Repertoire of the alpha beta T-cell receptor in the intestine

Characterisation of T cell receptor repertoires in coeliac disease

AIMS

Characterise T-cell receptor gene (TR) repertoires of small intestinal T cells of patients with newly diagnosed (active) coeliac disease (ACD), refractory CD type I (RCD I) and patients with CD on a gluten-free diet (GFD).

METHODS

Next-generation sequencing of complementarity-determining region 3 (CDR3) of rearranged T cell receptor β (TRB) and γ (TRG) genes was performed using DNA extracted from intraepithelial cell (IEC) and lamina propria cell (LPC) fractions and a small subset of peripheral blood mononuclear cell (PBMC) samples obtained from CD and non-CD (control) patients. Several parameters were assessed, including relative abundance and enrichment.

RESULTS

TRB and TRG repertoires of CD IEC and LPC samples demonstrated lower clonality but higher frequency of rearranged TRs compared with controls. No CD-related differences were detected in the limited number of PBMC samples. Previously published LP gliadin-specific TRB sequences were more frequently detected in LPC samples from patients with CD compared with non-CD controls. TRG repertoires of IECs from both ACD and GFD patients demonstrated increased abundance of certain CDR3 amino acid (AA) motifs compared with controls, which were encoded by multiple nucleotide variants, including one motif that was enriched in duodenal IECs versus the PBMCs of CD patients.

CONCLUSIONS

Small intestinal TRB and TRG repertoires of patients with CD are more diverse than individuals without CD, likely due to mucosal recruitment and accumulation of T cells because of protracted inflammation. Enrichment of the unique TRG CDR3 AA sequence in the mucosa of patients with CD may suggest disease-associated changes in the TCRγδ IE lymphocyte (IEL) landscape.

Gut immune microenvironment and autoimmunity

A variety of immune cells or tissues are present in the gut to form the gut immune microenvironment by interacting with gut microbiota, and to maintain the gut immune homeostasis. Accumulating evidence indicated that gut microbiota dysbiosis might break the homeostasis of the gut immune microenvironment, which was associated with many health problems including autoimmune diseases. Moreover, disturbance of the gut immune microenvironment can also induce extra-intestinal autoimmune disorders through the migration of intestinal pro-inflammatory effector cells from the intestine to peripheral inflamed sites. This review discussed the composition of the gut immune microenvironment and its association with autoimmunity. These findings are expected to provide new insights into the pathogenesis of various autoimmune disorders, as well as novel strategies for the prevention and treatment against related diseases.

Characterization of Bovine Intraepithelial T Lymphocytes in the Gut

Intraepithelial T lymphocytes (T-IELs), which constitute over 50% of the total T lymphocytes in the animal, patrol the mucosal epithelial lining to defend against pathogen invasion while maintaining gut homeostasis. In addition to expressing T cell markers such as CD4 and CD8, T-IELs display T cell receptors (TCR), including either TCRαβ or TCRγδ. Both humans and mice share similar T-IEL subsets: TCRγδ+, TCRαβ+CD8αα+, TCRαβ+CD4+, and TCRαβ+CD8αβ+. Among these subsets, human T-IELs are predominantly TCRαβ+ (over 80%), whereas those in mice are mostly TCRγδ+ (~60%). Of note, the majority of the TCRγδ+ subset expresses CD8αα in both species. Although T-IELs have been extensively studied in humans and mice, their profiles in cattle have not been well examined. Our study is the first to characterize bovine T-IELs using flow cytometry, where we identified several distinct features. The percentage of TCRγδ+ was comparable to that of TCRαβ+ T-IELs (both ~50% of CD3+), and the majority of bovine TCRγδ+ T-IELs did not express CD8 (CD8-) (above 60%). Furthermore, about 20% of TCRαβ+ T-IELs were CD4+CD8αβ+, and the remaining TCRαβ+ T-IELs were evenly distributed between CD4+ and CD8αβ+ (~40% of TCRαβ+ T-IELs each) with no TCRαβ+CD8αα+ identified. Despite these unique properties, bovine T-IELs, similar to those in humans and mice, expressed a high level of CD69, an activation and tissue-retention marker, and a low level of CD62L, a lymphoid adhesion marker. Moreover, bovine T-IELs produced low levels of inflammatory cytokines such as IFNγ and IL17A, and secreted small amounts of the immune regulatory cytokine TGFβ1. Hence, bovine T-IELs' composition largely differs from that of human and mouse, with the dominance of the CD8- population among TCRγδ+ T-IELs, the substantial presence of TCRαβ+CD4+CD8αβ+ cells, and the absence of TCRαβ+CD8αα+ T-IELs. These results provide the groundwork for conducting future studies to examine how bovine T-IELs respond to intestinal pathogens and maintain the integrity of the gut epithelial barrier in animals.

The dephosphorylation of FADD at S191 induces an excessive expansion of TCRαβ+ IELs in the intestinal mucosa

Intestinal intraepithelial lymphocytes (IELs) play a crucial role in host defence against pathogens in the intestinal mucosa. The development of intestinal IELs is distinct from peripheral T lymphocytes and remains elusive. Fas-associated protein with death domain (FADD) is important for T cell development in the thymus. Here we describe a novel function of FADD in the IEL development. FADD (S191A), a mouse FADD mutant at Ser191 to Ala mimicking constitutively unphosphorylated FADD, promoted a rapid expansion of TCRαβ⁺ IELs, not TCRγδ⁺ IELs. Mechanism investigation indicated that the dephosphorylation of FADD was required for cell activation mainly in TCRαβ⁺ CD8⁺ T cells. Consistently, FADD (S191A) as dephosphorylated FADD led to a high NF-κB activation in the TCR-dependent cell expansion. In addition, The FADD (S191A)-induced abnormal IEL populations resulted in the increased incidence and severity of colitis in mice. In summary, FADD signalling is involved in the intestinal IEL development and might be a regulator for intestinal mucosal homeostasis.

Reduced diversity of intestinal T-cell receptor repertoire in patients with Crohn’s disease

Background

The intestinal microenvironment directly determines the human T-cell receptor (TCR) repertoire. Despite its extreme diversity, TCR repertoire analysis may provide a better understanding of the immune system in patients with inflammatory bowel disease.

Methods

To investigate TCR repertoires in the intestinal mucosa, RNA sequencing was performed for inflamed and non-inflamed intestinal mucosa samples obtained from 13 patients with Crohn’s disease (CD) and healthy mucosa from nine non-IBD controls.

Results

The gene expression frequency of the TCR repertoire showed a clear separation between inflamed mucosa of patients with CD and healthy mucosa of non-IBD controls in the hierarchical clustering heatmap. The richness of TCR repertoires measured by the Chao1 index did not show a significant difference among groups, whereas diversity measured by the D50 diversity index was decreased in the inflamed mucosa of CD patients. Rare/small TCR clonotypes occupied a large proportion of TCR repertoires in healthy mucosa of controls, whereas expanded clonotypes were common in inflamed mucosa of patients with CD. Segment usages of TRAV2, TRAV22, TRAV40, TRJ14, TRAJ51, TRBV1, TRBV21.1, and TRBJ1.5 were significantly decreased in CD patients. KEGG enrichment analysis identified the enrichment of several KEGG pathways, including inflammatory bowel disease (p = 0.0012), Th1 and Th2 cell differentiation (p = 0.0011), and intestinal immune network for IgA production (p = 0.0468).

Conclusions

The diversity of the TCR repertoire is reduced in inflamed mucosa of CD patients, which might contribute to intestinal inflammation.

Mechanisms of activation of innate-like intraepithelial T lymphocytes

Intraepithelial T lymphocytes (T-IEL) contain subsets of innate-like T cells that evoke innate and adaptive immune responses to provide rapid protection at epithelial barrier sites. In the intestine, T-IEL express variable T cell antigen receptors (TCR), with unknown antigen specificities. Intriguingly, they also express multiple inhibitory receptors, many of which are normally found on exhausted or antigen-experienced T cells. This pattern suggests that T-IEL are antigen-experienced, yet it is not clear where, and in what context, T-IEL encounter TCR ligands. We review recent evidence indicating TCR antigens for intestinal innate-like T-IEL are found on thymic or intestinal epithelium, driving agonist selection of T-IEL. We explore the contributions of the TCR and various co-stimulatory and co-inhibitory receptors in activating T-IEL effector functions. The balance between inhibitory and activating signals may be key to keeping these highly cytotoxic, rapidly activated cells in check, and key to harnessing their immune surveillance potential.

Intestinal intraepithelial lymphocytes: Maintainers of intestinal immune tolerance and regulators of intestinal immunity

Intestinal immune tolerance is essential for the immune system, as it prevents abnormal immune responses to large quantities of antigens from the intestinal lumen, such as antigens from commensal microorganisms, and avoids self‐injury. Intestinal intraepithelial lymphocytes (IELs), a special group of mucosal T lymphocytes, play a significant role in intestinal immune tolerance. To accomplish this, IELs exhibit a high threshold of activation and low reactivity to most antigens from the intestinal lumen. In particular, CD8αα⁺TCRαβ⁺ IELs, TCRγδ⁺ IELs, and CD4⁺CD8αα⁺ IELs show great potential for maintaining intestinal immune tolerance and regulating intestinal immunity. However, if the intestinal microenvironment becomes abnormal or intestinal tolerance is broken, IELs may be activated abnormally and become pathogenic.

Genomic profiling of intestinal T-cell receptor repertoires in inflammatory bowel disease

Growing evidence shows that inflammatory bowel disease (IBD) results from dysregulation of immune responses to gut microbes. T-cell receptors (TCRs) expressed on the T-cell surface play critical roles in discriminating pathogens from commensal intestinal microorganisms at the front line of the adaptive immune system. The breakdown of this interaction may trigger persistent inflammatory responses to gut bacteria, resulting in IBD. Taking advantage of high-throughput sequencing, we developed an integrated approach to dissect the intestinal TCR repertoires underlying IBD by collecting peripheral blood and inflamed intestine from the same set of 11 IBD cases. The intestinal TCR repertoires show lower clonotype diversity (p < 0.05) and stronger clonal expansion (p < 0.02) than those in the blood. This pattern becomes more profound in TCRs unique to the inflamed tissue compared with shared TCRs. Our approach further identified the increased usage of TRAV12-3 (false discovery rate, FDR < 5%), which biases its choices of J genes towards the reduction of TRAJ37 and TRAJ43 usage (FDR < 20%) in the inflamed intestine. Our genomic profiling suggests that this selective bias of V and J gene usage may lead to a loss of diversity in the intestinal TCR repertoires and result in mucosal inflammation in IBD.

T cell clonal expansions in ileal Crohn's disease are associated with smoking behaviour and postoperative recurrence

T cell clonal expansions are present in the inflamed mucosa of patients with Crohn's disease (CD) and may be implicated in postoperative recurrence after ileocolonic resection.

METHODS

T cell receptor (TCR) analysis was performed in 57 patients included in a prospective multicentre cohort. Endoscopic recurrence was defined by a Rutgeerts score >i0. DNA and mRNA were extracted from biopsies collected from the surgical specimen and endoscopy, and analysed by high throughput sequencing and microarray, respectively.

RESULTS

TCR repertoire in the mucosa of patients with CD displayed diverse clonal expansions. Active smokers at time of surgery had a significantly increased proportion of clonal expansions as compared with non-smokers (25.9%vs17.9%, p=0.02). The percentage of high frequency clones in the surgical specimen was significantly higher in patients with recurrence and correlated with postoperative endoscopic recurrence (area under the curve (AUC) 0.69, 95% CI 0.54 to 0.83). All patients with clonality above 26.8% (18/57) had an endoscopic recurrence. These patients with a high clonality were more frequently smokers than patients with a low clonality (61% vs 23%, p=0.005). The persistence of a similar TCR repertoire at postoperative endoscopy was associated with smoking and disease recurrence. Patients with high clonality showed increased expression of genes associated with CD8 T cells and reduced expression of inflammation-related genes. Expanded clones were found predominantly in the CD8 T cell compartment.

CONCLUSION

Clonal T cell expansions are implicated in postoperative endoscopic recurrence. CD patients with increased proportion of clonal T cell expansions in the ileal mucosa represent a subgroup associated with smoking and where pathogenesis appears as T cell driven.

TRIAL REGISTRATION NUMBER

NCT03458195.

Development, Homeostasis, and Functions of Intestinal Intraepithelial Lymphocytes

The intestine is continuously exposed to commensal microorganisms, food, and environmental agents and also serves as a major portal of entry for many pathogens. A critical defense mechanism against microbial invasion in the intestine is the single layer of epithelial cells that separates the gut lumen from the underlying tissues. The barrier function of the intestinal epithelium is supported by cells and soluble factors of the intestinal immune system. Chief among them are intestinal intraepithelial lymphocytes (iIELs), which are embedded in the intestinal epithelium and represent one of the single largest populations of lymphocytes in the body. Compared with lymphocytes in other parts of the body, iIELs exhibit unique phenotypic, developmental, and functional properties that reflect their key roles in maintaining the intestinal epithelial barrier. In this article, we review the biology of iIELs in supporting normal health and how their dysregulation can contribute to disease.

Altered T cell receptor beta repertoire patterns in pediatric ulcerative colitis

The antigenic specificity of T cells occurs via generation and rearrangement of different gene segments producing a functional T cell receptor (TCR). High-throughput sequencing (HTS) allows in-depth assessment of TCR repertoire patterns. There are limited data concerning whether TCR repertoires are altered in inflammatory bowel disease. We hypothesized that pediatric ulcerative colitis (UC) patients possess unique TCR repertoires, resulting from clonotypical expansions in the gut. Paired blood and rectal samples were collected from nine newly diagnosed treatment-naive pediatric UC patients and four healthy controls. DNA was isolated to determine the TCR-β repertoire by HTS. Significant clonal expansion was demonstrated in UC patients, with inverse correlation between clinical disease severity and repertoire diversity in the gut. Using different repertoire variables in rectal biopsies, a clear segregation was observed between patients with severe UC, those with mild-moderate disease and healthy controls. Moreover, the overlap between autologous blood-rectal samples in UC patients was significantly higher compared with overlap among controls. Finally, we identified several clonotypes that were shared in either all or the majority of UC patients in the colon. Clonal expansion of TCR-β-expressing T cells among UC patients correlates with disease severity and highlights their involvement in mediating intestinal inflammation.

A Single-Tube, EuroClonality-Inspired, TRG Clonality Multiplex PCR Aids Management of Patients with Enteropathic Diseases, including from Formaldehyde-Fixed, Paraffin-Embedded Tissues

Celiac disease is a chronic inflammation of the small intestine with villous atrophy that can become refractory to a gluten-free diet. Two categories of refractory celiac disease can be distinguished by the phenotype of intraepithelial lymphocytes and the status of TRG genes. Their distinction is important because 30% to 50% of type II but only 0% to 14% of type I evolve to an aggressive enteropathy-associated T-cell lymphoma and therefore require intensive treatment. Currently, differential diagnosis integrates immunohistochemistry, immunophenotyping, and TRG clonality analyses, but each has limitations. A single-tube multiplex TRG PCR (ECN) was prospectively compared to an in-house two-tube TRG PCR (N2T) in 73 samples, including 67 cryopreserved intestine tissues. Thirteen formalin-fixed, paraffin-embedded (FFPE) samples were also analyzed retrospectively. The ECN PCR had comparable efficiency to detect major clonal rearrangements in highly infiltrated tissues from T-cell lymphoproliferative disorders and type II refractory celiac disease and to detect the persistence of minor clones in type II refractory celiac disease follow-up samples. The ECN PCR abolished the risk of amplification of false-positive weak clonal rearrangements in cryopreserved specimens and allowed improved detection of clonal rearrangements in DNA from FFPE samples. The ECN PCR allows robust assessment of cryopreserved and FFPE digestive tissues at diagnosis and follow-up of enteropathies with villous atrophy, thus guiding therapeutic management.

Profoundly Expanded T-cell Clones in the Inflamed and Uninflamed Intestine of Patients With Crohn's Disease

BACKGROUND AND AIM

T cells are key players in the chronic intestinal inflammation that characterises Crohn's disease. Here we aim to map the intestinal T-cell receptor [TCR] repertoire in patients with Crohn's disease, using next-generation sequencing technology to examine the clonality of the T-cell compartment in relation to mucosal inflammation and response to therapy.

METHODS

Biopsies were taken from endoscopically inflamed and uninflamed ileum and colon of 19 patients with Crohn's disease. From this cohort, additional biopsies were taken after 8 weeks of remission induction therapy from eight responders and eight non-responders. Control biopsies from 11 patients without inflammatory bowel disease [IBD] were included. The TCRβ repertoire was analysed by next-generation sequencing of biopsy RNA.

RESULTS

Both in Crohn's disease patients and in non-IBD controls, a broad intestinal T-cell repertoire was found, with a considerable part consisting of expanded clones. Clones in Crohn's disease were more expanded [p = 0.008], with the largest clones representing up to as much as 58% of the total repertoire. There was a substantial overlap of the repertoire between inflamed and uninflamed tissue and between ileum and colon. Following therapy, responders showed larger changes in the T-cell repertoire than non-responders, although a considerable part of the repertoire remained unchanged in both groups.

CONCLUSIONS

The intestinal T-cell repertoire distribution in Crohn's disease is different from that in the normal gut, containing profoundly expanded T-cell clones that take up a large part of the repertoire. The T-cell repertoire is fairly stable regardless of endoscopic mucosal inflammation or response to therapy.

Tissue adaptation: Implications for gut immunity and tolerance

Faria et al. discuss the concept that immune cells undergo specialized adaptation to tissue-specific conditions and its potential implications for tolerance and immunity.

Tissue adaptation is an intrinsic component of immune cell development, influencing both resistance to pathogens and tolerance. Chronically stimulated surfaces of the body, in particular the gut mucosa, are the major sites where immune cells traffic and reside. Their adaptation to these environments requires constant discrimination between natural stimulation coming from harmless microbiota and food, and pathogens that need to be cleared. This review will focus on the adaptation of lymphocytes to the gut mucosa, a highly specialized environment that can help us understand the plasticity of leukocytes arriving at various tissue sites and how tissue-related factors operate to shape immune cell fate and function.

How colonization by microbiota in early life shapes the immune system

Microbial colonization of mucosal tissues during infancy plays an instrumental role in the development and education of the host mammalian immune system. These early-life events can have long-standing consequences: facilitating tolerance to environmental exposures or contributing to the development of disease in later life, including inflammatory bowel disease, allergy, and asthma. Recent studies have begun to define a critical period during early development in which disruption of optimal host-commensal interactions can lead to persistent and in some cases irreversible defects in the development and training of specific immune subsets. Here, we discuss the role of early-life education of the immune system during this "window of opportunity," when microbial colonization has a potentially critical impact on human health and disease.

The use of BLT humanized mice to investigate the immune reconstitution of the gastrointestinal tract

The gastrointestinal (GI) track represents an important battlefield where pathogens first try to gain entry into a host. It is also a universe where highly diverse and ever changing inhabitants co-exist in an exceptional equilibrium without parallel in any other organ system of the body. The gut as an organ has its own well-developed and fully functional immune organization that is similar and yet different in many important ways to the rest of the immune system. Both a compromised and an overactive immune system in the gut can have dire and severe consequences to human health. It has therefore been of great interest to develop animal models that recapitulate key aspects of the human condition to better understand the interplay of the host immune system with its friends and its foes. However, reconstitution of the GI tract in humanized mice has been difficult and highly variable in different systems. A better molecular understanding of the development of the gut immune system in mice has provided critical cues that have been recently used to develop novel humanized mouse models that fully recapitulate the genesis and key functions of the gut immune system of humans. Of particular interest is the presence of human gut-associated lymphoid tissue (GALT) aggregates in the gut of NOD/SCID BLT humanized mice that demonstrate the faithful development of bona fide human plasma cells capable of migrating to the lamina propria and producing human IgA1 and IgA2.

Parallel T-cell cloning and deep sequencing of human MAIT cells reveal stable oligoclonal TCRβ repertoire

Mucosal-associated invariant T (MAIT) cells are abundant in humans and recognize conserved bacterial antigens derived from riboflavin precursors, presented by the non-polymorphic MHC class I-like molecule MR1. Here we show that human MAIT cells are remarkably oligoclonal in both the blood and liver, display high inter-individual homology and exhibit a restricted length CDR3β domain of the TCRVβ chain. We extend this analysis to a second sub-population of MAIT cells expressing a semi-invariant TCR conserved between individuals. Similar to 'conventional' MAIT cells, these lymphocytes react to riboflavin-synthesizing microbes in an MR1-restricted manner and infiltrate solid tissues. Both MAIT cell types release Th0, Th1 and Th2 cytokines, and sCD40L in response to bacterial infection, show cytotoxic capacity against infected cells and promote killing of intracellular bacteria, thus suggesting important protective and immunoregulatory functions of these lymphocytes.

Oligoclonal expansions of mucosal T cells in Crohn's disease predominate in NKG2D-expressing CD4 T cells

Crohn's disease (CD) is an inflammatory pathology of the mucosal intestine that results from uncontrolled immune response towards commensal microbes. Clonal expansions of T cells have been found in patients with CD suggesting an antigen-specific stimulation of pathogenic T cells. Here we show, using T-cell receptor repertoire analysis by real-time PCR, that oligoclonal expansions are found in both CD8+ and CD4+ T cells in the blood and intestinal mucosa of CD patients. The majority of CD4+ T-cell-expanded clones are CD4+NKG2D+ T cells. These clonal expansions were found in both inflamed and neighboring healthy tissue and were persisting during the course of the disease. The presence of these CD4+NKG2D+ T-cell clones at the macroscopically normal edge of the surgical resection might be predictive of inflammation relapse post surgery.

The ARNT-STAT3 axis regulates the differentiation of intestinal intraepithelial TCRαβ⁺CD8αα⁺ cells

Intestinal intraepithelial T cells contribute to the regulation of inflammatory responses in the intestine; however, the molecular basis for their development and maintenance is unknown. The aryl hydrocarbon receptor complexes with the aryl hydrocarbon receptor nuclear translocator (ARNT) and senses environmental factors, including gut microbiota. Here, we identify ARNT as a critical regulator of the differentiation of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells. Mice deficient in either ARNT or aryl hydrocarbon receptor show a greater than- eight-fold reduction in the number of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells. The number of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells is increased by treatment with an aryl hydrocarbon receptor agonist in germ-free mice and is decreased by antibiotic treatment. The Arnt-deficient precursors of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells express low amounts of STAT3 and fail to differentiate towards the TCRαβ(+)CD8αα(+) cell fate after IL-15 stimulation, a deficiency that is overcome by overexpression of Stat3. These data demonstrate that the ARNT-STAT3 axis is a critical regulator of TCRαβ(+)CD8αα(+) intestinal intraepithelial T-cell development and differentiation.

IL-2 receptor γ-chain molecule is critical for intestinal T-cell reconstitution in humanized mice

Intestinal immune cells are important in host defense, yet the determinants for human lymphoid homeostasis in the intestines are poorly understood. In contrast, lymphoid homeostasis has been studied extensively in mice, where the requirement for a functional common γ-chain molecule has been established. We hypothesized that humanized mice could offer insights into human intestinal lymphoid homeostasis if generated in a strain with an intact mouse common γ-chain molecule. To address this hypothesis, we used three mouse strains (non-obese diabetic (NOD)/severe-combined immunodeficient (SCID) (N/S); NOD/SCID γ-chain(-/-) (NSG); and Rag2(-/-) γ-chain(-/-) (DKO)) and two humanization techniques (bone marrow liver thymus (BLT) and human CD34(+) cell bone marrow transplant of newborn mice (hu)) to generate four common types of humanized mice: N/S-BLT, NSG-BLT, NSG-hu, and DKO-hu mice. The highest levels of intestinal human T cells throughout the small and large intestines were observed in N/S-BLT mice, which have an intact common γ-chain molecule. Furthermore, the small intestine lamina propria T-cell populations of N/S-BLT mice exhibit a human intestine-specific surface phenotype. Thus, the extensive intestinal immune reconstitution of N/S-BLT mice was both quantitatively and qualitatively better when compared with the other models tested such that N/S-BLT mice are well suited for the analysis of human intestinal lymphocyte trafficking and human-specific diseases affecting the intestines.

Intraepithelial lymphocytes in celiac disease immunopathology

Celiac disease is a T cell-mediated immune disorder induced by dietary gluten that is characterized by the development of an inflammatory anti-gluten CD4 T cell response, anti-gluten antibodies, and autoantibodies against tissue transglutaminase 2 and the activation of intraepithelial lymphocytes (IELs) leading to the destruction of the intestinal epithelium. Intraepithelial lymphocytes represent a heterogeneous population of T cells composed mainly of cytotoxic CD8 T cells residing within the epithelial layer, whose main role is to maintain the integrity of the epithelium by eliminating infected cells and promoting epithelial repair. Dysregulated activation of IELs is a hallmark of CD and is critically involved in epithelial cell destruction and the subsequent development of villous atrophy. In this review, we compare and contrast the phenotype and function of human and mouse small intestinal IELs under physiological conditions. Furthermore, we discuss how conditions of epithelial distress associated with overexpression of IL-15 and non-classical MHC class I molecules induce cytotoxic IELs to become licensed killer cells that upregulate activating NKG2D and CD94/NKG2C natural killer receptors, acquiring lymphokine killer activity. Pathways leading to dysregulated IEL activation could eventually be targeted to prevent villous atrophy and treat patients who respond poorly to gluten-free diet.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

Mucosal T cells in gut homeostasis and inflammation

The antigen-rich environment of the gut interacts with a highly integrated and specialized mucosal immune system that has the challenging task of preventing invasion and the systemic spread of microbes, while avoiding excessive or unnecessary immune responses to innocuous antigens. Disruption of the mucosal barrier and/or defects in gut immune regulatory networks may lead to chronic intestinal inflammation as seen in inflammatory bowel disease. The T-cell populations of the intestine play a critical role in controlling intestinal homeostasis, and their unique phenotypes and diversities reflect the sophisticated mechanisms that have evolved to maintain the delicate balance between immune activation and tolerance at mucosal sites. In this article, we will discuss the specialized properties of mucosal T cells in the context of immune homeostasis and inflammation.

Regional and global changes in TCRalphabeta T cell repertoires in the gut are dependent upon the complexity of the enteric microflora

The repertoire of gut associated T cells is shaped by exposure to microbes, including the natural enteric microflora. Previous studies compared the repertoire of gut associated T cell populations in germ free (GF) and conventional mammals often focussing on intra-epithelial lymphocyte compartments. Using GF, conventional and monocolonised (gnotobiotic) chickens and chicken TCRbeta-repertoire analysis techniques, we determined the influence of microbial status on global and regional enteric TCRbeta repertoires. The gut of conventionally reared chickens exhibited non-Gaussian distributions of CDR3-lengths with some shared over-represented peaks in neighbouring gut segments. Sequence analysis revealed local clonal over-representation. Germ-free chickens exhibited a polyclonal, non-selected population of T cells in the spleen and in the gut. In contrast, gnotobiotic chickens exhibited a biased repertoire with shared clones evident throughout the gut. These data indicate the dramatic influence of enteric microflora complexity on the profile of TCRbeta repertoire in the gut at local and global levels.

Enteral versus parenteral nutrition: effect on intestinal barrier function

Total parenteral nutrition (TPN), or the complete absence of enteral nutrients, is commonly used in a clinical setting. However, a major consequence of TPN administration is the development of mucosal atrophy and a loss of epithelial barrier function (EBF); and this loss may lead to an increase in clinical infections and septicemia. Our laboratory has investigated the mechanism of this TPN-associated loss of EBF using a mouse model. We have demonstrated that the mucosal lymphoid population significantly changes with TPN, and leads to a rise in interferon gamma (IFN-gamma) and decline in interleukin-10 (IL-10) expression-both of which contribute to the loss of EBF. Associated with these cytokine changes is a dramatic decline in the expression of tight junction and adherens junction proteins. This article discusses the potential mechanisms responsible for these changes, and potential strategies to alleviate this loss in EBF.

A clonotype nomenclature for T cell receptors

T cell receptor (TCR) nucleotide sequences are often generated during analyses of T cell responses to pathogens or autoantigens. The most important region of the TCR is the third complementarity-determining region (CDR3) whose nucleotide sequence is unique to each T cell clone. The CDR3 interacts with the peptide and thus is important for recognizing pathogen or autoantigen epitopes. While conventions exist for identifying the various TCR chains, there is a lack of a concise nomenclature that would identify both the amino acid translation and nucleotide sequence of the CDR3. This deficiency makes the comparison of published TCR genetic and proteomic information difficult. To enhance information sharing among different databases and to facilitate computational assessment of clonotypic T cell repertoires, we propose a clonotype nomenclature. The rules for generating a clonotype identifier are simple and easy to follow, and have a built-in error-checking system. The identifier includes the V and J region, the CDR3 length as well as its human or mouse origin. The framework of this naming system could also be expanded to the B cell receptor.

MSI-H colorectal cancers preferentially retain and expand intraepithelial lymphocytes rather than peripherally derived CD8+ T cells

The healthy colorectal mucosa contains many resident intraepithelial lymphocytes (IELs) consisting of partially activated yet hyporesponsive CD8(+) T cells. A predominant feature of colorectal cancers (CRCs) characterized by high levels of microsatellite instability (MSI-H) is heavy infiltration by an intraepithelial population of tumor infiltrating lymphocytes (iTILs). While it has been assumed that these iTILs originate from tumor infiltration by peripheral CD8(+) effector T cells, their origin remains unknown. In light of the phenotypic and functional differences exhibited by IELs and peripheral T cells, elucidation of the precursor population of iTILs in MSI-H CRCs could clarify the role played by these lymphocytes in tumor progression. The aim of the present study was to investigate whether MSI-H CRCs interact differently with IEL- versus peripherally-derived CD8(+) T cells. Using a Transwell assay system to mimic basolateral infiltration of tumor cells by lymphocytes, T cell migration, retention, proliferation and phenotypic alterations were investigated. Results indicate that MSI-H CRCs preferentially retain and expand IEL-derived cells to a greater degree than their microsatellite stable (MSS) counterparts. While MSI-H CRCs also retained more peripherally derived T cells, this number was considerably less than that from the IEL population. While interaction of IELs with either CRC type led to baseline lymphocyte activation, MSS CRCs induced upregulation of additional activation markers on retained IELs compared to MSI-H CRCs. These results suggest that the abundant iTILs present in MSI-H CRCs result from expansion of the preexisting mucosal IEL population and imply a limited prognostic role for iTILs in MSI-H CRC.

Research progress in genetic animal models of inflammatory bowel disease

In inflammatory bowel disease (IBD), experimental models, especially genetic animal models, are known as important tools for detecting potential therapeutic agents and investigating the mechanisms of pathogenesis. This review is intended to cover recent advances in genetic IBD model applications. The models have been classified into two main categories based on the methods of induction: gene knockout (KO) and transgenic.

Protein kinase C theta plays a fundamental role in different types of chronic colitis

BACKGROUND & AIMS

Dysregulated host/microbial interactions induce the development of colitis by activating deleterious acquired immune responses. Activation of CD4(+) T cells is mainly induced through signaling machinery associated with immunologic synapse (IS). A key molecule associated with the IS is protein kinase C (PKC) theta. However, the role of PKCtheta in the pathogenesis of colitis has not fully been defined.

METHODS

The role of PKCtheta for the acquired-immune responses involved in the development of different types of colitis (CD45RB model, T-cell receptor [TCR] alpha knockout [KO] mice and interleukin [IL]-2KO mice) was examined by generating double KO mice and by utilizing cell transfer approaches.

RESULTS

Adoptive transfer of PKCtheta-deficient naïve CD4(+) T cells failed to induce T helper cell (Th) 1-mediated colitis in the immune-deficient host (CD45RB model). Development of Th2-mediated colitis in TCRalphaKO mice was also inhibited by the absence of PKCtheta. In IL-2KO mice, which develop colitis because of dysregulated T-cell homeostasis, deficiency of PKCtheta in CD4(+) T cells failed to induce the development of severe colitis. Interestingly, absence of PKCtheta led to a remarkable decrease in the proliferation, but not apoptosis, of colonic memory CD4(+) T cells. This impaired proliferation resulted in a marked decrease in the colonic CD4(+) T cells that are capable of producing IL-17. In addition, deficiency of PKCtheta inhibited the production of Th2 cytokines by colonic CD4(+) T cells.

CONCLUSIONS

PKCtheta serves as a common and fundamental signaling molecule in the development of different types of colitis and may represent an attractive target for treating inflammatory bowel disease.

Decline in intestinal mucosal IL-10 expression and decreased intestinal barrier function in a mouse model of total parenteral nutrition

Loss of intestinal epithelial barrier function (EBF) is a major problem associated with total parenteral nutrition (TPN) administration. We have previously identified intestinal intraepithelial lymphocyte (IEL)-derived interferon-gamma (IFN-gamma) as a contributing factor to this barrier loss. The objective was to determine whether other IEL-derived cytokines may also contribute to intestinal epithelial barrier breakdown. C57BL6J male mice received TPN or enteral nutrition (control) for 7 days. IEL-derived interleukin-10 (IL-10) was then measured. A significant decline in IEL-derived IL-10 expression was seen with TPN administration, a cytokine that has been shown in vitro to maintain tight junction integrity. We hypothesized that this change in IEL-derived IL-10 expression could contribute to TPN-associated barrier loss. An additional group of mice was given exogenous recombinant IL-10. Ussing chamber experiments showed that EBF markedly declined in the TPN group. TPN resulted in a significant decrease of IEL-derived IL-10 expression. The expression of several tight junction molecules also decreased with TPN administration. Exogenous IL-10 administration in TPN mice significantly attenuated the TPN-associated decline in zonula occludens (ZO)-1, E-cadherin, and occludin expression, as well as a loss of intestinal barrier function. TPN administration led to a marked decline in IEL-derived IL-10 expression. This decline was coincident with a loss of intestinal EBF. As the decline was partially attenuated with the administration of exogenous IL-10, our findings suggest that loss of IL-10 may be a contributing mechanism to TPN-associated epithelial barrier loss.