Intestinal Intraepithelial Lymphocytes Subsets Research Articles

Intraepithelial Lymphocytes of the Intestine.

The intestinal epithelium, which segregates the highly stimulatory lumen from the underlying tissue, harbors one of the largest lymphocyte populations in the body, intestinal intraepithelial lymphocytes (IELs). IELs must balance tolerance, resistance, and tissue protection to maintain epithelial homeostasis and barrier integrity. This review discusses the ontogeny, environmental imprinting, Tcell receptor (TCR) repertoire, and function of intestinal IELs. Despite distinct developmental pathways, IEL subsets share core traits including an epithelium-adapted profile, innate-like properties, cytotoxic potential, and limited TCR diversity. IELs also receive important developmental and functional cues through interactions with epithelial cells, microbiota, and dietary components. The restricted TCR diversity of IELs suggests that a limited set of intestinal antigens drives IEL responses, with potential functional consequences. Finally, IELs play a key role in promoting homeostatic immunity and epithelial barrier integrity but can become pathogenic upon dysregulation. Therefore, IELs represent intriguing but underexamined therapeutic targets for inflammatory diseases and cancer. Expected final online publication date for the Annual Review of Immunology, Volume 42 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The role of intestinal intraepithelial lymphocytes in resistance against coccidiosis in chickens

Abstract Coccidiosis is a critical enteric disease that costs more than $14.5 billion in annual cost to world poultry industry. It is caused by different Eimeriaspecies that invade and replicate within the intestinal epithelium in a site-specific manner. The Eimeriainfection induces local intestinal damage, reduces feed consumption, feed utilization, and growth performance, and increasing mortality rate. With the recent antibiotic ban including anticoccidial drugs in chicken production, the live vaccination become widely used to control coccidiosis. However, the live vaccines are expensive, require time to circulate in the host to induce a protective immunity, and process a high-risk factor for necrotic enteritis caused by clostridium perfringens. Therefore, there is a high demand for development of safe, protective, and inexpensive vaccines against coccidiosis which require better understanding of host immune responses to Eimeria parasites. The aim of this study is to elucidate the protective role of intestinal intraepithelial lymphocytes (IELs) during the Eimeriainfection. At 3 week of age, SPF white-leghorn chicks were divided into 3 groups. Each group (n=50) was orally inoculated with 20,000 oocytes of Eimeria (E) acervuline or E. maxima, or mock-inoculated with PBS. At 2 day post-infection (dpi), 7 dpi and 14 dpi, the frequency and the number of small intestinal IEL populations were determined by a flow cytometry. Eimeriainfection induced the number of TCRγδ +, TCRβ +, TCR neg, TCRβ +CD4 +, TCRβ +CD4 +CD8α +, TCRβ +CD8αβ +, TCRβ +CD8αα +, and iCD8α IELs compared to the control group at 14 dpi. However, there was no difference among groups at 2 and 7 dpi. More experiments are underway to determine the effector and function of each subset of IELs. Startup funding, The OSU

Development and function of natural TCR+ CD8αα+ intraepithelial lymphocytes.

The complexity of intestinal homeostasis results from the ability of the intestinal epithelium to absorb nutrients, harbor multiple external and internal antigens, and accommodate diverse immune cells. Intestinal intraepithelial lymphocytes (IELs) are a unique cell population embedded within the intestinal epithelial layer, contributing to the formation of the mucosal epithelial barrier and serving as a first-line defense against microbial invasion. TCRαβ+ CD4- CD8αα+ CD8αβ- and TCRγδ+ CD4- CD8αα+ CD8αβ- IELs are the two predominant subsets of natural IELs. These cells play an essential role in various intestinal diseases, such as infections and inflammatory diseases, and act as immune regulators in the gut. However, their developmental and functional patterns are extremely distinct, and the mechanisms underlying their development and migration to the intestine are not fully understood. One example is that Bcl-2 promotes the survival of thymic precursors of IELs. Mature TCRαβ+ CD4- CD8αα+ CD8αβ- IELs seem to be involved in immune regulation, while TCRγδ+ CD4- CD8αα+ CD8αβ- IELs might be involved in immune surveillance by promoting homeostasis of host microbiota, protecting and restoring the integrity of mucosal epithelium, inhibiting microbiota invasion, and limiting excessive inflammation. In this review, we elucidated and organized effectively the functions and development of these cells to guide future studies in this field. We also discussed key scientific questions that need to be addressed in this area.

Intestinal intraepithelial lymphocyte repertoires are imprinted clonal structures selected for MHC reactivity

Abstract The intestinal mucosa is an important barrier for maintaining homeostasis and immune tolerance. Residing in the gut mucosa are the intestinal intraepithelial lymphocytes (IELs), an unconventional T cell type expressing αβ T cell receptors (TCRs) thought to contribute in immune surveillance and mediate repair of damaged epithelium. IELs are in close contact with a stream of microbial, food, and self-antigens, and while TCR-antigen interaction is presumed the major mechanism governing their functions, little is known about the native TCRαβ-IEL repertoire or its specificity. Previously, we developed a nearest-neighbor distance measurement (TCRdist) for quantifying convergence within TCR repertoires based on enriched features within their determinants of specificity. Here, we extended TCRdist to develop two novel tools for repertoire analysis: RepDist, for measuring similarity between repertoires, and TStar, for identifying repertoire-enriched features. We applied these to conduct a survey of the ‘normal’ TCR repertoires for three major subsets (CD8αα+, CD8, CD4) of IELs, under varying conditions of microbiome depletion, food antigen deprivation, MHC-deficiency, and combinations thereof. Surprisingly, the only perturbations that disrupted the IEL repertoire were deficiencies in Class I molecules or β2m. Food antigen and microbiome depletion had virtually no effect on the clonotypic composition of all three IEL subsets. MHC-substitution also had little effect, indicating that while Class I is required for CD8αα and CD8 IEL selection, it is haplotype-independent. Taken together, these data demonstrate the native IEL TCR repertoires are selected for self-reactivity, rather than specificity towards exogenous antigens.

Intestinal Intraepithelial Lymphocyte Repertoires are Imprinted Clonal Structures Selected for MHC Reactivity

Intestinal intraepithelial lymphocytes (IELs) form an unconventional T cell population demarcated by agonistic selection in the thymus before populating the gut mucosa, where it is thought they contribute in surveillance, homeostasis, and epithelial repair. Although IELs have been implicated in diseases affecting the gut, much remains to be understood about their selection and specificity. Integrating T cell receptor (TCR) repertoire sequencing and transcriptional profiling, we identify characteristic TCR features of induced CD4-, CD8-, and natural-IEL subsets and furthermore describe for the first time the human natural IEL subset. Depletion of microbial and dietary antigens alone or in combination did little to affect the underlying structure of each subset’s TCR repertoire. In contrast, disruption of β2m-dependent pathways abrogated public features that distinguished the natural IEL repertoires. These findings support a model for imprinting of TCRαβ-IEL repertoires based on competition among similar clonotypes selected for specificity to ubiquitous, conserved, β2m-dependent self-antigens.

Phenotypic characterization of canine intestinal intraepithelial lymphocytes in dogs with inflammatory bowel disease.

BackgroundMany dogs suffering from inflammatory bowel disease (IBD) are presented to veterinary clinics. These patients are diagnosed based on a history of chronic gastrointestinal signs and biopsy‐confirmed histopathologic intestinal inflammation. Intestinal intraepithelial lymphocytes (IEL) are part of the first line of defense in the gastrointestinal immune system. Alterations in IEL subsets may play a role in the pathogenesis of IBD.HypothesisThe aim of this study was to characterize the phenotypes of IEL in dogs with IBD compared with healthy control dogs.AnimalsIntestinal intraepithelial lymphocytes subpopulations of control dogs (n = 5) obtained from endoscopic biopsies (EB) were compared to those obtained from full thickness biopsies (FTB) on the same day. In addition, the phenotypes of IEL from FTB of control dogs (n = 10) were compared with EB of IBD dogs (n = 10). Each participant was scored clinically using the canine inflammatory bowel disease activity index (CIBDAI), and all samples were graded histopathologically. Three‐color flow cytometry of isolated IEL was performed using monoclonal antibodies against T‐ and B‐lymphocyte subpopulations.ResultsNo significant differences in the composition of IEL subpopulations were found in control dogs based on method of biopsy. The IBD dogs had significantly higher CIBDAI and histopathologic scores compared with control dogs and their IEL contained a significantly higher frequency TCRγδ T‐cells.Conclusions and Clinical ImportanceEndoscopic biopsies provide suitable samples for 3‐color flow cytometry when studying canine intestinal IEL and IBD patients show significant changes of major T‐cell subsets compared to healthy control dogs.

Glutamine modulates CD8αα+ TCRαβ+ intestinal intraepithelial lymphocyte expression in mice with polymicrobial sepsis

ObjectivesCD8αα+ T-cell receptor (TCR) αβ+ intestinal intraepithelial lymphocytes (IELs) were found to have a regulatory function in the mucosal immune system. Glutamine (GLN) is an amino acid with immunomodulatory effects. The aim of this study was to investigate the influences of GLN on the proportion of CD8αα+ TCRαβ+ IELs and associated inflammatory mediator gene expression in polymicrobial sepsis. MethodsMice were randomly assigned to a normal (NC) group, a sepsis with saline (SS) group, or a sepsis with GLN (SG) group. The NC group was fed a chow diet. Sepsis was induced by cecal ligation and puncture (CLP). The SS group was administered saline, and the SG group was given 0.75 g GLN/kg body weight via a tail vein after CLP. Mice were sacrificed 12 h after CLP, and CD8αα+ TCRαβ+ IELs were isolated for further analysis. ResultsSepsis resulted in a lower percentage of CD8αα+ TCRαβ+ IELs, and higher messenger (m)RNA expression of complement 5a receptor, interleukin (IL)-2 receptor β, IL-15 receptor α, and interferon-γ by CD8αα+ TCRαβ+ IELs. These immunomodulatory mediator genes decreased, whereas IL-7 receptor and transforming growth factor-β expressions increased in CD8αα+ TCRαβ+ IELs in septic mice with GLN administration. Annexin V⁄7-AAD staining revealed significantly lower apoptotic rates of CD8αα+ TCRαβ+ IELs in the SG group. ConclusionA single dose of GLN administered after the initiation of sepsis increased the percentage of CD8αα+ TCRαβ+ IELs, prevented apoptosis of CD8αα+ TCRαβ+ IELs, and downregulated CD8αα+ TCRαβ+ IEL-expressed inflammatory mediators. These results suggest that GLN influenced the distribution and cytokine secretion of the CD8αα+ TCRαβ+ IEL subset, which may ameliorate sepsis-induced inflammatory reactions and thus mitigate the severity of intestinal epithelial injury.

Production of interferon‐γ by activated T‐cell receptor‐αβ CD8αβ intestinal intraepithelial lymphocytes is required and sufficient for disruption of the intestinal barrier integrity

Maintenance of intestinal epithelial barrier function is of vital importance in preventing uncontrolled influx of antigens and the potentially ensuing inflammatory disorders. Intestinal intraepithelial lymphocytes (IEL) are in intimate contact with epithelial cells and may critically regulate the epithelial barrier integrity. While a preserving impact has been ascribed to the T-cell receptor (TCR)-gammadelta subset of IEL, IEL have also been shown to attenuate the barrier function. The present study sought to clarify the effects of IEL by specifically investigating the influence of the TCR-alphabeta CD8alphabeta and TCR-alphabeta CD8alphaalpha subsets of IEL on the intestinal epithelial barrier integrity. To this end, an in vitro coculture system of the murine intestinal crypt-derived cell-line mIC(cl2) and syngeneic ex vivo isolated IEL was employed. Epithelial integrity was assessed by analysis of transepithelial resistance (TER) and paracellular flux of fluorescein isothiocyanate-conjugated (FITC-) dextran. The TCR-alphabeta CD8alphaalpha IEL and resting TCR-alphabeta CD8alphabeta IEL did not affect TER of mIC(cl2) or flux of FITC-dextran. In contrast, activated TCR-alphabeta CD8alphabeta IEL clearly disrupted the integrity of the mIC(cl2) monolayer. No disrupting effect was seen with activated TCR-alphabeta CD8alphabeta IEL from interferon-gamma knockout mice. These findings demonstrate that secretion of interferon-gamma by activated TCR-alphabeta CD8alphabeta IEL is strictly required and also sufficient for disrupting the intestinal epithelial barrier function.

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 CD8αα TCRαβ 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.

Glutamine supplementation increases Th1-cytokine responses in murine intestinal intraepithelial lymphocytes

Intestinal intraepithelial lymphocytes (IELs) are major effector cells in the gut mucosal immune system, and are phenotypically distinct from thymic and peripheral T cells. Although nutritional supplementation with glutamine affects the intestinal immune response, it remains unclear whether this is a direct effect via the IEL-derived cytokines. This study examined changes in IEL-derived cytokine production following treatment with glutamine in vitro. Murine IELs were purified and activated with PMA plus ionomycin, and then cultured in the presence of various glutamine concentrations. IEL-derived cytokines were measured using a cytometric bead array (CBA) system, and IEL subsets were analyzed by flow cytometry. Treatment with glutamine increased the production of IL-2 and IFN-γ from IELs in the presence of PMA plus ionomycin, but had no effect on TNFα, IL-4, or IL-5 production. Treatment with alanine or glucose had no regulatory effect on IEL-derived cytokines. Glutamine therefore had a direct effect on the production of selected IEL-derived Th1-cytokines, and enteral supplementation with glutamine may influence the intestinal immune responses mediated by IELs.

Stimulatory and costimulatory effects of IL-18 directed to different small intestinal CD43 T cell subsets

This study has examined the stimulatory and costimulatory effects of IL-18 on two subsets of murine small intestinal intraepithelial lymphocytes (IELs) defined by the expression of the CD43 S7 glycoform. Data from gene array studies and real-time PCR indicated that S7(+) IELs had significantly higher levels of gene expression for the IL-18 receptor and the IL-18R accessory protein than S7(-) IELs. IL-18 costimulation of IELs in conjunction with CD3-induced activation resulted in significantly greater proliferation than CD3 stimulation alone. In CFSE dilution experiments, IL-18 costimulation favored the S7(+) IEL population. IL-18 costimulation did not affect apoptosis of either S7(-) or S7(+) IELs compared with CD3 stimulation alone. Although IL-18 costimulation did not alter the total number of IFN-gamma-producing cells relative to CD3 stimulation alone, twice as many S7(+) IELs were IFN-gamma -secreting cells than S7(-) IELs in both CD3-stimulated and IL-18-costimulated cultures. Notably, direct IL-18 stimulation in the absence of CD3 activation induced an IFN-gamma response that was predominantly directed to the S7(+) population, indicating that IL-18 is itself an IFN-gamma activational signal for intestinal T cells. In contrast, direct IL-18 stimulation of IELs did not generate TNF-alpha-producing cells, indicating a differential response in the activation of proinflammatory cytokines following IL-18 exposure. These findings point to distinctly different activational effects of IL-18 on IELs, both with regard to the type of functional responses elicited and with respect to the IEL subsets affected.

Comprehensive phenotypic analysis of the gut intra-epithelial lymphocyte compartment: perturbations induced by acute reovirus 1/L infection of the gastrointestinal tract

Intestinal intra-epithelial lymphocytes (IELs) form a highly specialized lymphoid compartment. IELs consist primarily of T cells that are dispersed as single cells within the epithelial cell layer that surrounds the intestinal lumen. These lymphocytes along with lamina propria lymphocytes are considered to play an important role in the regulation of immune responses. IELs are heterogeneous with regard to phenotype, and they contain sub-populations with diverse functions. In our most recent study, we found that intra-duodenal inoculation of mice with reovirus serotype 1/strain Lang (reovirus 1/L) induced expression of both germinal center and T cell antigen and CD11c on IELs suggesting these cells to be the recently stimulated cells in gut mucosal tissue. We also demonstrated that IELs from these mice when cultured in vitro in the presence of reovirus 1/L-pulsed antigen-presenting cells generated reovirus 1/L-specific MHC-restricted CTL whose function was mediated utilizing perforin, Fas-FasL and TRAIL mechanisms. This present study provides a comprehensive analysis of the diverse subsets of IELs, which function with other mucosal cells to provide a strong, protective immunity in a highly regulated fashion inside the microenvironment of the intestinal epithelium. We demonstrated that the IEL population contains both thymus-dependent (TD) and thymus-independent (TI) lymphocytes in mice and that a complex phenotype is present when sub-populations are analyzed for TCR, Thy-1, CD4, CD8 and B220 expression in a comprehensive manner. In reovirus 1/L-inoculated mice, we found a decrease in the TI population and an increase in the TD population characterized by significant alterations in various sub-populations. This increase was largely due to an increase in CD4(+), CD8(+) and CD4/CD8 double-positive sub-populations of TD IELs. Intracellular cytokine analysis demonstrated induction of IFN-gamma and an increase in effector/cytotoxic CD8 and CD4 cells after reovirus 1/L infection. These results suggest that TD IELs may play an important role in the clearance of reovirus 1/L infection from gut.

Age-Related Variation of Intraepithelial Lymphocytes Subsets in Normal Human Duodenal Mucosa

The enumeration of intestinal intraepithelial lymphocytes (IELs), and the phenotyping of CD3+CD 103+ (TcRalphabeta, TcRgammadelta) and CD3-CD103+ IEL subsets constitute useful diagnostic tools for the correct interpretation of the mucosal histology of duodenal/jejunal biopsies in many pathological conditions of the small intestine, particularly celiac disease (CD). This work evaluates the ranges of duodenal IEL counts by flow cytometry in healthy mucosa from pediatric and adult controls, establishing normal reference values for CD3+ TcRgammadelta and CD3- subsets and their variation with age. Seventy-four pediatric controls and 36 adult controls were identified on the basis of their normal histology from more than 1,000 duodenal diagnostic biopsies performed in Caucasian subjects. Total IEL counts and IEL subsets ("IEL lymphogram") were analyzed by four-color flow cytometry (FCM). IEL represent 7.7% +/- 0.4 (mean +/- SE) and 8.5% +/- 0.5 of the cells isolated from the epithelium in the pediatric and adult series, respectively. The upper normal range, considered as the 97 percentile, is 14% in pediatrics and 15% in adults. No significant difference was observed between TcRgammadeltaIEL percentages in children (6.9% +/- 0.5 of the total IELs) and adults (6.6% +/- 0.8). However, the density of CD3- IELs is significantly higher (p < 0.001) in the mucosa from controls under 3 years (50.2% +/- 2.6) than in adults (25.5% +/- 2.1). IEL lymphogram by flow cytometry is an easy, quick and reliable analysis performed in one of the biopsy specimens obtained during a diagnostic endoscopy, and confers specificity to the histopathological findings. IEL counts below 14% in children and 15% in adults should be considered within a normal range in the evaluation of duodenal mucosa by FCM. No differences with age were observed with respect to TcRgammadeltaIEL, while the CD3- IEL fraction was significantly higher on children under 3 years, with a trend to increase again in the elderly.

IELs: enforcing law and order in the court of the intestinal epithelium

The intestinal intraepithelial lymphocytes (IELs) are mostly T cells dispersed as single cells within the epithelial cell layer that surrounds the intestinal lumen. IELs are, therefore, strategically located at the interface between the antigen-rich outside world and the sterile core of the body. The intestine of higher vertebrates has further evolved to harbor numerous commensal bacteria that carry out important functions for the host, and while defensive immunity can effectively protect against the invasion of pathogens, similar immune reactions against food-derived antigens or harmless colonizing bacteria can result in unnecessary and sometimes damaging immune responses. Probably as a result of this unique dilemma imposed by the gut environment, multiple subsets of IEL have differentiated, which all display characteristics of 'activated yet resting' immune cells. Despite this common feature, IELs are heterogeneous with regard to their phenotype, ontogeny, and function. In this review, we discuss the different subtypes of IELs and highlight the distinct pathways they took that led to their unique differentiation into highly specialized effector memory T cells, which provide the most effective immune protection yet in a strictly regulated fashion to preserve the integrity and vital functions of the intestinal mucosal epithelium.

IL-15 and HIV Infection: Lessons for Immunotherapy and Vaccination

IL-15 is a pleiotropic and multifunctional cytokine that has a diverse array of distinct biological effects in the body. It plays a crucial role in host defense from viral and non-viral intracellular pathogens. The cytokine is essential for the development and differentiation of NK cells and for homeostatic expansion of CD8+ memory T cells, NKT cells and certain subsets of intestinal intra-epithelial lymphocytes (iIEL). It acts as a survival factor and inhibits spontaneous apoptosis in T, B and NK cells by increasing expression of different anti-apoptotic proteins. Several studies have shown that IL-15 production is compromised in HIV-infected AIDS patients and exogenous IL-15 drastically enhances functions of immune cells from these patients. Considering these distinct immune enhancing effects, relative safety in animal models, and minimal effects on HIV replication, IL-15 may represent a better cytokine for immune reconstitution in these patients. Furthermore, IL-15 may also act as a better adjuvant in eliciting antiviral immunity in anti-HIV vaccine strategies.

Repeated Stress Suppresses Interferon-.GAMMA. Production by Murine Intestinal Intraepithelial Lymphocytes

Intestinal intraepithelial lymphocytes (IEL), one of the major effector components in the mucosal immune system, are phenotypically and functionally distinct from thymic and peripheral T cells. To investigate the effect of repeated stress on the number and function of IEL, we exposed male C3H/HeN mice to mild electric foot shock for 30 min/day for 5 consecutive days. Immediately after the final foot shock stress, the blood, spleen, thymus and small intestine of each of the mice were obtained. As a functional measure, we evaluated interferon (IFN)- gamma production by IEL, since IFN-gamma is a key immunomodulating cytokine in mucosal immune responses. Serum corticosterone level was elevated immediately after foot shock stress. There were no significant changes in the number of whole IEL and CD3+ IEL subsets after the stress. In contrast, the stress led to a significant decrease in the total number of thymocytes, particularly the reduction in the number of CD4+CD8+ thymocytes. Thymocytes expressed the highest level of intracellular glucocorticoid receptor (GR), followed by splenocytes and IEL. The foot shock stress induced a marked suppression of IFN-gamma production by IEL, when stimulated with immobilized anti-CD3 monoclonal antibody. Furthermore, corticosterone suppressed the IFN-gamma production by cultured IEL, which was prevented by Mifepristone (RU486), a GR antagonist. In summary, repeated foot shock stress did not alter the numbers of IEL and CD3+ IEL subsets, but suppressed IFN-gamma production by IEL, which was probably mediated by the elevated corticosterone. We therefore propose that stress influences host defense by suppressing the production of IFN-gamma in IEL.

Maximum Immunobioactivity of Murine Small Intestinal Intraepithelial Lymphocytes Resides in a Subpopulation of CD43+ T Cells

CD43 has been linked to many function-associated T cell activities. Using mAbs that recognize two different CD43 determinants, we show that, although mouse small intestinal intraepithelial lymphocytes (IELs) expressed the CD43 core molecule reactive with mAb R2/60, only about one-half of the total IELs-including some but not all of the TCRalphabeta and TCRgammadelta cells-expressed the CD43 S7(-) reactive determinant. CD43 S7(+) IELs secreted more IL-2, IL-4, IL-10, IL-17, and IFN-gamma following anti-CD3 stimulation, and were >4-fold more cytotoxic in fresh isolates and >16-fold more cytotoxic after anti-CD3 stimulation, than S7(-) IELs. S7(+) but not S7(-) IELs from the ileum of IL-10(-/-) mice spontaneously produced IFN-gamma. In vivo BrdU uptake by IELs in non-Ag-primed mice was greatest in the S7(+) population, indicating that significantly more S7(+) IELs than S7(-) IELs undergo cell expansion under normal homeostatic conditions. DNA microarray analyses showed that S7(+) IELs expressed higher levels of genes associated with activated T cells, whereas S7(-) IELs expressed genes used in the regulation of NK cells. These findings define two functionally distinct populations of IELs based on CD43 expression independent of TCR class, and they identify a subset of IELs that may serve as a target to better control intestinal inflammation.

Distinct cell types control lymphoid subset development by means of IL-15 and IL-15 receptor alpha expression.

IL-15 and the IL-15 receptor (IL-15R)alpha chain are essential for normal development of naive CD8 T cells, intestinal intraepithelial lymphocytes (IEL), and natural killer (NK)/NK/T cells. However, whether IL-15R alpha expression by these subsets is necessary for their production and which cell type needs to produce IL-15 to drive development are unknown. We analyzed the requirements for IL-15 and IL-15R alpha expression by bone marrow-derived or parenchymal cells for mediating lymphocyte subset development. Naive CD8 T cell development required IL-15R alpha expression by both bone marrow-derived and parenchymal cells, whereas memory-phenotype CD8 T cells required IL-15R alpha expression only by hematopoietic cells. In contrast and surprisingly, the development of IEL subsets, particularly CD8 alpha alpha Thy1(-)V gamma 5(+) T cell antigen receptor gamma delta and the CD8 alpha alpha Thy1(-) T cell antigen receptor alpha beta IEL populations, depended completely on parenchymal cell expression of IL-15R alpha and IL-15 but not IL-15R beta. In the case of NK and NK/T cell generation and maturation, expression of IL-15 and IL-15R alpha by both parenchymal and hematopoietic cells was important, although the latter played the greatest role. These results demonstrated dichotomous mechanisms by which IL-15 regulated lymphoid development, interacting with distinct cell types depending on the developmental pathway.

Thymic and intestinal intraepithelial T lymphocyte development are each regulated by theγc-dependent cytokines IL-2, IL-7, and IL-15

Both thymic and extrathymic T lineage development are characterized by cytokine-dependent regulation of complex proliferative, differentiative, and anti-apoptotic processes. The role of the γc -dependent cytokines in this program has been interpreted as limited to the activity of IL-7. However, through the analysis of double knock-out mice, which lack signaling through the IL-7R and other γ c-dependent cytokines, we revealed a role for IL-15 in the production of early thymic pro-T cells. Although IL-2 does not function in the production of thymocytes, thymic restoration of IL-2R expression prevented fatal autoimmunity associated with IL-2- or IL-2R-deficient mice, suggesting that IL-2R functions non-redundantly at the level of the thymus to regulate self-reactivity. Moreover, IL-2, IL-7, and IL-15 also extend their developmental effects beyond the thymus to other sites of T lymphocyte production, including the gut. Here, their redundant and non-redundant activities are directly correlated to the development of phenotypically diverse subsets of intestinal intraepithelial lymphocytes.

Intestinal intraepithelial lymphocytes exert potent protective cytotoxic activity during an acute virus infection.

After systemic infection of mice with 104 PFU of lymphocytic choriomeningitis virus (LCMV), infected cells are detected simultaneously in various organs, including spleen and intestinal mucosa. Most notably, virus-infected cells are also present among CD11c+ dendritic cells in the subepithelial area of the small intestinal mucosa. Some of these virus-infected cells are in close spatial association with intestinal intraepithelial lymphocytes (IEL). Therefore, we compared virus-specific cytotoxic activity of CD8 splenocytes with that of IEL subsets. While ex vivo isolated TCRalphabeta+CD8alphaalpha+ IEL exert only minimal virus-specific cytotoxicity, maximum specific killing mediated by TCRalphabeta+CD8alphabeta+ IEL on day 8 postinfection exceeds maximum cytotoxic activity observed with CD8 splenocytes when assessed in vitro. Maximum cytotoxic activity of IEL is preceded by peak perforin and granzyme B mRNA expression in IEL around day 6 postinfection, suggesting a recent activation in situ. The antivirus cytotoxicity of in vivo primed IEL is further demonstrated by the protection from virus production in the spleen of mice infected with LCMV 10 h before adoptive cell transfer. These data indicate a potent priming of LCMV-specific IEL in situ after systemic LCMV infection and suggest that cytotoxic IEL markedly contribute to the elimination of virus-infected cells in the intestinal mucosa.