Function Of Intraepithelial Lymphocytes Research Articles

Type I IFN Induces TCR-dependent and -independent Antimicrobial Responses in γδ Intraepithelial Lymphocytes.

Intraepithelial lymphocytes (IELs) expressing the TCRγδ survey the intestinal epithelium to limit the invasion of microbial pathogens. The production of type I IFN is a central component of an antiviral immune response, yet how these proinflammatory cytokines contribute to γδ IEL effector function remains unclear. Based on the unique activation status of IELs and their ability to bridge innate and adaptive immunity, we investigated the extent to which type I IFN signaling modulates γδ IEL function. Using an ex vivo culture model, we find that type I IFN alone is unable to drive IFN-γ production, yet low-level TCR activation synergizes with type I IFN to induce IFN-γ production in murine γδ IELs. Further investigation into the underlying molecular mechanisms of costimulation revealed that TCRγδ-mediated activation of NFAT and JNK is required for type I IFN to promote IFN-γ expression in a STAT4-dependent manner. Whereas type I IFN rapidly upregulates antiviral gene expression independent of a basal TCRγδ signal, neither tonic TCR triggering nor the presence of a TCR agonist was sufficient to elicit type I IFN-induced IFN-γ production invivo. However, bypassing proximal TCR signaling events synergized with IFNAR/STAT4 activation to induce γδ IEL IFN-γ production. These findings indicate that γδ IELs contribute to host defense in response to type I IFN by mounting a rapid antimicrobial response independent of TCRγδ signaling, and may produce IFN-γ in a TCR-dependent manner under permissive conditions.

Functional intraepithelial lymphocyte changes in inflammatory bowel disease and spondyloarthritis have disease specific correlations with intestinal microbiota

BackgroundDysbiosis occurs in spondyloarthritis (SpA) and inflammatory bowel disease (IBD), which is subdivided into Crohn’s disease (CD) and ulcerative colitis (UC). The immunologic consequences of alterations in microbiota, however, have not been defined. Intraepithelial lymphocytes (IELs) are T cells within the intestinal epithelium that are in close contact with bacteria and are likely to be modulated by changes in microbiota. We examined differences in human gut-associated bacteria and tested correlation with functional changes in IELs in patients with axial SpA (axSpA), CD, or UC, and in controls.MethodsWe conducted a case-control study to evaluate IELs from pinch biopsies of grossly normal colonic tissue from subjects with biopsy-proven CD or UC, axSpA fulfilling Assessment of SpondyloArthritis International Society (ASAS) criteria and from controls during endoscopy. IELs were harvested and characterized by flow cytometry for cell surface markers. Secreted cytokines were measured by ELISA. Microbiome analysis was by 16S rRNA gene sequencing from rectal swabs. Statistical analyses were performed with the Kruskal-Wallis and Spearman’s rank tests.ResultsThe total number of IELs was significantly decreased in subjects with axSpA compared to those with IBD and controls, likely due to a decrease in TCRβ+ IELs. We found strong, significant negative correlation between peripheral lymphocyte count and IEL number. IELs secreted significantly increased IL-1β in patients with UC, significantly increased IL-17A and IFN-γ in patients with CD, and significantly increased TNF-α in patients with CD and axSpA as compared to other cohorts. For each disease subtype, IELs and IEL-produced cytokines were positively and negatively correlated with the relative abundance of multiple bacterial taxa.ConclusionsOur data indicate differences in IEL function among subjects with axSpA, CD, and UC compared to healthy controls. We propose that the observed correlation between altered microbiota and IEL function in these populations are relevant to the pathogenesis of axSpA and IBD, and discuss possible mechanisms.Trial registrationClinicalTrials.gov, NCT02389075. Registered on 17 March 2015.

Intraepithelial lymphocytes

Hoytema van Konijnenburg and Mucida discuss development and function of intraepithelial lymphocytes, which are found within the epithelial layer of mucosal and barrier tissues.

Bacterial Dysbiosis Associates with Functional Intraepithelial Lymphocyte Changes in Inflammatory Bowel Disease and Spondyloarthritis

Abstract Dysbiosis occurs in spondyloarthritis (SpA) and inflammatory bowel disease (IBD), subdivided into Crohn’s Disease (CD) and Ulcerative Colitis (UC). The immunologic consequences of dysbiosis have not been defined. Intraepithelial lymphocytes (IELs) are T cells within the intestinal epithelium that are in close contact with bacteria, and as such, are likely to be modulated by dysbiosis. We correlated IELs with resident bacteria in SpA, IBD, and controls. Subjects with biopsy-proven IBD (N=10 with CD and 7 with UC), SpA fulfilling ASAS criteria (N=5), and healthy controls (N=15) were evaluated for fecal microbiome by 16S rRNA sequencing and IELs from colon biopsies analyzed by flow cytometry and ELSIA. Subjects with SpA had significantly lower numbers of IELs compared to controls (p=0.03). Subjects with CD had significantly increased IL-17A, (p=0.03) and IFN-γ (p<0.01) whereas those with UC had higher IL-1β (p=0.01) compared to controls. Both subjects with CD and SpA had significantly increased secretion of TNF-α (p=0.04). Correlating cytokines to bacteria revealed an association between TNF-α and the Simpson Diversity Index in subjects with UC (Spearman’s r=0.943, p<0.01); in subjects with CD, Fusobacterium had a negative correlation with TNFα+IFNγ+IL-1β (Spearman’s r=−0.786, p=0.02). Sequencing results from subjects with SpA are pending. Our data indicate differences in IEL function among subjects with SpA, CD, and UC compared to healthy controls. We hypothesize that the correlations between dysbiosis and IEL function are relevant to the pathogenesis of SpA and IBD. Future studies will be aimed at further understanding mucosal T cell and microbial interactions and may offer new therapeutic targets in these diseases.

A 3-D enteroid-based model to study T-cell and epithelial cell interaction

The constant interaction between intestinal epithelial cells (IECs) and intraepithelial lymphocytes (IELs) is thought to regulate mucosal barrier function and immune responses against invading pathogens. IELs represent a heterogeneous population of mostly activated and antigen-experienced T cells, but the biological function of IELs and their relationship with IECs is still poorly understood. Here, we describe a method to study T-cell–epithelial cell interactions using a recently established long-term intestinal “enteroid” culture system. This system allowed the study of peripheral T cell survival, proliferation, differentiation and behavior during long-term co-cultures with crypt-derived 3-D enteroids. Peripheral T cells activated in the presence of enteroids acquire several features of IELs, including morphology, membrane markers and movement in the epithelial layer. This co-culture system may facilitate the investigation of complex interactions between intestinal epithelial cells and immune cells, particularly allowing long term-cultures and studies targeting specific pathways in IEC or immune cell compartments.

The Transcription Factor T-bet Is Induced by IL-15 and Thymic Agonist Selection and Controls CD8αα+ Intraepithelial Lymphocyte Development

CD8αα(+) intraepithelial lymphocytes (IELs) are instrumental in maintaining the epithelial barrier in the intestine. Similar to natural killer cells and other innate lymphoid cells, CD8αα(+) IELs constitutively express the T-box transcription factor T-bet. However, the precise role of T-bet for the differentiation or function of IELs is unknown. Here we show that mice genetically deficient for T-bet lacked both TCRαβ(+) and TCRγδ(+) CD8αα(+) IELs and thus are more susceptible to chemically induced colitis. Although T-bet was induced in thymic IEL precursors (IELPs) as a result of agonist selection and interleukin-15 (IL-15) receptor signaling, it was dispensable for the generation of IELPs. Subsequently, T-bet was required for theIL-15-dependent activation, differentiation, and expansion of IELPs in the periphery. Our study reveals a function of T-bet as a central transcriptional regulator linking agonist selection and IL-15 signaling with the emergence of CD8αα(+) IELs.

Activation of intra-epithelial lymphocytes; their morphology, marker expression and ultimate fate

Intraepithelial lymphocytes (IELs) have been considered to play a key role in the defense system of the small intestine. Its mechanism has not been made sufficiently clear. Studies on IELs have been extremely limited to functions of αβ T-cell receptor (αβTCR) IELs (αβ-IELs). Since, in the mouse duodenum and jejunum, γδ-IELs consist 75 % of IELs, it thus would be inappropriate to argue the mechanism without extensive discussions over the functions of γδ-IELs. In previous studies, we found that the anti-CD3 monoclonal antibody (mAb) injection induced DNA fragmentation in intestinal epithelial cells (IECs) and DNA repair immediately after, that these responses were reproduced by anti-γδTCR mAb not by anti-αβTCR mAb and that the DNA fragmentation was induced by Granzyme B secreted by IELs, totally independent of Perforin. To further explore the functions of IELs in situ, we undertook experiments exclusively focused on IELs, on their changes and ultimate fate after the stimulation in mouse in vivo system. The current study demonstrated that the injected anti-CD3 mAb bound to CD3 on IELs, that the mAb activated γδ-IELs, leading to their degranulation, that changes occurred irreversibly in IELs and finally that activated IELs died in situ. γδ-IELs could be considered to respond to various stimulations most likely without the need of accessory cells ("always ready for rapid response"), to die in situ ("disposable") and thus to respond to the stimulation only once ("a one-shot responder"). These characteristics of γδ-IELs are important to further elucidate the functions of γδ-IELs in the intestinal defense system.

Effects of Intraepithelial Lymphocyte-Derived Cytokines on Intestinal Mucosal Barrier Function

The mucosal surface of the gastrointestinal tract directly interacts with the mucosal lumen, which is continuously exposed to foreign antigens. Specialized intraepithelial lymphocytes (IELs), located between the basolateral surfaces of the epithelial cells, are important as the first line of defense against microbes as well as for their role in the maintenance of epithelial barrier homeostasis. Although IELs are mainly composed of T cells, they are phenotypically and functionally distinct from T cells in peripheral blood or the spleen. Not only are IELs stimulated by the antigens of the intestinal lumen but are they also stimulated by regulatory immune cells. The integrity of the intestinal mucosal barrier is closely tied to the IEL function. Cytokines produced by IELs modulate the cellular functions that trigger the downstream signaling pathways and mediate the barrier homeostasis. In this review, we will address the broad spectrum of cytokines that are derived from IELs and the functional regulation of these cytokines on the intestinal barrier.

Phenotypical and Functional Analysis of Intraepithelial Lymphocytes from Small Intestine of Mice in Oral Tolerance

In this work, we evaluated the effects of administration of OVA on phenotype and function of intraepithelial lymphocytes (IELs) from small intestine of transgenic (TGN) DO11.10 and wild-type BALB/c mice. While the small intestines from BALB/c presented a well preserved structure, those from TGN showed an inflamed aspect. The ingestion of OVA induced a reduction in the number of IELs in small intestines of TGN, but it did not change the frequencies of CD8+ and CD4+ T-cell subsets. Administration of OVA via oral + ip increased the frequency of CD103+ cells in CD4+ T-cell subset in IELs of both BALB/c and TGN mice and elevated its expression in CD8β + T-cell subset in IELs of TGN. The frequency of Foxp3+ cells increased in all subsets in IELs of BALB/c treated with OVA; in IELs of TGN, it increased only in CD25+ subset. IELs from BALB/c tolerant mice had lower expression of all cytokines studied, whereas those from TGN showed high expression of inflammatory cytokines, especially of IFN-γ, TGF-β, and TNF-α. Overall, our results suggest that the inability of TGN to become tolerant may be related to disorganization and altered proportions of inflammatory/regulatory T cells in its intestinal mucosa.

The thymus leukemia antigen controls intraepithelial lymphocyte function and inflammatory bowel disease (39.53)

Abstract Intestinal intraepithelial lymphocytes (IEL) bear a partially activated phenotype that permits them to rapidly respond to antigenic insults. However, this phenotype also implies that IEL must be highly controlled to prevent misdirected immune reactions. It has been suggested that IEL are regulated through the interaction of the CD8alpha-alpha homodimer with the thymus leukemia (TL) antigen expressed by intestinal epithelial cells. We have generated and characterized mice genetically deficient in TL expression. Our findings show that TL expression plays a critical role in maintaining IEL effector functions. Moreover, TL deficiency accelerated colitis in a genetic model of inflammatory bowel disease. These findings reveal an important regulatory role of TL in controlling IEL function and intestinal inflammation.

CD100 modulation of intraepithelial lymphocyte function during colitis

To investigate the role of a potential costimulatory molecule, CD100, on intraepithelial lymphocytes (IEL) function during murine colitis. During the disease course of colitis, IEL bearing the γδ T-cell receptor become activated and secrete cytokines and growth factors including keratinocyte growth factor (KGF) that are important in repair of epithelial damage and down regulation of inflammation. Little is known about moleculesthat regulate γδ IEL function. Our lab has identified CD100 as a potential costimulatory molecule that can impact the activation of γδ T-cells in vitro. We investigated the role of CD100 on IEL function during colitis by administering dextran sulfate sodium (DSS) to CD100 null mice. Both αβ and γδIELs were found to express CD100, while enterocytes expressed a ligand to CD100, Plexin-B2. Upon DSS administration, colitis severity was found to be significantly worse in CD100 null mice as compared to wildtype mice, with increased weight loss, higher histological disease score, and increased length of lesions. The severe disease of the CD100 null mice was partly attributable to the failure of the colon epithelium and the resident IEL to increase proliferation in response to colitis. γδ IEL are known to mediate epithelial proliferation by expressing the potent mitogen KGF. γδ IEL from wild-type mice treated with DSS significantly increased their expression of KGF mRNA while γδ IEL from CD100 null mice failed to do so. In conclusion, CD100 and Plexin-B2 appearto be important in epithelial recovery from colitis by enhancing the function of γδ IEL. Supported by NIH grants A152257 and A107244-23 and a fellowship from the Crohn's and Colitis Foundation

CD100 modulation of intraepithelial lymphocyte function during colitis

CD100 modulation of intraepithelial lymphocyte function during colitis

Lack of enteral nutrition—effects on the intestinal immune system

Total parenteral nutrition (TPN) results in a loss of mucosal immune function by alterations in both phenotype and function of intraepithelial lymphocytes (IEL). We hypothesized that the observed changes with TPN administration are caused by the lack of enteral feeding, and not to the TPN solution itself. Mice received oral feeding (Control), TPN alone (TPN), or TPN plus oral feeding (TPN+Food). Mice were killed after 7 days, and bacteriological cultures from spleen, liver, and mesenteric lymph nodes obtained, with bacterial translocation (BT) being defined as a positive culture. IEL phenotype was analyzed by flow cytometry. IEL messenger RNA (mRNA) cytokine expression used reverse transcriptase polymerase chain reaction (RT-PCR). Apoptosis was detected by terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining. BT significantly (P < 0.05, with analysis of variance [ANOVA]) increased in the TPN group (53%) compared with Control (9%) and TPN+Food (14%) groups. TPN also resulted in a significant (P < 0.01) increase in epithelial cell apoptosis: TPN 7.6 +/- 1.1% versus Control 2.9 +/- 1.1% and TPN+Food 2.1 +/- 0.3% (mean +/- SD). Height of the villus-crypt complex was significantly decreased in TPN mice (315 +/- 16 microm) compared with Control (431 +/- 27 microm) and TPN+Food (421 +/- 26 microm) groups. IEL phenotypes significantly changed with TPN administration: CD4+ CD8- as well as CD4+ CD8+ subpopulations were reduced compared with Control or TPN+Food mice; as were the CD8alphabeta+ thymus-dependent, and CD8+ CD44+ mature IEL. IEL cytokine mRNA expression was also significantly altered with TPN: IL-2 and IL-10 expression declined, and IL-4 IL-6, interferon gamma (IFN-gamma), transforming growth factor beta-1 (TGF-beta1), and tumor necrosis factor-alpha (TNF-alpha) were increased, when compared with Control or TPN+Food mice. This study demonstrates that the major factor responsible for TPN-induced BT and IEL-changes is the lack of enteral feeding and not the administration of the TPN solution itself.

Exposure to fatty acids modulates interferon production by intraepithelial lymphocytes

Intraepithelial lymphocytes (IELs) play important roles in intestinal mucosal immunity. Although fatty acids are known to modulate the functions of immune effector cells, there has been no information about how fat exposure affects immunological function of IELs. In this study, we examined how fatty acids of various chain lengths modulate the production of interferon (IFN)-γ by IELs stimulated with T-cell receptor (TCR) or interleukin (IL)-12/IL-18. IELs isolated from the small intestine of BALB/c mice were stimulated with plate-coated anti-CD3 monoclonal antibody (mAb) or IL-12/IL-18. They were coincubated in microtiter plates for 3 days with various concentrations of fatty acid micelles. We used arachidonic acid, linoleic acid, and oleic acid as long-chain fatty acids, and used octanoic acid as a medium-chain fatty acid. IFN-γ in the supernatants were measured by ELISA, and the expression of IFN-γ mRNA in IELs was determined by RT-PCR. Significant production of IFN-γ from IELs was observed after anti-CD3 mAb stimulation. The combination of IL-12 and IL-18 induced significant levels of IFN-γ production without TCR stimulation. Increased IFN-γ mRNA was also observed after anti-CD3 or IL-12/IL-18 stimulation. Long-chain fatty acids dose-dependently inhibited the stimulated-IFN-γ production at concentrations greater than 10 μM, but the medium-chain fatty acid did not cause any significant changes in IFN-γ production. IFN-γ production from γδ IELs was very low compared with αβ IELs, however, both populations showed similar attenuating patterns when treated with long-chain fatty acids. There is a possibility that the exposure of IELs to intraluminal fatty acids significantly modifies the immune function of intestinal mucosa.

Inhibitory effects of transforming growth factor-beta (TGF-beta) on certain functions of intraepithelial lymphocytes.

Human intraepithelial lymphocytes (IEL), CD8+ lymphocytes located between epithelial cells, are likely to be influenced by the immunosuppressive cytokine, TGF-beta, secreted by epithelial cells. This study evaluates the effects of TGF-beta on IEL functions. IEL were derived from proximal jejunum of patients undergoing gastric bypass operations for morbid obesity. Proliferation was determined by 3H-thymidine incorporation; IL-2 production, by ELISA; expression of IL-2 receptor, CD2, HML1, CD16, and CD56, by immunofluorescence; binding, by adherence of radiolabelled cells; and cytotoxicity by 51Cr-release assay. TGF-beta (> or = 1 ng/ml) inhibited the mitosis of IEL to mitogens, IL-7, and stimuli of the CD2 and CD3 pathways. The blocking effect did not target the activation events of IL-2 production and receptor generation. Rather, it reduced cell division after activation when added 24 h after initiating the culture. Antibody neutralization of naturally occurring TGF-beta increased IEL proliferation to IL-2, but not to the other stimuli. Of the multiple surface markers tested, only CD2 and HML1 expression increased with TGF-beta and decreased with antibody to TGF-beta, although the cytokine and the neutralizing antibody had no effects on IEL binding to colon cancer. TGF-beta reduced the number of CD56+ IEL and the lymphokine-activated killing when co-cultured with IL-7 but not with IL-2 or IL-15. TGF-beta inhibits certain IEL functions: the reduction in cell division rather than activation and a decline in IL-7-mediated lysis of colon cancer due to a lowering of the number of natural killer cells.

Intestinal T cells in CD8 alpha knockout mice and T cell receptor transgenic mice.

Intraepithelial lymphocytes (IEL) refer to the T cells located at the epithelium of the intestines. Unlike the T cells in other peripheral lymphoid organs, the majority of IEL express the CD8 cell surface protein. To study the role of CD8 in the ontogeny and the function of IEL, phenotypic analysis of IEL from CD8 alpha knockout mice and normal mice was performed. The CD8 alpha gene in CD8 alpha knockout mice was disrupted by homologous recombination. These mice are defective in thymic maturation of cytotoxic T cells. In normal mice, alpha beta T cells that were CD8 alpha alpha+ or CD4+ CD8 alpha alpha+, and gamma delta T cells that were CD8 alpha alpha+, were the distinct populations found only in IEL. In CD8 alpha knockout mice, the population size of IEL remained normal, but the majority of IEL were CD4- CD8- T cells expressing alpha beta or gamma delta T cell receptors. IEL from the H-Y transgenic mice2, which express the male H-Y antigen specific T cell receptor in a normal and in a CD8 alpha-null background, were also studied. In contrast to thymic derived T cells, CD8 alpha alpha+ IEL with the autoreactive transgenic T cell receptor were not deleted, but clonally expanded in the male transgenic mice. Interestingly, no pathological symptoms were observed in the intestines of these mice. In the absence of CD8 alpha expression, the H-Y specific autoreactive IEL did not accumulate in the intestines. The results suggest that CD8 alpha alpha+ IEL are derived extra-thymically and their responses towards antigens require the CD8 accessory molecule.

Novel function for intestinal intraepithelial lymphocytes. Murine CD3+, gamma/delta TCR+ T cells produce IFN-gamma and IL-5.

Intestinal intraepithelial lymphocytes (IEL) from mice are greater than 80% CD3+ T cells and could be separated into four subsets according to expression of CD4 and CD8. In our studies designed to assess the functions of IEL, namely, cytokine production, it was important to initially characterize the various subsets of T cells that reside in IEL. The major subset was CD4-, CD8+ (75% of CD3+ T cells), which contained approximately 45 to 65% gamma/delta TCR+ and 35 to 45% alpha/beta TCR+ T cells. Approximately 7.5% of IEL T cells were CD4-, CD8- (double negative) and gamma/delta+ population. On the other hand, CD4+, CD8+ (double positive) and CD4+, CD8- fractions represented 10% and 7.5% of CD3+ T cells, respectively, which were all alpha/beta TCR+. Inasmuch as CD3+, CD4-, CD8+ T cells are a major subset of IEL which contain both gamma/delta TCR or alpha/beta TCR-bearing cells, the present study was focused on the capability of this subset of IEL T cells to produce the cytokines IFN-gamma and IL-5. Both gamma/delta TCR+ and alpha/beta TCR+ IEL spontaneously produced IFN-gamma and IL-5, although higher frequencies of cytokine spot-forming cells were associated with the alpha/beta TCR+ subset. Approximately 30% of CD8+, gamma/delta TCR+ cells produced both cytokines, whereas approximately 90% of alpha/beta TCR+ T cells produced either IFN-gamma or IL-5. Both gamma/delta TCR+ and alpha/beta TCR+ IEL possessed large quantities of cytokine-specific mRNA, clearly showing that these IEL were programmed for cytokine production. When IEL were activated with anti-gamma/delta or anti-CD8 antibodies, higher numbers of IFN-gamma and IL-5 spot-forming cells were noted. The present study has provided direct evidence that a major function of IEL involves cytokine production, and this is the first evidence that gamma/delta TCR+ cells in IEL possess the capability of producing both IL-5 and IFN-gamma.

Intraepithelial lymphocytes. Anatomical site, not T cell receptor form, dictates phenotype and function.

The function and structure of the TCR proteins of intraepithelial lymphocytes (IEL) were examined using a panel of mAbs specific for TCR-gamma/delta. Three subsets of TCR-gamma/delta+ IEL could be detected with five mAbs, termed GL1-GL5. The mAbs were able to trigger lysis via crosslinking of the IEL TCR and all of the subsets were constitutively cytolytic. Immunoprecipitation of IEL TCR proteins revealed that the GL2 mAb reacted only with gamma, delta heterodimers containing high Mr delta chains, while the other mAbs precipitated all of the observed gamma and delta proteins. Two-color fluorescence analysis showed that the GL2+ subset was contained within the larger GL1+ subset. The GL3 and GL4 mAbs appear to be specific for all TCR-gamma/delta while GL2 was V delta 4 specific. Analysis of IEL for TCR-alpha/beta expression demonstrated that approximately 20% of B6 IEL were TCR-alpha/beta+. Interestingly, this population of IEL contained Thy-1- and CT1+ cells, indicating that the unique phenotype of IEL was not restricted to TCR-gamma/delta+ cells. Moreover, the TCR-alpha/beta+ IEL were also constitutively cytolytic, suggesting that the intestinal milieu was controlling the functional programming of IEL regardless of TCR type. The mAbs reported here as well as the ability to exploit the distinct phenotype of IEL should prove useful in determining the function of IEL and the TCR-gamma/delta.

Spontaneous in vitro evolution of lytic specificity of cytotoxic T lymphocyte clones isolated from murine intestinal epithelium.

Three long-term clonally derived cytotoxic lines have been established from isolates of murine intraepithelial lymphocytes (IEL). All three lines were selected for with antigen and represent two allospecific cytotoxic T lymphocyte (CTL) clones and a major histocompatibility complex (MHC)-restricted clone specific for a murine minor histocompatibility antigen. On long-term in vitro culture, IEL clones gradually lost antigen-specific lytic activity and simultaneously acquired the capacity to lyse natural killer (NK)-sensitive target cells which, in some cases, required high-level lymphokine activation. Of interest was the finding that, despite changes in lytic specificity, IEL clones remained strictly antigen-dependent for proliferation. A murine CTL clone of splenic origin, which was propagated under culture conditions identical to those used for IEL, did not exhibit changes in lytic specificity, suggesting that acquired changes in IEL function cannot be attributed solely to the influence of in vitro culture. Phenotypic analyses of IEL clones with altered lytic specificity revealed that all lines remained Thy-1+, Lyt-2+, L3T4-, with or without lytic activation by lymphokines. The expression of CT-1, a murine CTL activation antigen, and asialo GM1, a murine NK cell marker, were variable on IEL clones, and their presence did not correlate with the changes in lytic behavior. Collectively, these findings provide evidence, at the clonal level, that at least some NK activity present in isolates of murine IEL may originate from antigen-specific CTL. The data also indicate that, on binding antigen, different signals are conveyed to T cells, resulting in proliferation or target cell lysis.

Immunohistological characterisation of intraepithelial lymphocytes of the human gastrointestinal tract.

Intraepithelial lymphocytes (IEL) of the normal human stomach, small intestine, and large intestine have been characterised in tissue sections by a double marker immunofluorescent technique. A panel of reagents was used in combination, including antisera to T lymphocyte antigen (HuTLA), Ia-like (p28, 33) antigens and immunoglobulin subclasses, as well as a mouse monoclonal antibody to a human leucocyte antigen (HLe-1). In stomach and proximal small intestine over 95% of IEL were T lymphocytes (HLe-1+, HuTLA+). The proportion was slightly lower in the colon and rectum (85--95%). IEL rarely expressed Ia-like antigens. B lymphocytes were not seen within the epithelium of any of the tissues examined. The functions of IEL must be assessed in the light of the finding that they are predominantly T cells.