effects of abrogating CCR9 on collagen-induced arthritis (CIA) was evaluated using CCR9-deficient mice or the CCR9 antagonist, CCX8037. Fluorescence labeled-CD11b+ splenocytes from CIA mice were transferred to recipient CIA mice and those infiltrating into the synovial tissues of the recipient mice were counted.

RESULTS

CCL25 and CCR9 proteins were found in the RA synovial tissues. CCR9 was expressed on macrophages, fibroblast-like synoviocytes (FLS) and dendritic cells in the synovial tissues. Stimulation with CCL25 increased IL-6 and MMP-3 production from RA FLS, and IL-6 and TNF-α production from peripheral blood monocytes. CIA was suppressed in CCR9-deficient mice. CCX8037 also inhibited CIA and the migration of transferred CD11b+ splenocytes into the synovial tissues.

CONCLUSIONS

The interaction between CCL25 and CCR9 may play important roles in cell infiltration into the RA synovial tissues and inflammatory mediator production. Blocking CCL25 or CCR9 may represent a novel safe therapy for RA.

Regional specialization within the intestinal immune system

The intestine represents the largest compartment of the immune system. It is continually exposed to antigens and immunomodulatory agents from the diet and the commensal microbiota, and it is the port of entry for many clinically important pathogens. Intestinal immune processes are also increasingly implicated in controlling disease development elsewhere in the body. In this Review, we detail the anatomical and physiological distinctions that are observed in the small and large intestines, and we suggest how these may account for the diversity in the immune apparatus that is seen throughout the intestine. We describe how the distribution of innate, adaptive and innate-like immune cells varies in different segments of the intestine and discuss the environmental factors that may influence this. Finally, we consider the implications of regional immune specialization for inflammatory disease in the intestine.

Evidence for a common mucosal immune system in the pig

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There is evidence that the common mucosal immune system exists in pigs.

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Vaccination at an easily accessible mucosal site may assist in providing protection at other mucosal sites.

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Local and distal mucosal sites should be sampled after vaccinations to define the optimal dose and formulation which promotes the common mucosal immune system in pigs.

The majority of lymphocytes activated at mucosal sites receive instructions to home back to the local mucosa, but a portion also seed distal mucosa sites. By seeding distal sites with antigen-specific effector or memory lymphocytes, the foundation is laid for the animal's mucosal immune system to respond with a secondary response should to this antigen be encountered at this site in the future. The common mucosal immune system has been studied quite extensively in rodent models but less so in large animal models such as the pig. Reasons for this paucity of reported induction of the common mucosal immune system in this species may be that distal mucosal sites were examined but no induction was observed and therefore it was not reported. However, we suspect that the majority of investigators simply did not sample distal mucosal sites and therefore there is little evidence of immune response induction in the literature. It is our hope that more pig immunologists and infectious disease experts who perform mucosal immunizations or inoculations on pigs will sample distal mucosal sites and report their findings, whether results are positive or negative. In this review, we highlight papers that show that immunization/inoculation using one route triggers mucosal immune system induction locally, systemically, and within at least one distal mucosal site. Only by understanding whether immunizations at one site triggers immunity throughout the common mucosal immune system can we rationally develop vaccines for the pig, and through these works we can gather evidence about the mucosal immune system that may be extrapolated to other livestock species or humans.

Intravenous injection of MVA virus targets CD8+ lymphocytes to tumors to control tumor growth upon combinatorial treatment with a TLR9 agonist

Effector T-cell access to tumor tissue is a limiting step for clinical efficacy of antigen-specific T cell-based immunotherapies. Ectopic mouse tumor models, in which a subcutaneously (s.c.) implanted tumor is treated with s.c. or intramuscular therapeutic immunization, may not be optimal for targeting effector T cells to an organ-borne tumor. We used an orthotopic renal carcinoma model to evaluate the impact of injection routes on therapeutic efficacy of a Modified Vaccinia virus Ankara viral vector expressing the human mucin 1 tumor-associated xeno-antigen (MVA-MUC1). We show that intravenous (i.v.) administration of MVA-MUC1 displayed enhanced efficacy when compared with s.c. injection. Therapeutic efficacy of MVA-MUC1 was further enhanced by i.v. injection of a TLR9 agonist. In all cases, infiltration of tumor-bearing kidney by CD8(+) lymphocytes was associated with control of tumor growth. Biodistribution experiments indicate that, following i.v. injection, MVA-encoded antigens are quickly expressed in visceral organs and, in particular, in splenic antigen-presenting cells, compared with those following s.c. injection. This appears to result in a faster generation of MUC1-specific CD8(+) T cells. Lymphocytes infiltrating tumor-bearing kidneys are characterized by an effector memory phenotype and express PD-1 and Tim3 immune checkpoint molecules. Therapeutic efficacy was associated with a modification of the tumor microenvironment toward a Th1-type immune response and recruitment of activated lymphocytes. This study supports the clinical evaluation of MVA-based immunotherapies via the i.v. route.

Mucosal resident memory CD4 T cells in protection and immunopathology

Tissue-resident memory T cells (TRM) comprise a newly defined subset, which comprises a major component of lymphocyte populations in diverse peripheral tissue sites, including mucosal tissues, barrier surfaces, and in other non-lymphoid and lymphoid sites in humans and mice. Many studies have focused on the role of CD8 TRM in protection; however, there is now accumulating evidence that CD4 TRM predominate in tissue sites, and are integral for in situ protective immunity, particularly in mucosal sites. New evidence suggests that mucosal CD4 TRM populations differentiate at tissue sites following the recruitment of effector T cells by local inflammation or infection. The resulting TRM populations are enriched in T-cell specificities associated with the inducing pathogen/antigen. This compartmentalization of memory T cells at specific tissue sites may provide an optimal design for future vaccination strategies. In addition, emerging evidence suggests that CD4 TRM may also play a role in immunoregulation and immunopathology, and therefore, targeting TRM may be a viable therapeutic approach to treat inflammatory diseases in mucosal sites. This review will summarize our current understanding of CD4 TRM in diverse tissues, with an emphasis on their role in protective immunity and the mechanisms by which these populations are established and maintained in diverse mucosal sites.

CCL25/CCR9 interactions are not essential for colitis development but are required for innate immune cell protection from chronic experimental murine colitis

BACKGROUND

The chemokine CCL25, and its receptor CCR9, constitute a unique chemokine/receptor pair, which regulates trafficking of T lymphocytes to the small intestine under physiological conditions and is an attractive target for small bowel Crohn's disease drug development. We have previously shown that CCL25/CCR9 interactions regulate the recovery from acute dextran sulfate sodium-induced colonic inflammation. In this study, we explored whether these interactions also regulate chronic colitis development in 2 independent murine models of experimental colitis.

METHODS

Histological flow cytometry and qPCR analyses were performed to evaluate the role of CL25 and CCR9 in chronic colonic inflammation induced by serial exposures to dextran sulfate sodium salts or by adoptive transfer of CD45RB(hi) CD4(+) T cell into lymphopenic mice devoid of CCL25/CCR9 interactions.

RESULTS

Chronic dextran sulfate sodium exposure results in exacerbated colitis in mice deficient for either CCR9 or CCL25 when compared with wild-type control mice. Although CCR9-deficient T cells traffic to the colon and induce severe colitis similar to wild-type T cells in the CD45RB transfer model, naive wild-type T cells induce more severe disease in recipient animals devoid of CCL25 expression.

CONCLUSIONS

CCL25/CCR9 interactions are required for modulating protection against large intestinal inflammation in 2 models of chronic colitis. These data may have implications for the potential effects of disrupting CCL25/CCR9 interactions in humans in the setting of intestinal disorders including inflammatory bowel disease.

Naïve T cells, unconventional NK and NKT cells, and highly responsive monocyte-derived macrophages characterize human cord blood

This study compares the human immune systems of neonates and adults. Flow cytometric analysis was used to study the cellular phenotypes of cord blood (CB) and adult peripheral blood (APB). Luminex analysis was used to determine the levels of cytokines in cell culture supernatants. Our findings indicate that T cells in CB were mainly naïve and thus less responsive to PMA/ionomycin with the synthesis of cytokines. The percentages of CD3(+)CD4(+)CD25(high) and of CD3(+)CD4(+)CD25(dim) cells expressing chemokine receptors were different between CB and APB. TLR1, TLR6 and TLR9 expressions on NK and NKT cells also differed between CB and APB. CB monocyte-derived macrophages responded better than APB macrophages to TLR ligands with increased secretion of inflammatory cytokines, especially IL-6. The high levels of the inflammatory cytokines in cell culture supernatants of CB were mainly due to higher numbers of responsive macrophages, since dendritic cell numbers were lower in CB than APB.

The chemokine receptor CXCR6 is required for the maintenance of liver memory CD8⁺ T cells specific for infectious pathogens

It is well established that immunization with attenuated malaria sporozoites induces CD8(+) T cells that eliminate parasite-infected hepatocytes. Liver memory CD8(+) T cells induced by immunization with parasites undergo a unique differentiation program and have enhanced expression of CXCR6. Following immunization with malaria parasites, CXCR6-deficient memory CD8(+) T cells recovered from the liver display altered cell-surface expression markers as compared to their wild-type counterparts, but they exhibit normal cytokine secretion and expression of cytotoxic mediators on a per-cell basis. Most importantly, CXCR6-deficient CD8(+) T cells migrate to the liver normally after immunization with Plasmodium sporozoites or vaccinia virus, but a few weeks later their numbers severely decrease in this organ, losing their capacity to inhibit malaria parasite development in the liver. These studies are the first to show that CXCR6 is critical for the development and maintenance of protective memory CD8(+) T cells in the liver.

Induction of Potent and Long-Lived Antibody and Cellular Immune Responses in the Genitorectal Mucosa Could be the Critical Determinant of HIV Vaccine Efficacy

The field of HIV prevention has indeed progressed in leaps and bounds, but with major limitations of the current prevention and treatment options, the world remains desperate for an HIV vaccine. Sadly, this continues to be elusive, because more than 30 years since its discovery there is no licensed HIV vaccine. Research aiming to define immunological biomarkers to accurately predict vaccine efficacy have focused mainly on systemic immune responses, and as such, studies defining correlates of protection in the genitorectal mucosa, the primary target site for HIV entry and seeding are sparse. Clearly, difficulties in sampling and analysis of mucosal specimens, as well as their limited size have been a major deterrent in characterizing the type (mucosal antibodies, cytokines, chemokines, or CTL), threshold (magnitude, depth, and breadth) and viral inhibitory capacity of HIV-1-specific immune responses in the genitorectal mucosa, where they are needed to immediately block HIV acquisition and arrest subsequent virus dissemination. Nevertheless, a few studies document the existence of HIV-specific immune responses in the genitorectal mucosa of HIV-infected aviremic and viremic controllers, as well as in highly exposed persistently seronegative (HEPS) individuals with natural resistance to HIV-1. Some of these responses strongly correlate with protection from HIV acquisition and/or disease progression, thus providing significant clues of the ideal components of an efficacious HIV vaccine. In this study, we provide an overview of the key features of protective immune responses found in HEPS, elite and viremic controllers, and discuss how these can be achieved through mucosal immunization. Inevitably, HIV vaccine development research will have to consider strategies that elicit potent antibody and cellular immune responses within the genitorectal mucosa or induction of systemic immune cells with an inherent potential to home and persist at mucosal sites of HIV entry.

Antitumor effects of a monoclonal antibody to human CCR9 in leukemia cell xenografts

Tumor expression of certain chemokine receptors is associated with resistance to apoptosis, migration, invasiveness and metastasis. Because CCR9 chemokine receptor expression is very restricted in healthy tissue, whereas it is present in tumors of distinct origins including leukemias, melanomas, prostate and ovary carcinomas, it can be considered a suitable candidate for target-directed therapy. Here, we report the generation and characterization of 91R, a mouse anti-human CCR9 IgG2b monoclonal antibody that recognizes an epitope within the CCR9 N-terminal domain. This antibody inhibits the growth of subcutaneous xenografts from human acute T lymphoblastic leukemia MOLT-4 cells in immunodeficient Rag2^−/− mice. Tumor size in 91R-treated mice was reduced by 85% compared with isotype-matched antibody-treated controls. Tumor reduction in 91R-treated mice was concomitant with an increase in the apoptotic cell fraction and tumor necrotic areas, as well as a decrease in the fraction of proliferating cells and in tumor vascularization. In the presence of complement or murine natural killer cells, 91R promoted in vitro lysis of MOLT-4 leukemia cells, indicating that this antibody might eliminate tumor cells via complement- and cell-dependent cytotoxicity. The results show the potential of the 91R monoclonal antibody as a therapeutic agent for treatment of CCR9-expressing tumors.

Tissue-resident memory T cells

Tissues such as the genital tract, skin, and lung act as barriers against invading pathogens. To protect the host, incoming microbes must be quickly and efficiently controlled by the immune system at the portal of entry. Memory is a hallmark of the adaptive immune system, which confers long-term protection and is the basis for efficacious vaccines. While the majority of existing vaccines rely on circulating antibody for protection, struggles to develop antibody-based vaccines against infections such as herpes simplex virus (HSV) and human immunodeficiency virus (HIV) have underscored the need to generate memory T cells for robust antiviral control. The circulating memory T-cell population is generally divided into two subsets: effector memory (TEM ) and central memory (TCM ). These two subsets can be distinguished by their localization, as TCM home to secondary lymphoid organs and TEM circulate through non-lymphoid tissues. More recently, studies have identified a third subset, called tissue-resident memory (TRM ) cells, based on its migratory properties. This subset is found in peripheral tissues that require expression of specific chemoattractants and homing receptors for T-cell recruitment and retention, including barrier sites such as the skin and genital tract. In this review, we categorize different tissues in the body based on patterns of memory T-cell migration and tissue residency. This review also describes the rules for TRM generation and the properties that distinguish them from circulating TEM and TCM cells. Finally, based on the failure of recent T-cell-based vaccines to provide optimal protection, we also discuss the potential role of TRM cells in vaccine design against microbes that invade through the peripheral tissues and highlight new vaccination strategies that take advantage of this newly described memory T-cell subset.

What is left when anti-tumour necrosis factor therapy in inflammatory bowel diseases fails?

The inflammatory bowel diseases (IBDs) are chronic incurable conditions that primarily present in young patients. Being incurable, the IBDs may be part of the patient’s life for many years and these conditions require therapies that will be effective over the long-term. Surgery in Crohn’s disease does not cure the disease with endoscopic recurrent in up to 70% of patients 1 year post resection. This means that, the patient will require many years of medications and the goal of the treating physician is to induce and maintain long-term remission without side effects. The development of the anti-tumour necrosis factor alpha (TNFα) agents has been a magnificent clinical advance in IBD, but they are not always effective, with loss of response overtime and, at times, discontinuation is required secondary to side effects. So what options are available if of the anti-TNFα agents can no longer be used? This review aims to provide other options for the physician, to remind them of the older established medications like azathioprine/6-mercaptopurine and methotrexate, the less established medications like mycophenolate mofetil and tacrolimus as well as newer therapeutic options like the anti-integins, which block the trafficking of leukocytes into the intestinal mucosa. The location of the intestinal inflammation must also be considered, as topical therapeutic agents may also be worthwhile to consider in the long-term management of the more challenging IBD patient. The more options that are available the more likely the patient will be able to have tailored therapy to treat their disease and a better long-term outcome.

Inflammatory pathways of importance for management of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of chronic disorders of the gastrointestinal tract comprising Crohn’s disease (CD) and ulcerative colitis (UC). Their etiologies are unknown, but they are characterised by an imbalanced production of pro-inflammatory mediators, e.g., tumor necrosis factor (TNF)-α, as well as increased recruitment of leukocytes to the site of inflammation. Advantages in understanding the role of the inflammatory pathways in IBD and an inadequate response to conventional therapy in a large portion of patients, has over the last two decades lead to new therapies which includes the TNF inhibitors (TNFi), designed to target and neutralise the effect of TNF-α. TNFi have shown to be efficient in treating moderate to severe CD and UC. However, convenient alternative therapeutics targeting other immune pathways are needed for patients with IBD refractory to conventional therapy including TNFi. Indeed, several therapeutics are currently under development, and have shown success in clinical trials. These include antibodies targeting and neutralising interleukin-12/23, small pharmacologic Janus kinase inhibitors designed to block intracellular signaling of several pro-inflammatory cytokines, antibodies targeting integrins, and small anti-adhesion molecules that block adhesion between leukocytes and the intestinal vascular endothelium, reducing their infiltration into the inflamed mucosa. In this review we have elucidated the major signaling pathways of clinical importance for IBD therapy and highlighted the new promising therapies available. As stated in this paper several new treatment options are under development for the treatment of CD and UC, however, no drug fits all patients. Hence, optimisations of treatment regimens are warranted for the benefit of the patients either through biomarker establishment or other rationales to maximise the effect of the broad range of mode-of-actions of the present and future drugs in IBD.

Human memory T cells: generation, compartmentalization and homeostasis

Memory T cells constitute the most abundant lymphocyte population in the body for the majority of a person's lifetime; however, our understanding of memory T cell generation, function and maintenance mainly derives from mouse studies, which cannot recapitulate the exposure to multiple pathogens that occurs over many decades in humans. In this Review, we discuss studies focused on human memory T cells that reveal key properties of these cells, including subset heterogeneity and diverse tissue residence in multiple mucosal and lymphoid tissue sites. We also review how the function and the adaptability of human memory T cells depend on spatial and temporal compartmentalization.

Diverting T helper cell trafficking through increased plasticity attenuates autoimmune encephalomyelitis

Naive T helper cells differentiate into functionally distinct effector subsets that drive specialized immune responses. Recent studies indicate that some of the effector subsets have plasticity. Here, we used an EAE model and found that Th17 cells deficient in the transcription factor BCL11B upregulated the Th2-associated proteins GATA3 and IL-4 without decreasing RAR-related orphan receptor γ (RORγt), IL-17, and GM-CSF levels. Surprisingly, abnormal IL-4 production affected Th17 cell trafficking, diverting migration from the draining lymph nodes/CNS route to the mesenteric lymph nodes/gut route, which ameliorated EAE without overt colitis. T helper cell rerouting in EAE was dependent on IL-4, which enhanced retinoic acid (RA) production by dendritic cells, which further induced expression of gut-homing receptors CCR9 and α4β7 on Bcl11b-deficient CD4+ T cells. Furthermore, IL-4 treatment or Th2 immunization of wild-type mice with EAE caused no alteration in Th17 cytokines or RORγt, but diverted T helper cell trafficking to the gut, which improved EAE outcome without overt colitis. Our data demonstrate that Th17 cells are permissive to Th2 gene expression without affecting Th17 gene expression. This Th17 plasticity has an impact on trafficking, which is a critical component of the immune response and may represent a possible avenue for treating multiple sclerosis.

Peripheral tissue homing receptor control of naïve, effector, and memory CD8 T cell localization in lymphoid and non-lymphoid tissues

T cell activation induces homing receptors that bind ligands on peripheral tissue vasculature, programing movement to sites of infection and injury. There are three major types of CD8 effector T cells based on homing receptor expression, which arise in distinct lymphoid organs. Recent publications indicate that naïve, effector, and memory T cell migration is more complex than once thought; while many effectors enter peripheral tissues, some re-enter lymph nodes (LN), and contain central memory precursors. LN re-entry can depend on CD62L or peripheral tissue homing receptors. Memory T cells in LN tend to express the same homing receptors as their forebears, but often are CD62Lneg. Homing receptors also control CD8 T cell tumor entry. Tumor vasculature has low levels of many peripheral tissue homing receptor ligands, but portions of it resemble high endothelial venules (HEV), enabling naïve T cell entry, activation, and subsequent effector activity. This vasculature is associated with positive prognoses in humans, suggesting it may sustain ongoing anti-tumor responses. These findings reveal new roles for homing receptors expressed by naïve, effector, and memory CD8 T cells in controlling entry into lymphoid and non-lymphoid tissues.

Expression of the nociceptin/orphanin FQ receptor in the intestinal mucosa of IBS patients

Nociceptin/orphanin FQ (N/OFQ) and the N/OFQ peptide (NOP) receptor play important roles in regulating gastrointestinal function. To assess whether the NOP receptor is implicated in the etiopathogenesis of irritable bowel syndrome (IBS), we measured the levels of NOP receptor mRNA and protein in the jejunal and colonic tissues of healthy subjects and patients with diarrhea-predominant IBS (D-IBS) and constipation-predominant IBS (C-IBS). Mucosal biopsies were obtained from the jejunum and colon of patients diagnosed with D-IBS and C-IBS by the Rome III criteria and from healthy control subjects. The expression of NOP receptor mRNA was measured quantitatively using quantitative PCR (qPCR) and NOP protein expression was assayed immunohistochemically using a rabbit monoclonal antibody to OFQ. NOP receptor mRNA was detected in the jejunum and colon of healthy subjects and was more highly expressed in the jejunum than in the colon. Expression was lower in the jejunum and colon of patients with D-IBS; however, it was similar in patients with C-IBS and healthy subjects. The numbers of OFQ-positive cells in the jejunum and colon were similar among the three groups. The NOP receptor may be involved in the regulation of intestinal movement in healthy individuals. Its involvement in the pathophysiology of IBS may depend on whether the IBS is constipation- or diarrhea-predominant.

Host and microbial factors in regulation of T cells in the intestine

The intestine is divided into specialized tissue areas that provide distinct microenvironments for T cells. Regulation of T-cell responses in the gut has been a major focus of recent research activities in the field. T cells in the intestine are regulated by the interplay between host and microbial factors. In the small intestine, retinoic acid (RA) is a major tissue factor that plays important roles in regulation of immune responses. In the large intestine, the influence of RA diminishes, but that of commensal bacterial products increases. RA, gut microbiota, and inflammatory mediators co-regulate differentiation, distribution, and/or effector functions of T cells. Coordinated regulation of immune responses by these factors promotes well-balanced immunity and immune tolerance. Dysregulation of this process can increase infection and inflammatory diseases.

Thymus-homing dendritic cells in central tolerance

Central tolerance is critical in establishing a peripheral T-cell repertoire purged of functional autoreactive T cells. One of the major requirements for effective central tolerance is the presentation of self and other innocuous antigens (Ags), including food, gut flora, or airway allergens, to developing T cells in the thymus. This seemingly challenging task can be mediated in some cases by ectopic expression of tissue-specific Ags by thymic epithelial cells or by entry of systemic blood-borne Ags into the thymus. More recently, thymic homing peripheral dendritic cells (DCs) have been proposed as cellular transporters of peripheral tissue-specific Ags or foreign innocuous Ags. The aim of this viewpoint is to discuss the three principal thymic DC populations and their trafficking properties in the context of central tolerance. We will first discuss the importance of peripheral DC trafficking to the thymus and then compare and contrast the three DC subsets. We will describe how they were characterized, describe their trafficking to and their microenvironmental positioning in the thymus, and discuss the functional consequence of thymic trafficking and localization on thymic selection events.

Enzyme-linked immunospot assays for direct ex vivo measurement of vaccine-induced human humoral immune responses in blood

The enzyme-linked immunospot (ELISPOT) assay was originally developed to enumerate antigen-specific antibody-secreting cells (ASCs), and has subsequently been adapted for various applications, including the detection cytokine-secreting cells. Owing to its exceptionally high sensitivity, the ELISPOT has proven to be especially useful for detecting discrete populations of active cells (e.g., antigen-specific cells). Because of its versatility, the ELISPOT assay is used for a wide range of applications, including clonal analyses of immune responses after vaccination or after immunotherapy. Here we describe standard protocols for the detection of human ASCs specific to virtually any vaccine antigen after enrichment of circulating plasmablasts. In addition, a protocol is described for the measurement of mucosal ASC responses after prior immunomagnetic enrichment of mucosally derived blood lymphocytes. The protocols described allow rapid (~6-8 h) detection of specific ASCs in small (1-2 ml) samples of blood and can be performed in resource-poor settings.