Identical T cell clones are located within the mouse gut epithelium and lamina propia and circulate in the thoracic duct lymph

Myeloid Cell-Derived IL-1 Signaling Damps Neuregulin-1 from Fibroblasts to Suppress Colitis-Induced Early Repair of the Intestinal Epithelium

Neuregulin-1 (Nrg1, gene symbol: Nrg1), a ligand of the ErbB receptor family, promotes intestinal epithelial cell proliferation and repair. However, the dynamics and accurate derivation of Nrg1 expression during colitis remain unclear. By analyzing the public single-cell RNA-sequencing datasets and employing a dextran sulfate sodium (DSS)-induced colitis model, we investigated the cell source of Nrg1 expression and its potential regulator in the process of epithelial healing. Nrg1 was majorly expressed in stem-like fibroblasts arising early in mouse colon after DSS administration, and Nrg1-Erbb3 signaling was identified as a potential mediator of interaction between stem-like fibroblasts and colonic epithelial cells. During the ongoing colitis phase, a significant infiltration of macrophages and neutrophils secreting IL-1β emerged, accompanied by the rise in stem-like fibroblasts that co-expressed Nrg1 and IL-1 receptor 1. By stimulating intestinal or lung fibroblasts with IL-1β in the context of inflammation, we observed a downregulation of Nrg1 expression. Patients with inflammatory bowel disease also exhibited an increase in NRG1+IL1R1+ fibroblasts and an interaction of NRG1-ERBB between IL1R1+ fibroblasts and colonic epithelial cells. This study reveals a novel potential mechanism for mucosal healing after inflammation-induced epithelial injury, in which inflammatory myeloid cell-derived IL-1β suppresses the early regeneration of intestinal tissue by interfering with the secretion of reparative neuregulin-1 by stem-like fibroblasts.

The interaction between intestinal microenvironment and stroke

BACKGROUND

Stroke is not only a major cause of disability but also the third leading cause of death, following heart disease and cancer. It has been established that stroke causes permanent disability in 80% of survivors. However, current treatment options for this patient population are limited. Inflammation and immune response are major features that are well-recognized to occur after a stroke. The gastrointestinal tract hosts complex microbial communities, the largest pool of immune cells, and forms a bidirectional regulation brain-gut axis with the brain. Recent experimental and clinical studies have highlighted the importance of the relationship between the intestinal microenvironment and stroke. Over the years, the influence of the intestine on stroke has emerged as an important and dynamic research direction in biology and medicine.

AIMS

In this review, we describe the structure and function of the intestinal microenvironment and highlight its cross-talk relationship with stroke. In addition, we discuss potential strategies aiming to target the intestinal microenvironment during stroke treatment.

CONCLUSION

The structure and function of the intestinal environment can influence neurological function and cerebral ischemic outcome. Improving the intestinal microenvironment by targeting the gut microbiota may be a new direction in treating stroke.

Human intraepithelial lymphocytes

The location of intraepithelial lymphocytes (IEL) between epithelial cells, their effector memory, cytolytic and inflammatory phenotype positions them to kill infected epithelial cells and protect the intestine against pathogens. Human TCRαβ+CD8αβ+ IEL have the dual capacity to recognize modified self via natural killer (NK) receptors (autoreactivity) as well as foreign antigen via the T cell receptor (TCR), which is accomplished in mouse by two cell subsets, the naturally occurring TCRαβ+CD8αα+ and adaptively induced TCRαβ+CD8αβ+ IEL subsets, respectively. The private/oligoclonal nature of the TCR repertoire of both human and mouse IEL suggests local environmental factors dictate the specificity of IEL responses. The line between sensing of foreign antigens and autoreactivity is blurred for IEL in celiac disease, where recognition of stress ligands by induced activating NK receptors in conjunction with inflammatory signals such as IL-15 can result in low-affinity TCR/non-cognate antigen and NK receptor/stress ligand interactions triggering destruction of intestinal epithelial cells.

Suppression of IL-17F, but not of IL-17A, provides protection against colitis by inducing Treg cells through modification of the intestinal microbiota

The cytokines IL-17A and IL-17F have 50% amino-acid identity and bind the same receptor; however, their functional differences have remained obscure. Here we found that Il17f^-/- mice resisted chemically induced colitis, but Il17a^-/- mice did not, and that Il17f^-/- CD45RB^hiCD4⁺ T cells induced milder colitis in lymphocyte-deficient Rag2^-/- mice, accompanied by an increase in intestinal regulatory T cells (T_reg cells). Clostridium cluster XIVa in colonic microbiota capable of inducing T_reg cells was increased in both Il17f^-/- mice and mice given transfer Il17f^-/- T cells, due to decreased expression of a group of antimicrobial proteins. There was substantial production of IL-17F, but not of IL-17A, not only by naive T cells but also by various colon-resident cells under physiological conditions. Furthermore, antibody to IL-17F suppressed the development of colitis, but antibody to IL-17A did not. These observations suggest that IL-17F is an effective target for the treatment of colitis.

Isolation of human lymphocytes with high yield and viability from the gastrointestinal and female reproductive tract of a humanized DRAG mouse

The mucosal tissues of the gut and female reproductive tract (FRT) are susceptible to pathogen infections including bacteria, viruses, and parasites, and are also the targets for immune disorders such as Crohn's disease, inflammatory bowel disease (IBD), and many types of cancers. However, the role of the mucosal immune cells to control these diseases is largely unknown. The limited availability of human mucosal biopsy tissue and the low number of cells that can be isolated from these tissues hampers the characterization of the phenotype and function of human mucosal immune cell subsets. Therefore, human-immune-system humanized mice are surrogate models to investigate the human mucosal immune cell responses during the course of the disease. The current protocols used to harvest the immune cells from the mucosal tissues, however, result in low recovery of cells with poor viability. We have established a novel protocol, which results in a high yield of human lymphocytes with high viability to overcome this issue. The immune cells obtained from a single DRAG mouse by our protocol were sufficient for conducting functional assays and for flow cytometry analyses including phenotypic, exhaustion, and functional panels.

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.

Amelioration of experimental colitis after short-term therapy with glucocorticoid and its relationship to the induction of different regulatory markers

The clinical benefits of short-term therapy with glucocorticoids (GC) in patients with inflammatory bowel disease (IBD) are widely known. However, the effects of this treatment towards the re-establishment of the regulatory network in IBD are not fully explored. We have evaluated the immunological effects of the abbreviated GC therapy in experimental colitis induced by 3% dextran sulphate sodium in C57BL/6 mice. Treatment with GC improved disease outcome, constrained circulating leucocytes and ameliorated intestinal inflammation. The control of the local inflammatory responses involved a reduction in the expression of interferon-γ and interleukin-1β, associated with augmented mRNA levels of peroxisome proliferator-activated receptors (α and γ) in intestine. Furthermore, there was a reduction of CD4⁺ T cells producing interferon-γ, together with an increased frequency of the putative regulatory population of T cells producing interleukin-10, in spleen. These systemic alterations were accompanied by a decrease in the proliferative potential of splenocytes of mice treated in vivo with GC. Notably, treatment with GC also led to an increase in the frequency of the regulatory markers GITR, CTLA-4, PD-1, CD73 and FoxP3, more prominently in spleen. Taken together, our results pointed to a role of GC in the control of leucocyte responsiveness and re-establishment of a regulatory system, which probably contributed to disease control and the restoration of immune balance. Finally, this is the first time that GC treatment was associated with the modulation of a broad number of regulatory markers in an experimental model of colitis.

Adrenal-Derived Hormones Differentially Modulate Intestinal Immunity in Experimental Colitis

The adrenal glands are able to modulate immune responses through neuroimmunoendocrine interactions and cortisol secretion that could suppress exacerbated inflammation such as in inflammatory bowel disease (IBD). Therefore, here we evaluated the role of these glands in experimental colitis induced by 3% dextran sulfate sodium (DSS) in C57BL/6 mice subjected to adrenalectomy, with or without glucocorticoid (GC) replacement. Mice succumbed to colitis without adrenals with a higher clinical score and augmented systemic levels of IL-6 and lower LPS. Furthermore, adrenalectomy negatively modulated systemic regulatory markers. The absence of adrenals resulted in augmented tolerogenic lamina propria dendritic cells but no compensatory local production of corticosterone and decreased mucosal inflammation associated with increased IFN-γ and FasL in the intestine. To clarify the importance of GC in this scenario, GC replacement in adrenalectomized mice restored different markers to the same degree of that observed in DSS group. Finally, this is the first time that adrenal-derived hormones, especially GC, were associated with the differential local modulation of the gut infiltrate, also pointing to a relationship between adrenalectomy and the modulation of systemic regulatory markers. These findings may elucidate some neuroimmunoendocrine mechanisms that dictate colitis outcome.

CD8αα TCRαβ Intraepithelial Lymphocytes in the Mouse Gut

The epithelium of the mouse small intestine harbors an abundant CD8αα(+)TCRαβ(+) intraepithelial lymphocyte (IEL) population. This unique IEL subset is a self-reactive population that requires exposure to self-agonists for selection in the thymus, similarly to other regulatory T cell populations. After leaving the thymus, these cells directly seed the intestinal epithelium, which provides a unique combination of cellular interactions together with cytokines, nutrients, and antigens that guide the lineage-specific differentiation and function of these IELs. For instance, epithelial cells and nearby immune cells secrete a number of cytokines, including interleukin-15 (IL-15), IL-7, and transforming growth factor-β, resulting in an assortment of cellular responses, including activation of master transcription factors, cell proliferation, and cytokine secretion. Recent advances have also highlighted the importance of diet-derived substances and commensal metabolites, such as the aryl hydrocarbon receptor ligands and vitamin D, in controlling the survival and gene expression of CD8αα(+)TCRαβ(+) IELs. Furthermore, these cells function in the epithelium and require constant communication between cells in the form of cell-to-cell contacts. These interactions tune the antigen sensitivity of the TCR and maintain the quiescence of the CD8αα(+)TCRαβ(+) IELs. Finally, we discuss how these cells might contribute to tolerance and immunopathological responses in the gut. Therefore, an increased understanding of CD8αα(+)TCRαβ(+) IELs in the gut will help us understand how these cells participate in immune regulation and protection.

Inhibition of Dectin-1 Signaling Ameliorates Colitis by Inducing Lactobacillus-Mediated Regulatory T Cell Expansion in the Intestine

Dectin-1, the receptor for β-glucans, protects the host against fungal infection; however, its role in intestinal immunity is incompletely understood. We found that Dectin-1-deficient (Clec7a(-/-)) mice were refractory to both dextran sodium sulfate (DSS)- and CD45RB(high)CD4(+) T cell-induced colitis, and that this resistance was associated with an increase in regulatory T (Treg) cells. The proportion of lactobacilli, especially Lactobacillus murinus, in the commensal microflora was increased in Clec7a(-/-) mouse colons, and accompanied by a decrease in antimicrobial peptides induced by Dectin-1 signaling. L. murinus colonization increased Treg cells in the colon. Oral administration of laminarin, a Dectin-1 antagonist, suppressed the development of DSS-colitis, associated with an increase of L. murinus and Treg cells. Human patients with inflammatory bowel disease were found to have a decreased proportion of closely related Lactobacillus species. These observations suggest that Dectin-1 regulates the homeostasis of intestinal immunity by controlling Treg cell differentiation through modification of microbiota.

Mucosal-associated invariant T cell-rich congenic mouse strain allows functional evaluation

Mucosal-associated invariant T cells (MAITs) have potent antimicrobial activity and are abundant in humans (5%-10% in blood). Despite strong evolutionary conservation of the invariant TCR-α chain and restricting molecule MR1, this population is rare in laboratory mouse strains (≈0.1% in lymphoid organs), and lack of an appropriate mouse model has hampered the study of MAIT biology. Herein, we show that MAITs are 20 times more frequent in clean wild-derived inbred CAST/EiJ mice than in C57BL/6J mice. Increased MAIT frequency was linked to one CAST genetic trait that mapped to the TCR-α locus and led to higher usage of the distal Vα segments, including Vα19. We generated a MAIThi congenic strain that was then crossed to a transgenic Rorcgt-GFP reporter strain. Using this tool, we characterized polyclonal mouse MAITs as memory (CD44+) CD4-CD8lo/neg T cells with tissue-homing properties (CCR6+CCR7-). Similar to human MAITs, mouse MAITs expressed the cytokine receptors IL-7R, IL-18Rα, and IL-12Rβ and the transcription factors promyelocytic leukemia zinc finger (PLZF) and RAR-related orphan receptor γ (RORγt). Mouse MAITs produced Th1/2/17 cytokines upon TCR stimulation and recognized a bacterial compound in an MR1-dependent manner. During experimental urinary tract infection, MAITs migrated to the bladder and decreased bacterial load. Our study demonstrates that the MAIThi congenic strain allows phenotypic and functional characterization of naturally occurring mouse MAITs in health and disease.

The Interaction among Microbiota, Immunity, and Genetic and Dietary Factors Is the Condicio Sine Qua Non Celiac Disease Can Develop

Celiac disease (CD) is an immune-mediated enteropathy, triggered by dietary wheat gluten and similar proteins of barley and rye in genetically susceptible individuals. This is a complex disorder involving both environmental and immune-genetic factors. The major genetic risk factor for CD is determined by HLA-DQ genes. Dysfunction of the innate and adaptive immune systems can conceivably cause impairment of mucosal barrier function and development of localized or systemic inflammatory and autoimmune processes. Exposure to gluten is the main environmental trigger responsible for the signs and symptoms of the disease, but exposure to gluten does not fully explain the manifestation of CD. Thus, both genetic determination and environmental exposure to gluten are necessary for the full manifestation of CD; neither of them is sufficient alone. Epidemiological and clinical data suggest that other environmental factors, including infections, alterations in the intestinal microbiota composition, and early feeding practices, might also play a role in disease development. Thus, this interaction is the condicio sine qua non celiac disease can develop. The breakdown of the interaction among microbiota, innate immunity, and genetic and dietary factors leads to disruption of homeostasis and inflammation; and tissue damage occurs. Focusing attention on this interaction and its breakdown may allow a better understanding of the CD pathogenesis and lead to novel translational avenues for preventing and treating this widespread disease.

MAIT cells are depleted early but retain functional cytokine expression in HIV infection

Mucosal-associated invariant T (MAIT) cells home to mucosal sites and exert antimicrobial activity against bacteria and other microorganisms. HIV infection leads to early depletion of gut T cells and translocation of bacterial products. There are reports that MAIT cells, defined by coexpression of Vα7.2 and CD161, are depleted during HIV infection and residual MAIT cells are functionally impaired. However, one study suggested that MAIT cells might remain after HIV infection but evade detection through CD161 downregulation. Thus, the impact of HIV infection on MAIT cells is unclear. We studied longitudinal blood samples from 31 HIV-infected subjects for MAIT cell numbers, phenotype and function using both standard Vα7.2/CD161 surface markers and an MR1 tetramer. We found that MAIT cells were depleted early during HIV infection, and although there was a concomitant rise in Vα7.2(+)CD161(-) cells, these were MR1 tetramer negative, indicating that these are unlikely to be altered MAIT cells. Antigen-mediated activation of residual MAIT cells showed that they remained functional out to 2 years following HIV infection. Although MAIT cells are depleted in HIV infection, residual and functionally active MAIT cells persist and may still be able to assist in controlling bacterial translocation during HIV infection.

GPR18 is required for a normal CD8αα intestinal intraepithelial lymphocyte compartment

Intraepithelial lymphocytes (IELs) play an important role in maintaining the physiology of the small intestine. The majority of mouse IELs express CD8αα and are either γδ or αβ T cells. Although the development and homing of CD8αα IELs have been studied in some detail, the factors controlling their homeostasis and positioning are incompletely understood. Here we demonstrate that G protein-coupled receptor 18 (GPR18) is abundantly expressed in CD8αα IELs and that mice lacking this orphan receptor have reduced numbers of γδT IELs. Mixed bone marrow chimera experiments reveal a markedly reduced contribution of GPR18-deficient cells to the CD8αα IEL compartment and a reduction in the CD8αβ T cell subset. These defects could be rescued by transduction with a GPR18-expressing retrovirus. The GPR18-deficient γδT IELs that remained in mixed chimeras had elevated Thy1, and there were less granzyme B(+) and Vγ7(+) cells, indicating a greater reduction in effector-type cells. Flow cytometric analysis indicated GPR18 deficiency more strongly affected the CD8αα cells in the intraepithelial compared with the adjacent lamina propria compartment. These findings establish a requirement for GPR18 in CD8αα and CD8αβ IELs, and we suggest the receptor has a role in augmenting the accumulation of CD8 T cells in the intraepithelial versus lamina propria compartment.

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.

Interactions between the intestinal microbiota and innate lymphoid cells

The mammalian intestine must manage to contain 100 trillion intestinal bacteria without inducing inappropriate immune responses to these microorganisms. The effects of the immune system on intestinal microorganisms are numerous and well-characterized, and recent research has determined that the microbiota influences the intestinal immune system as well. In this review, we first discuss the intestinal immune system and its role in containing and maintaining tolerance to commensal organisms. We next introduce a category of immune cells, the innate lymphoid cells, and describe their classification and function in intestinal immunology. Finally, we discuss the effects of the intestinal microbiota on innate lymphoid cells.

Use of gnotobiotic mice to identify and characterize key microbes responsible for the development of the intestinal immune system

Symbiosis between intestinal microbiota and the host animal plays an important role in the homeostasis of host physiology. Since the first production of germ-free rodents in 1945, it has become increasingly clear that the intestinal immune system and the biochemical characteristics of epithelial cells differ greatly between conventional and germ-free rodents. However, questions remain about the types of microbes involved and the precise mechanism by which these microbes affect the host physiology. Here, we review experiments designed to answer these questions with the use of gnotobiotic mice. We have determined suitable biochemical and immunological markers for monitoring microbial effects in these mice. Using these markers, we have found clear differences in epithelial cell glycolipid biosynthesis and intraepithelial lymphocyte dynamics between germ-free and conventional mice. Furthermore, we have identified a key microbe that activates the mucosal immune system in the small intestine. This indigenous bacteria, called segmented filamentous bacteria, is a key symbiont in the host-microbiota interplay, including Th17 cell-inducing activity.

Toxoplasma gondii soluble tachyzoite antigen triggers protective mechanisms against fatal intestinal pathology in oral infection of C57BL/6 mice

Toxoplasma gondii induces a potent IL-12 response early in infection that results in IFN-γ-dependent control of parasite growth. It was previously shown that T. gondii soluble tachyzoite antigen (STAg) injected 48 hr before intraperitoneal infection reduces lipoxin A₄ and 5-lipoxygenase (5-LO)-dependent systemic IL-12 and IFN-γ production as well as hepatic immunopathology. This study investigated the ability of STAg-pretreatment to control the fatal intestinal pathology that develops in C57BL/6 mice orally infected with 100 T. gondii cysts. STAg-pretreatment prolonged the animals’ survival by decreasing tissue parasitism and pathology, mainly in the ilea. Protection was associated with decreases in the systemic IFN-γ levels and IFN-γ and TNF message levels in the ilea and with increased TGF-β production in this tissue, but protection was independent of 5-LO and IL-4. STAg-pretreatment decreased CD4⁺ T cell, NK cell, CD11b⁺ monocyte and CD11b⁺CD11c⁺ dendritic cell numbers in the lamina propria and increased CD8⁺ T cells in the intestinal epithelial compartment. In parallel, decreases were observed in iNOS and IL-17 expression in this organ. These results demonstrate that pretreatment with STAg can induce the recruitment of protective CD8⁺ T cells to the intraepithelial compartment and decrease proinflammatory immune mechanisms that promote intestinal pathology in T. gondii infection.

Origin, trafficking, and intraepithelial fate of gut-tropic T cells

Tropism to the small intestinal epithelium is a general property of unconventional and conventional recent thymic emigrants, but for both cell types only GALT-related cycling thoracic duct lymphocytes are the precursors of cytotoxic intraepithelial lymphocytes.

The small intestine epithelium (SI-Ep) harbors millions of unconventional (γδ and CD4⁻ CD8⁻ NK1.1⁻ TCRαβ) and conventional (CD8αβ and CD4) T cells, designated intraepithelial lymphocytes (IELs). Here, we identified the circulating pool of SI-Ep–tropic T cells and studied their capacity to colonize the SI-Ep under steady-state conditions in SPF mice. Developmentally regulated levels of α4β7 endowed recent thymic emigrants (RTEs) of unconventional types with higher SI-Ep tropism than their conventional homologues. SI-Ep–tropic RTEs, which in all lineages emerged naive, homed to the SI-Ep, but this environment was inadequate to stimulate them to cycle. In contrast, conventional and, unexpectedly, unconventional T cells, particularly Vγ7⁺ (hallmark of γδ IELs), previously stimulated to cycle in the gut-associated lymphoid tissue (GALT), proliferated in the SI-Ep. Cycling unconventional SI-Ep immigrants divided far more efficiently than their conventional homologues, thereby becoming predominant. This difference impacted on acquisition of high Granzyme B content, which required extensive proliferation. In conclusion, SI-Ep–tropic T cells follow a thymus–SI-Ep or a GALT–SI-Ep pathway, the latter generating highly competitive immigrants that are the sole precursors of cytotoxic IELs. These events occur continuously as part of the normal IEL dynamics.

Impact of enzymatic tissue disintegration on the level of surface molecule expression and immune cell function

Immunological characterization of immune cells that reside in specific anatomic compartments often requires their isolation from the respective tissue on the basis of enzymatic tissue disintegration. Applying enzymatic digestion of primary splenocytes, we evaluated the impact of collagenase and dispase, two enzymes that are commonly used for the liberation of immune cells from tissues, on the detectability of 48 immunologically relevant surface molecules that are frequently used for flow cytometric identification, isolation, and characterization of immune cell subsets. Whereas collagenase treatment had only minor effects on surface expression of most molecules tested, dispase treatment considerably affected antibody-mediated detectability of the majority of surface markers in subsequent FACS analyses. This effect was long lasting and, in case of high-dose dispase treatment, evident for the majority of surface molecules even after 24 h of in vitro culture. Of note, high-dose dispase treatment not only affected surface expression of certain molecules but also impaired antigen-specific proliferation of CD4(+) and CD8(+) T cells. Together, our data indicate that enzymatic tissue disintegration can have profound effects on the expression of a variety of cell-surface molecules with direct consequences for phenotypic analysis, FACS- and MACS-based target cell isolation, and immune cell function in cell culture experiments.

Antigen-independent differentiation and maintenance of effector-like resident memory T cells in tissues

Differentiation and maintenance of recirculating effector memory CD8 T cells (T(EM)) depends on prolonged cognate Ag stimulation. Whether similar pathways of differentiation exist for recently identified tissue-resident effector memory T cells (T(RM)), which contribute to rapid local protection upon pathogen re-exposure, is unknown. Memory CD8αβ(+) T cells within small intestine epithelium are well-characterized examples of T(RM), and they maintain a long-lived effector-like phenotype that is highly suggestive of persistent Ag stimulation. This study sought to define the sources and requirements for prolonged Ag stimulation in programming this differentiation state, including local stimulation via cognate or cross-reactive Ags derived from pathogens, microbial flora, or dietary proteins. Contrary to expectations, we found that prolonged cognate Ag stimulation was dispensable for intestinal T(RM) ontogeny. In fact, chronic antigenic stimulation skewed differentiation away from the canonical intestinal T cell phenotype. Resident memory signatures, CD69 and CD103, were expressed in many nonlymphoid tissues including intestine, stomach, kidney, reproductive tract, pancreas, brain, heart, and salivary gland and could be driven by cytokines. Moreover, TGF-β-driven CD103 expression was required for T(RM) maintenance within intestinal epithelium in vivo. Thus, induction and maintenance of long-lived effector-like intestinal T(RM) differed from classic models of T(EM) ontogeny and were programmed through a novel location-dependent pathway that was required for the persistence of local immunological memory.

Luminal CD4⁺ T cells penetrate gut epithelial monolayers and egress from lamina propria to blood circulation

BACKGROUND & AIMS

The egress of memory T cells from peripheral tissues, such as lung and skin, into the draining lymph nodes requires their expression of CC chemokine receptor 7 (CCR7). In the intestine, resident memory T cells in the intestinal lamina propria (LP) do not express CCR7, indicating that they are tissue bound and do not exit the intestine.

METHODS

We developed a cell transfer system, using rectal administration of lymphocytes to C57BL/6 mice. Lymphotoxin α-deficient mice were crossed with RAG-2(-/-) (recombination-activating gene-2) mice to generate lymphotoxin α-deficient × RAG-2(-/-) mice.

RESULTS

Severe combined immunodeficient (SCID) or RAG-2(-/-) mice given rectal administration of splenic CD4(+) T cells from normal mice developed colitis; the cells proliferated not only in the LP but also in spleen. SCID or RAG-2(-/-) mice given rectal administrations of CD4(+) T cells that expressed green fluorescent protein (GFP(+)CD4(+) T cells) localized to the LP within 6 hours but were not found in the spleen until 24 hours after administration. Immunohistochemical and electron microscopic analyses detected CD4(+) T cells in the intraepithelial space just 3 hours after intrarectal administration. However, neither CCR7 deficiency nor the sphingosine-1-phosphate receptor agonist Fingolimod impaired the egress of CD4(+) T cells from LP to systemic circulation.

CONCLUSIONS

CD4(+) T cells not only penetrate from the luminal side of the intestine to the LP but also actively egress from the LP into the circulation. We developed a rectal administration system that might be used to further investigate cell trafficking in intestinal mucosa and to develop enema-based therapeutics for intestinal diseases.

Mycobacterium bovis Bacillus Calmette-Guérin killed by extended freeze-drying reduces colitis in mice

BACKGROUND & AIMS

Mycobacterium bovis Bacillus Calmette-Guérin (BCG), killed by extended freeze-drying (EFD), induces secretion of interleukin-10 and reduces lung inflammation in a mouse model of asthma. We investigated the effects of EFD BCG in mouse models of inflammatory bowel disease.

METHODS

EFD BCG was administered subcutaneously to mice with colitis induced by dextran sodium sulfate (DSS), oxazolone, or adoptive transfer of CD4(+)CD45RB(high)Foxp3(-) T cells from C57Bl/6 Foxp3GFP mice to RAG2(-/-) mice.

RESULTS

EFD BCG, administered either before induction of DSS and oxazolone colitis or after development of acute or chronic DSS-induced colitis, reduced symptom scores, loss of body weight, and inflammation. Although transfer of CD4(+)CD45RB(high)Foxp3(-) cells induced colitis in RAG2(-/-) mice, administration of EFD BCG at the time of the transfer converted Foxp3(-) T cells to Foxp3(+) T cells and the mice did not develop colitis. EFD BCG protected mice from colitis via a mechanism that required expansion of T regulatory cells and production of interleukin-10 and transforming growth factor β. EFD BCG activated the retinoid X receptor (RXR)-α-peroxisome proliferator-activated receptor (PPAR)-γ heterodimer, blocked translocation of nuclear factor κB to the nucleus, and reduced colonic inflammation; it did not increase the number of colon tumors that formed in mice with chronic DSS-induced colitis.

CONCLUSIONS

EFD BCG controls severe colitis in mice by expanding T regulatory cell populations and PPAR-γ and might be developed to treat patients with inflammatory bowel disease.

The light and dark sides of intestinal intraepithelial lymphocytes

The intraepithelial lymphocytes (IELs) that reside within the epithelium of the intestine form one of the main branches of the immune system. As IELs are located at this critical interface between the core of the body and the outside environment, they must balance protective immunity with an ability to safeguard the integrity of the epithelial barrier: failure to do so would compromise homeostasis of the organism. In this Review, we address how the unique development and functions of intestinal IELs allow them to achieve this balance.

Inhibition of phosphoinositide 3-kinase ameliorates dextran sodium sulfate-induced colitis in mice

The critical role of phosphoinositide 3-kinase gamma (PI3Kgamma) in inflammatory cell activation and recruitment makes it an attractive target for immunomodulatory therapy. 5-Quinoxilin-6-methylene-1,3-thiazolidine-2,4-dione (AS605240), a potent PI3Kgamma inhibitor, has been reported to ameliorate chronic inflammatory disorders including rheumatoid arthritis, systemic lupus erythematosus, and atherosclerosis. However, its in vivo effect on intestinal inflammation remains unknown. Here we evaluated the protective and therapeutic potentials of AS605240 in mice with dextran sodium sulfate (DSS)-induced acute and chronic colitis. Our results showed that AS605240 improved survival rate, disease activity index, and histological damage score in mice administered DSS in both preventive and therapeutic studies. AS605240 treatment also significantly inhibited the increase in myeloperoxidase levels, macrophage infiltration, and CD4(+) T-cell number in the colon of DSS-fed mice. The DSS-induced overproduction of colonic proinflammatory cytokines including interleukin (IL)-1beta, tumor necrosis factor-alpha, and interferon-gamma was significantly suppressed in mice undergoing AS605240 therapy, whereas colonic anti-inflammatory cytokines such as IL-4 were up-regulated. The down-regulation of the phospho-Akt level in immunological cells from the inflamed colon tissue and spleen of AS605240-treated mice was detected both by immunohistochemical analysis and Western blotting. These findings demonstrate that AS605240 may represent a promising novel agent for the treatment of inflammatory bowel disease by suppressing leukocyte infiltration as well as by immunoregulating the imbalance between proinflammatory and anti-inflammatory cytokines.

Non-equilibrium and differential function between intraepithelial and lamina propria virus-specific TCRalphabeta(+) CD8alphabeta(+) T cells in the small intestinal mucosa

The gastrointestinal mucosa regularly encounters commensal and pathogenic microbiota. Gut mucosal lymphocytes consist of two phenotypically different populations residing in the intestinal intraepithelial (IEL) compartment and lamina propria (LP). Little is known about compositional and functional differences of antigen-specific T cells from these mucosal compartments after mucosal infection, or the degree of trafficking between them. We here studied the B8R(20-27)-specific CD8 T-cell response in LP and IEL compartments after intrarectal immunization with modified vaccinia virus Ankara (MVA). CD8(+) T cells in the IEL compartment had much lower avidity than in the LP or spleen during acute and memory phases. Surprisingly, the TCR Vbeta-chain distribution of antigen-specific T cells and the length of the CDR3 region of the dominant Vbeta genes showed substantial dissimilarities between IEL and LP antigen-specific CD8alphabeta T cells in individual mice, increasing with time. We show functional and compositional differences between these mucosal compartments during the effector and memory phases of the immune response, indicating limited crosstalk and microenvironmental differences between the IEL, LP, and spleen. The restricted migration of cells from each of these mucosal compartments could partly account for a founder effect we observed in the IEL TCRalphabeta CD8alphabeta epitope-specific repertoire that might impact protective efficacy.

Differential expression of leukocyte functions associated antigen-1 (LFA-1) on peripheral blood mononuclear cells in patients with Crohn's disease

BACKGROUND

The leukocyte function associated antigen-1 (LFA-1) intracellular adhesion molecule-1 pathway is presumed to play a pivotal role in the perpetuation of inflammatory bowel disease. We aimed to elucidate the effect of 2 different therapies on LFA-1 expression in patients with Crohn's disease (CD) and correlate LFA-1 expression with disease activity.

METHODS

In all, 30 patients with active CD were recruited for the present investigation. Eleven patients were treated with infliximab and 19 patients with total parenteral nutrition. The clinical activity and the expression of LFA-1 in peripheral blood mononuclear cells were assessed prior to and 4 weeks after treatment. Clinical activity was determined by measuring the Crohn's Disease Activity Index and LFA-1 expression was measured by mean fluorescence intensity (MFI) under fluorescence-activated cell sorter analysis.

RESULTS

In each treatment group the clinical disease activity index decreased significantly 4 weeks after treatment. In patients treated with infliximab, LFA-1 expression decreased significantly (mean MFI decreased from 1983 to 1487, P < 0.05). However, LFA-1 expression remained unchanged in the total parenteral nutrition group (mean MFI elevated from 1684 to 1902, P > 0.05).

CONCLUSIONS

The mechanism of therapeutic action on CD is different between infliximab and total parenteral nutrition.

Intestinal T cells: facing the mucosal immune dilemma with synergy and diversity

The epithelium of the gastrointestinal tract, which represents the greatest body surface area exposed to the outside environment, is confronted with a plethora of foreign and potentially harmful antigens. Consequently, the immune system of the gut faces the daunting task of distinguishing harmless dietary proteins and commensal bacteria from potentially dangerous pathogens, and of then responding accordingly. Mucosal T cells play a central role in maintaining barrier function and controlling the delicate balance between immune activation and immune tolerance. This review will focus on the unique features of mucosal T cell subsets that reside in the epithelium and lamina propria of the gut.

Uneven colonization of the lymphoid periphery by T cells that undergo early TCR{alpha} rearrangements

A sparse population of thymocytes undergoes TCRalpha gene rearrangement early in development, before the double-positive stage. The potential of these cells to contribute to the peripheral T cell pool is unknown. To examine the peripheral T cell compartment expressing a repertoire biased to early TCR gene rearrangements, we developed a mouse model in which TCRalpha rearrangements are restricted to the double-negative stage of thymocyte development. These mice carry floxed RAG2 alleles and a Cre transgene driven by the CD4 promoter. As expected, conventional T cell development is compromised in such Cre(+) RAG2(fl/fl) mice, and the TCRalphabeta(+) T cells that develop are limited in their TCRalpha repertoire, preferentially using early rearranging Valpha genes. In the gut, the Thy-1(+)TCRalphabeta(+) intraepithelial lymphocyte (IEL) compartment is surprisingly intact, whereas the Thy-1(-)TCRalphabeta(+) subset is almost completely absent. Thus, T cells expressing a TCRalpha repertoire that is the product of early gene rearrangements can preferentially populate distinct IEL compartments. Despite this capacity, Cre(+) RAG2(fl/fl) T cell progenitors cannot compete with wild-type T cell progenitors in mixed bone marrow chimeras, suggesting that in normal mice, there is only a small contribution to the peripheral T cell pool by cells that have undergone early TCRalpha rearrangements. In the absence of wild-type competitors, aggressive homeostatic proliferation in the IEL compartment can promote a relatively normal Thy-1(+) TCRalphabeta(+) T cell pool from the limited population derived from Cre(+) RAG2(fl/fl) progenitors.

Quantitative isolation of mouse and human intestinal intraepithelial lymphocytes by elutriation centrifugation

Intestinal intraepithelial lymphocytes (IEL) are specialized subsets of T cells with distinct functional capacities. While some IEL subsets are circulating, others such as CD8alphaalpha TCRalphabeta IEL are believed to represent non-circulating resident T cell subsets [Sim, G.K., Intraepithelial lymphocytes and the immune system. Adv. Immunol., 1995. 58: 297-343.]. Current methods to obtain enriched preparations of intraepithelial lymphocytes are mostly based on Percoll density gradient or magnetic bead-based technologies [Lundqvist, C., et al., Isolation of functionally active intraepithelial lymphocytes and enterocytes from human small and large intestine. J. Immunol. Methods, 1992. 152(2): 253-263.]. However, these techniques are hampered by a generally low yield of isolated cells, and potential artifacts due to the interference of the isolation procedure with subsequent functional assays, in particular, when antibodies against cell surface markers are required. Here we describe a new method for obtaining relatively pure populations of intestinal IEL (55-75%) at a high yield (>85%) by elutriation centrifugation. This technique is equally suited for the isolation and enrichment of intraepithelial lymphocytes of both mouse and human origin. Time requirements for fractionating cell suspensions by elutriation centrifugation are comparable to Percoll-, or MACS-based isolation procedures. Hence, the substantially higher yield and the consistent robust enrichment for intraepithelial lymphocytes, together with the gentle treatment of the cells during elutriation that does not interfere with subsequent functional assays, are important aspects that are in favor of using this elegant technology to obtain unmanipulated, unbiased populations of intestinal intraepithelial lymphocytes, and, if desired, also of pure epithelial cells.

Developing an HIV cytotoxic T-lymphocyte vaccine: issues of CD8 T-cell quantity, quality and location

Issues of quantity, quality and location impact the ability of CD8 T cells to mediate protection from infection. These issues are considered in light of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) vaccination. Methods are reviewed that result in 100- to 1000-fold higher frequencies of vaccine-specific memory CD8 T cells than that achieved by current HIV/SIV vaccine approaches. Data demonstrating that location within mucosal tissues has a direct impact on memory CD8 T-cell function are discussed. Arguments are made that establishing memory CD8 T cells within mucosal sites of transmission, a priori to natural infection, may be essential for conferring optimal and rapid protection. Lastly, it is proposed that heterologous prime-boost vaccination with recombinant live replicating vectors, which has the potential to induce tremendous numbers of cytolytic memory CD8 T cells within mucosal tissues, would provide a far more stringent test of the hypothesis that memory CD8 T cells could, in principal, form the basis for a preventative HIV vaccine.

CCR2 receptor is essential to activate microbicidal mechanisms to control Toxoplasma gondii infection in the central nervous system

Chemokines comprise a structurally related family of cytokines that regulate leukocyte trafficking. Because infection with Toxoplasma gondii can induce an important inflammatory reaction that, if left uncontrolled, can lead to death, we investigated the role of the chemokine receptor CCR2 in T. gondii infection. We orally infected CCR2(-/-) mice with five ME-49 T. gondii cysts and monitored morbidity, survival, and immune response thereafter. The CCR2(-/-) mice displayed higher susceptibility to infection as all mice died on day 28 after infection. Despite similar Th1 responses, a more evident anti-inflammatory response was induced in the peripheral organs of CCR2(-/-) mice compared with wild-type C57BL/6 mice. Additionally, CCR2(-/-) mice presented greater parasitism and a milder inflammatory reaction in their peripheral organs with lesser CD4(+) and MAC-1(+) and greater CD8(+) cell migration. The parasite load decreased in these organs in CCR2(-/-) mice but remained uncontrolled in the central nervous system. Additionally, we observed down-regulated inducible nitric oxide synthase expression in peripheral organs from CCR2(-/-) mice that was associated with a small nitric oxide production by spleen macrophages. In conclusion, in the absence of CCR2, another mechanism is activated to control tissue parasitism in peripheral organs. Nevertheless, CCR2 is essential for the activation of microbicidal mediators that control T. gondii replication in the central nervous system.

Modulation of mucosal immunity in a murine model of food-induced intestinal inflammation

BACKGROUND

Hypersensitivity or uncontrolled responses against dietary antigens can lead to inflammatory disorders like food allergy and current models reflect a variety of causes but do not reveal the detailed modulation of gut immunity in response to food antigens after breakdown in mucosal tolerance.

OBJECTIVE

To develop and characterize a murine model for food-induced intestinal inflammation and to demonstrate the modulation of gut immune response by dietary allergenic antigens.

METHODS

C57BL/6 mice were sensitized with peanut proteins, challenged with peanut seeds and their sera and gut segments were collected for subsequent analyses.

RESULTS

Sensitization and challenged with peanut seeds led to alterations in gut architecture with inflammatory response characterized by oedema in lamina propria and cell infiltrate composed mainly by eosinophils, mast cells, phagocytes, natural killer and plasma cells, together with low percentage of gammadelta+ and CD4+CD25+Foxp3+ cells in Peyer's patches. These animals also presented high levels of specific IgE and IgG1 in sera and modulation of mucosal immunity was mediated by increased expression of GATA-3, IL-4, IL-13 and TNF-alpha in contrast to low IFN-gamma in the gut.

CONCLUSION

A murine model for food-induced intestinal inflammation was characterized in which modulation of gut immunity occurs by peanut antigens in consequence of T-helper type 2 (Th2) allergic response and failure of regulatory mechanisms necessary for mucosa homeostasis, resembling food allergy. This work shed some light on the understanding of the pathogenesis of gastrointestinal disorders and intolerance in the gut and supports the development of therapies for food-related enteropathies like food allergy, focusing on gut-specific immune response.

IFN-gamma-producing dendritic cells are important for priming of gut intraepithelial lymphocyte response against intracellular parasitic infection

The importance of intraepithelial lymphocytes (IEL) in immunoprotection against orally acquired pathogens is being increasingly recognized. Recent studies have demonstrated that Ag-specific IEL can be generated and can provide an important first line of defense against pathogens acquired via oral route. However, the mechanism involved in priming of IEL remains elusive. Our current study, using a microsporidial model of infection, demonstrates that priming of IEL is dependent on IFN-gamma-producing dendritic cells (DC) from mucosal sites. DC from mice lacking the IFN-gamma gene are unable to prime IEL, resulting in failure of these cells to proliferate and lyse pathogen-infected targets. Also, treatment of wild-type DC from Peyer's patches with Ab to IFN-gamma abrogates their ability to prime an IEL response against Encephalitozoon cuniculi in vitro. Moreover, when incubated with activated DC from IFN-gamma knockout mice, splenic CD8(+) T cells are not primed efficiently and exhibit reduced ability to home to the gut compartment. These data strongly suggest that IFN-gamma-producing DC from mucosal sites play an important role in the generation of an Ag-specific IEL response in the small intestine. To our knowledge, this report is the first demonstrating a role for IFN-gamma-producing DC from Peyer's patches in the development of Ag-specific IEL population and their trafficking to the gut epithelium.

Antigen receptor V-segment usage in mucosal T cells

In the accepted model of lymphocyte intestinal homing, naïve T cells recirculate via organized lymphoid tissues, whilst induced effector/memory cells home to the intestinal mucosa. In order to assess the T-cell-receptor repertoire in the intestine and gut-associated lymphoid tissue (GALT), spectratyping was performed on the proximal and the distal intestine, spleen and mesenteric lymph node tissue from six PVG rats. The products were analysed with an automated sequencer and statistical analyses were performed with hierarchical cluster analysis. This demonstrated the presence of a restricted T-cell repertoire in the small intestine compared with that in the mesenteric lymph nodes and the spleen. It also demonstrated marked differences in repertoire between individual, fully inbred rats maintained under apparently identical conditions in the same cage and fed identical diets. In addition, this work demonstrated marked differences between repertoires in the proximal and the distal intestine. Such marked differences are likely to reflect the end result of increasing divergence over time produced by relatively subtle effects of environment and antigenic load. Equally, marked differences in repertoire between small intestinal segments within individual rats indicate selective recruitment or retention of specific clones, presumably antigen-driven.

Impaired accumulation of antigen-specific CD8 lymphocytes in chemokine CCL25-deficient intestinal epithelium and lamina propria

CCL25 and CCR9 constitute a chemokine/receptor pair involved in T cell development and in gut-associated immune responses. In this study, we generated CCL25(-/-) mice to answer questions that could not be addressed with existing CCR9(-/-) mice. Similar phenotypes were observed for both CCL25(-/-) and CCR9(-/-) mice, consistent with the notion that CCL25 and CCR9 interact with each other exclusively. We assessed the requirement for CCL25 in generating CCR9(high) CD8 intestinal memory-phenotype T cells and the subsequent accumulation of these cells within effector sites. TCR-transgenic naive CD8 T cells were transferred into wild-type or CCL25-deficient hosts. Oral sensitization with Ag allowed these naive donor cells to efficiently differentiate into CCR9(high) memory-phenotype cells within the mesenteric lymph nodes of wild-type hosts. This differentiation event occurred with equal efficiency in the MLN of CCL25-deficient hosts, demonstrating that CCL25 is not required to induce the CCR9(high) memory phenotype in vivo. However, we found that CCL25 deficiency severely impaired the Ag-dependent accumulation of donor-derived CD8 T cells within both lamina propria and epithelium of the small intestine. Thus, although CCL25 is not necessary for generating memory-phenotype CD8 T cells with "gut-homing" properties, this chemokine is indispensable for their trafficking to the small intestine.

Recognition of double-stranded RNA by TLR3 induces severe small intestinal injury in mice

The role of TLRs on intestinal epithelial cells (IECs) is controversial, and the mechanisms by which TLRs influence mucosal homeostasis are obscure. In this study, we report that genomic dsRNA from rotavirus, and its synthetic analog polyinosinic-polycytidylic acid (poly(I:C)), induce severe mucosal injury in the small intestine. Upon engaging TLR3 on IECs, dsRNA triggers IECs to secrete IL-15, which functions to increase the percentage of CD3+NK1.1+ intestinal intraepithelial lymphocytes (IELs) and enhances the cytotoxicity of IELs. Moreover, The CD3+NK1.1+ IELs are proved as CD8alphaalpha+ IELs. These results provide direct evidence that abnormal TLR3 signaling contributes to breaking down mucosal homeostasis and the first evidence of pathogenic effects mediated by CD8alphaalpha+ IELs. The data also suggest that genomic dsRNA may be involved in the pathogenesis of acute rotavirus gastroenteritis.

CCR4-dependent regulatory T cell function in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an idiopathic inflammatory disease of the intestine. CD4⁺ T lymphocytes play an important role in both initiating and regulating intestinal inflammatory immune responses. CD4⁺CD25⁺CD45RB^low regulatory T (T reg) cells are capable of preventing the development of colitis in a mouse model of IBD. The precise mechanism of T reg cell–mediated prevention of colitis in this model is unclear, and the role of chemokine receptors in the trafficking and function of T reg cells in this model has not been determined. We examined the role of the chemokine receptor CCR4 in in vivo trafficking and suppressive function of T reg cells in a mouse adoptive transfer model of IBD. CCR4-deficient T reg cells failed to accumulate in the mesenteric lymph nodes (MLNs) at early time points (2–5 d) after adoptive transfer, resulting in a failure to suppress the generation of pathogenic T cells and the development of colitis. Moreover, although CCR4-deficent T cells had equivalent in vitro suppressive activity and accumulated in MLNs at later time points (42–56 d), they were unable to suppress colitis. Our study demonstrates that CCR4 plays an important role in T reg cell trafficking in LNs and that this is critical for T reg cell suppressive function in vivo.

Intraepithelial lymphocytes: their shared and divergent immunological behaviors in the small and large intestine

At the front line of the body's immunological defense system, the gastrointestinal tract faces a large number of food-derived antigens, allergens, and nutrients, as well as commensal and pathogenic microorganisms. To maintain intestinal homeostasis, the gut immune system regulates two opposite immunological reactions: immune activation and quiescence. With their versatile immunological features, intraepithelial lymphocytes (IELs) play an important role in this regulation. IELs are mainly composed of T cells, but these T cells are immunologically distinct from peripheral T cells. Not only do IELs differ immunologically from peripheral T cells but they are also comprised of heterogeneous populations showing different phenotypes and immunological functions, as well as trafficking and developmental pathways. Though IELs in the small and large intestine share common features, they have also developed differences as they adjust to the two different environments. This review seeks to shed light on the immunological diversity of small and large intestinal IELs.

Generation of gut-homing T cells and their localization to the small intestinal mucosa

The intestinal mucosa represents the largest body surface toward the external environment and harbors numerous T lymphocytes that take up resident within the intestinal epithelium or in the underlying lamina propria (LP). The intraepithelial lymphocytes include subsets of 'unconventional' T cells with unclear ontogeny and reactivity that localize to this site independently of antigen-specific activation in secondary lymphoid organs. In contrast, the majority of the 'conventional' gut T cells are recruited into the intestinal mucosa subsequent to their activation in intestinal inductive sites, including Peyer's patches (PPs) and mesenteric lymph nodes (MLNs). T cells homing to the small intestine express a distinct pattern of homing molecules, allowing them to interact with and transmigrate across intestinal postcapillary endothelium. At least some of these homing molecules, including the integrin alpha(4)beta(7) and the chemokine receptor CCR9, are induced on T cells during their activation in PPs or MLNs. Mucosal dendritic cells (DCs) play a key role in this process, but not all intestinal DCs possess the ability to confer a gut-homing capacity to T cells. Instead, functionally specialized CD103(+) DCs derived from the small intestinal LP appear to selectively regulate T-cell homing to the small intestine.

Thymic differentiation of TCRαβ+CD8αα+IELs

Intraepithelial lymphocytes (IELs) contain several subsets, but the origin of the T-cell receptor (TCR)alphabeta(+) CD8 alpha alpha(+) IELs has been particularly controversial. Here we provide a synthesis, based on recent work, that attempts to unify the divergent views. The intestine has a primordial function in lymphopoiesis, and precursors with the potential to differentiate into T cells are found both in the epithelium and underlying lamina propria. Moreover, the thymus has been reported to export cells to the intestine that are not fully differentiated. TCR alpha beta(+) CD8 alpha alpha(+) IELs can differentiate in the intestine from each of these sources, but in normal euthymic mice, the thymus appears to be the major source for TCR alpha beta(+) CD8 alpha alpha(+) IELs. This unique IEL subset is a self-reactive population that requires exposure to self-agonists for selection in the thymus, similar to other regulatory T-cell populations. IELs transition through a double-positive (DP) intermediate in the thymus, but they originate from a subset of the DP cells that can be identified by its expression of CD8 alpha alpha homodimers. The agonist-selected cells in the thymus are TCRbeta(+) but CD4 and CD8 double negative. The evidence suggests that reacquired expression of CD8 alpha alpha and downregulation of CD5 occur after thymus export, perhaps in the intestine under the influence of interleukin-15. As a result of agonist exposure, a new gene expression program is activated. Therefore, the increased understanding of the developmental origin of TCR alpha beta(+) CD8 alpha alpha(+) IELs may help us to understand how they participate in immune regulation and protection in the intestine.

Massive, sustained γδ T cell migration from the bovine skin in vivo

In all species studied so far, gammadelta T cells are abundantly present in epithelia. The functions of these cells are largely unknown. Using a lymph duct cannulation method, which is only possible in large animals such as cattle, we show that large numbers of gammadelta T cells, but not alphabeta T cells, are constitutively present in pseudoafferent lymph draining bovine skin. The gammadelta T cells, which are present in pseudoafferent lymph, use Vgamma segments that are characteristic for bovine dermal gammadelta T cells, suggesting that these cells migrated from the skin. Further supporting the origin of these cells is the fact that fluorescent latex beads injected in the skin could be recovered in cells in the pseudoafferent lymph. The cannulation method is minimally invasive, and the lymph flow, which was sustained and remained essentially unaltered during 14 days, closely represents the in vivo situation. The gammadelta T cells could not be induced to produce IFN-gamma, TNF-alpha, and IL-10, and they did not express costimulatory molecules, IL-2 receptor, and MHC Class II molecules. The level of gammadelta T cell egress was 6.7x10(3) gammadelta T cells per cm2 skin per hour, which is enough to deplete all gammadelta T cells from the skin within 46 h. As this massive gammadelta T cell migration was observed during 14 days, constant replenishment of these cells must take place. Our data suggest that gammadelta T cells in tissues fulfill more than exclusively local functions.

The effect of weaning on the clonality of alpha beta T-cell receptor T cells in the intestine of GF and SPF mice

In humans, intestinal antigen exposure during neonatal life influences the T-cell receptor (TCR) repertoire. To define the relative effects of bacteria and food antigens in early life, we examined TCR diversity in the intestine of SPF and GF mice. TCR repertoire was assessed at a single time point pre-, peri- and post-weaning in the small and large intestine of SPF and GF mice using spectratyping and/or TCR-beta-chain sequencing. There was good concordance of data obtained by the two techniques. In SPF mice, the repertoire was polyclonal shortly after birth in the small and large intestine. After weaning, there was a significant change towards an oligoclonal repertoire in the small intestine. There was some evidence that specific clones were shared between the small and large intestine. In contrast, in GF mice, the repertoire was oligoclonal after birth, and remained restricted. These data show: firstly, that under SPF conditions, the intestine is seeded with a diverse T-cell population that becomes oligoclonal around the time of weaning; secondly, that GF mice were oligoclonal at each time point.

CD8 alpha alpha-mediated intraepithelial lymphocyte snatching of thymic leukemia MHC class Ib molecules in vitro and in vivo

Thymic leukemia (TL) is a MHC class Ib molecule that interacts with CD8alphaalpha homodimers. CD8alphaalpha is abundantly expressed by intraepithelial T lymphocytes (IELs) located in close proximity to TL-expressing intestinal epithelial cells. In this study, we show that CD8alphaalpha(+) IELs "snatch" TL from the plasma membrane of TL-expressing cells and express TL in its proper orientation on their own cell surface. TL snatching is enhanced by cross-linking of IEL TCRs in a phosphatidylinositol kinase-dependent manner, and results in overall alterations to the IEL cell surface detected by enhanced binding of peanut agglutinin lectin. Induction of bowel inflammation results in the presence of TL on IELs, probably via in vivo snatching, providing the initial evidence for the interaction of CD8alphaalpha IELs with intestinal cells.

TLR9 is required for the gut-associated lymphoid tissue response following oral infection of Toxoplasma gondii

TLRs expressed by a variety of cells, including epithelial cells, B cells, and dendritic cells, are important initiators of the immune response following stimulation with various microbial products. Several of the TLRs require the adaptor protein, MyD88, which is an important mediator for the immune response following Toxoplasma gondii infection. Previously, TLR9-mediated innate immune responses were predominantly associated with ligation of unmethylated bacterial CpG DNA. In this study, we show that TLR9 is required for the Th1-type inflammatory response that ensues following oral infection with T. gondii. After oral infection with T. gondii, susceptible wild-type (WT; C57BL/6) but not TLR9(-/-) (B6 background) mice develop a Th1-dependent acute lethal ileitis; TLR9(-/-) mice have higher parasite burdens than control WT mice, consistent with depressed IFN-gamma-dependent parasite killing. A reduction in the total T cell and IFN-gamma-producing T cell frequencies was observed in the lamina propria of the TLR9(-/-) parasite-infected mice. TLR9 and type I IFN production was observed by cells from infected intestines in WT mice. TLR9 expression by dendritic cell populations is essential for their expansion in the mesenteric lymph nodes of infected mice. Infection of chimeric mice deleted of TLR9 in either the hemopoietic or nonhemopoietic compartments demonstrated that TLR9 expression by cells from both compartments is important for efficient T cell responses to oral infection. These observations demonstrate that TLR9 mediates the innate response to oral parasite infection and is involved in the development of an effective Th1-type immune response.

A ticket to the gut for thymic T cells

The intestinal epithelium is colonised by, among other cells, normal T helper and cytotoxic T cells which obtain their antigen experience in the gut associated lymphatics after migration from the thymus. New evidence suggests a CD8 positive T cell that directly migrates to the intestinal epithelium increasing the role of the thymus in shaping intestinal immunity