Differences in intraepithelial lymphocytes in the proximal, middle, distal parts of small intestine, cecum, and colon of mice

TCRαβ+ CD4-/CD8- "double negative" T cells in health and disease-implications for the kidney

Double negative (DN) T cells, one of the least studied T lymphocyte subgroups, express T cell receptor αβ but lack CD4 and CD8 coreceptors. DN T cells are found in multiple organs including kidney, lung, heart, gastrointestinal tract, liver, genital tract, and central nervous system. DN T cells suppress inflammatory responses in different disease models including experimental acute kidney injury, and significant evidence supports an important role in the pathogenesis of systemic lupus erythematosus. However, little is known about these cells in other kidney diseases. Therefore, it is important to better understand different functions of DN T cells and their signaling pathways as promising therapeutic targets, particularly with the increasing application of T cell-directed therapy in humans. In this review, we aim to summarize studies performed on DN T cells in normal and diseased organs in the setting of different disease models with a focus on kidney.

Zebrafish harbor diverse intestinal macrophage populations including a subset intimately associated with enteric neural processes

Intestinal macrophages are essential for gut health but remain understudied outside of human and mouse systems. Here, we establish zebrafish as a powerful model that provides superior imaging capabilities for whole-gut analysis along all dimensions (anterior-posterior and center-outer axes) for dissecting macrophage biology in gastrointestinal health and disease. We utilized high-resolution imaging to show that the zebrafish gut contains bona fide muscularis and mucosal macrophages, as well as surprisingly large subsets intimately associated with enteric neural processes. Interestingly, most muscularis macrophages span multiple gut layers in stark contrast to their mammalian counterparts typically restricted to a single layer. Using macrophage-deficient irf8 zebrafish, we found a depletion of muscularis but not mucosal macrophages, and that they may be dispensable for gross intestinal transit in adults but not during development. These characterizations provide first insights into intestinal macrophages and their association with the enteric nervous system from development to adulthood in teleosts.

Oral immunization induces a novel CXCR6+ β7+ intraepithelial lymphocyte subset predominating in the small intestine

Intestinal T cells form a central part of the front-line defence against foreign organisms and need to be situated in the mucosa where infection occurs. It is well accepted that immunization by a mucosal route favours localization of antigen-specific effector T cells in the mucosal epithelium, while systemic immunization does not. The aim of the study is to determine how homing receptors are specifically involved in retaining effector T cells in the small intestine after oral immunization. We here demonstrate that the chemokine receptor CXCR6, integrins β7 and CD29 contribute differentially to the epithelial retention phenotype of CD8⁺ T cells in the small intestine of mice. CD8⁺ intraepithelial lymphocytes (IELs) of unvaccinated mice are predominantly β7 single positives, and subcutaneous immunization-induced antigen-specific CD8⁺ effector IELs are mainly composed of CXCR6⁺ , CD29⁺ and CXCR6⁺ CD29⁺ cells. Strikingly, the majority of oral immunization-induced antigen-specific CD8⁺ effector IELs exhibit a distinct, tissue-specific CXCR6⁺ β7⁺ double-positive phenotype, cytotoxic potential and enhanced intraepithelial localization. Transfer of antigen-specific CD8⁺ T cells preactivated with certain immuno-stimuli (such as monophosphoryl lipid A) results in increased accumulation of donor IELs with the CXCR6⁺ β7⁺ phenotype. As β7 exclusively paired with αE on IELs, our results strongly suggest that CXCR6 may cooperate with the heterodimer αEβ7 to preferentially retain intestinally induced effector IELs in the epithelium. The identification of this novel IEL phenotype has significant implications for the development of vaccines and therapeutic strategies to enhance gut immunity.

Inherent Immune Cell Variation Within Colonic Segments Presents Challenges for Clinical Trial Design

BACKGROUND AND AIMS

Intestinal biopsy sampling during IBD trials represents a valuable adjunct strategy for understanding drug responses at the tissue level. Given the length and distinctive embryonic origins of the proximal and distal colon, we investigated whether inherent regional differences of immune cell composition could introduce confounders when sampling different disease stages, or pre/post drug administration. Here, we capitalise on novel mass cytometry technology to perform deep immunophenotyping of distinct healthy colonic segments, using the limited numbers of biopsies that can be harvested from patients.

METHODS

Biopsies [2.8 mm] were collected from the caecum, transverse colon, descending colon, and rectum of normal volunteers. Intestinal leukocytes were isolated, stained with a panel of 37 antibodies, and mass cytometry data acquired.

RESULTS

Site-specific patterns of leukocyte localisation were observed. The proximal colon featured increased CD8+ T cells [particularly resident memory], monocytes, and CD19+ B cells. Conversely, the distal colon and rectum tissues exhibited enrichment for CD4+ T cells and antibody-secreting cells. The transverse colon displayed increased abundance of both γδ T cells and NK cells. Subsets of leukocyte lineages also displayed gradients of expression along the colon length.

CONCLUSIONS

Our results show an inherent regional immune cell variation within colonic segments, indicating that regional mucosal signatures must be considered when assessing disease stages or the prospective effects of trial drugs on leukocyte subsets. Precise protocols for intestinal sampling must be implemented to allow for the proper interpretation of potential differences observed within leukocyte lineages present in the colonic lamina propria.

Sentinels at the frontline: the role of intraepithelial lymphocytes in inflammatory bowel disease

Purpose of review

Intestinal mucosal immunity is tightly regulated to ensure effective host defense against invasive microorganisms while limiting the potential for aberrant damage. In inflammatory bowel disease (IBD), an imbalance between effector and regulatory T cell populations results in an uncontrolled inflammatory response to commensal bacteria. Intraepithelial lymphocytes (IEL) are perfectly positioned within the intestinal epithelium to provide the first line of mucosal defense against luminal microbes or rapidly respond to epithelial injury. This review will highlight how IELs promote protective intestinal immunity and discuss the evidence indicating that altered IEL responses contribute to the pathogenesis of IBD.

Recent findings

Although the role of IELs in mucosal homeostasis has been largely underappreciated, many of the same factors that contribute to the dysregulation of host defense in IBD also adversely affect IELs. For example, IL-23 and the endoplasmic reticulum stress response can enhance IEL lytic activity toward enterocytes. Microbial dysbiosis or defective microbial recognition results in the loss of regulatory IELs, further amplifying these pro-inflammatory effects. Migration of T cells into or within the intraepithelial compartment has a profound effect on their differentiation or effector function demonstrating that IELs are exquisitely sensitive to changes in the local intestinal microenvironment.

Summary

Enhanced mechanistic insight into the regulation of IEL survival, differentiation and effector function may provide useful tools to modulate IEL surveillance or enhance IEL regulatory function. Elucidation of these processes may result in the development of novel therapeutics to reduce intestinal inflammation and reinforce the mucosal barrier in IBD.

Heterogeneity across the murine small and large intestine

The small and large intestine of the gastrointestinal tract (GIT) have evolved to have discrete functions with distinct anatomies and immune cell composition. The importance of these differences is underlined when considering that different pathogens have uniquely adapted to live in each region of the gut. Furthermore, different regions of the GIT are also associated with differences in susceptibility to diseases such as cancer and chronic inflammation. The large and small intestine, given their anatomical and functional differences, should be seen as two separate immunological sites. However, this distinction is often ignored with findings from one area of the GIT being inappropriately extrapolated to the other. Focussing largely on the murine small and large intestine, this review addresses the literature relating to the immunology and biology of the two sites, drawing comparisons between them and clarifying similarities and differences. We also highlight the gaps in our understanding and where further research is needed.

The unique surface molecules on intestinal intraepithelial lymphocytes: from tethering to recognizing

Interspersed among epithelial cells (ECs), intraepithelial lymphocytes (IELs) might be important constituents of the physiological and immunological barriers of the intestinal epithelial layer. IELs are composed of memory-effector T cell subtypes bearing the T cell receptor-γδ (TCRγδ) and TCRαβ. The intimate cell adhesion molecules- and tight junction proteins-mediated biological interactions between IELs and ECs ensure that IELs can reside within the intraepithelial compartment and survey large areas of the villus epithelium. As sentinels in this critical interface, IELs express TCRs that recognize antigenic peptides presented by conventional major histocompatibility complex (MHC) molecules or by non-classical MHC molecules. Moreover, IELs monitor for stressed or damaged ECs to mediate pathological responses and maintain intestinal homeostasis. In this review, we address how IELs reside within the epithelium and exert their sentinel functions.

Double Negative (DN) [CD3⁺CD4⁻CD8⁻] T cells correlate with disease progression during HIV infection

Although double negative T (DNT) cells (CD3⁺CD4⁻CD8⁻) share some characteristics with T regulatory cells, the relationship between DNT cells and disease progression in HIV infection is unclear. In this study, we analyzed the relationship between DNT cells and disease progression during the first 2 years of HIV infection. We found that DNT cell numbers tended to decrease with disease progression. There was a positive correlation between DNT cells and CD4 counts. The DNT cell numbers were significantly lower in the high viral load group compared with the low viral load group. Therefore, we conclude that DNT cells correlated with disease progression in HIV infection. These data provide valuable information for further understanding of the role of DNT cells during HIV infection.

Oral vaccines: directed safe passage to the front line of defense

Oral vaccines are safe and easy to administer and convenient for all ages. They have been successfully developed to protect from many infectious diseases acquired through oral transmission. We recently found in animal models that formulation of oral vaccines in a nanoparticle-releasing microparticle delivery system is a viable approach for selectively inducing large intestinal protective immunity against infections at rectal and genital mucosae. These large-intestine targeted oral vaccines are a potential substitute for the intracolorectal immunization, which has been found to be effective against rectogenital infections but is not feasible for mass vaccination. Moreover, the newly developed delivery system can be modified to selectively target either the small or large intestine for immunization and accordingly revealed a regionalized immune system in the gut. Future applications and research endeavors suggested by the findings are discussed.

IBS, NERD and functional dyspepsia are immuno-neuronal disorders of mucosal cytokine imbalances clinically reversible with high potency sucralfate

Irritable bowel syndrome (IBS), non-erosive reflux disorder (NERD), and functional dyspepsia (FD) are best classified as immuno-neuronal disorders of the mucosa or functional mucosal syndromes (FMS). Each appears to be clinically reversible using high potency sucralfate (HPS). In FMS of the GI tract, postprandial nausea, altered motility, discordant peristalsis, vomiting, diarrhea, and hyperalgesia are the clinical expressions of a mucosal imbalance between pro-inflammatory cytokines of up-regulated intra-epithelial lymphocytes (IELs) and feedback anti-inflammatory cytokines tasked with moderating the antigenic response of IELs. Normal functioning GI tract requires an operative balance between pro-inflammatory and anti-inflammatrory cytokines, a balance governed by locally expressed growth factors. The surface concentration of sucralfate can be enhanced 7-23-fold by suspending it in a select concentration of cations and multi-dentate cationic chelators. Increased surface concentration of sucralfate facilitates novel dose effects which include efficient activation of growth factors, quiescence of gated-nociceptor firing and resultant restoration of normal GI function.

Age-dependent changes in intraepithelial lymphocytes (IELs) of the small intestine, cecum, and colon from young adult to aged mice

We previously reported the regional differences in the IELs present in the proximal (P), middle (M), and distal (D) parts of the small intestine, cecum (Ce), and colon (Co) of mice. In this study, we investigated the age-dependent changes in the regional differences of IELs from young adult to aged mice. In this experiment, 3-, 6-, 12-, 18-, and 24-month-old mice were examined. IELs were separately isolated from 5 parts of the intestines and analyzed by flow cytometry. Regional differences in the number and phenotype of IELs showed the same trends in all age groups. The number of IELs was highest in 6-month-old mice and then gradually decreased with age. As to IEL subsets, age-related changes were not seen except for a few subsets among the age groups. We conclude that age-related decreases in IELs in mouse small intestine may be one of the aging phenomena of the intestinal immune system. Such age-related decreases in IELs may be concerned with the increased liability to intestinal infections in the elderly.