Murine Intestinal Intraepithelial Lymphocytes Research Articles

Rapid killing of murine lymph node T blasts by intestinal intraepithelial lymphocytes in vitro.

We examined the effect of murine intestinal intraepithelial lymphocytes (IEL) on the proliferation of murine lymph node T cells (LN-T) in vitro. An IEL fraction prevented the proliferation of LN-T stimulated with antigen and X-irradiated spleen cells, or with anti-CD3 monoclonal antibodies (mAb). Concanavalin A-activated LN-T were less sensitive. Such an inhibitory activity was recovered from a CD8-depleted population by panning of bulk IEL using anti-CD8 alpha mAb. This population of BALB/c IEL showed less granzyme A activity, and its surface markers were positive for CD8 (4%), CD3 (80-90%), CD4 (2-6%), alpha-beta TcR (45-70%), and gamma-delta TcR (4-9%). Asialo-GM1 and Thy1.2 were variably expressed, but interleukin-2 (IL-2) receptor-alpha and Fc gamma receptor were not. By contrast, no cytotoxicity against YAC-1 was detected in a CD8-depleted IEL population by a 6-h 51Cr-release assay. Although IEL from severe-combined immunodeficient mice lacking CD4, CD8 and TcR, but expressing IL-2 receptor, showed cytotoxicity against YAC-1, their inhibitory activity against LN-T was almost the same as that by IEL from BALB/c mice. When LN-T blasts (greater than 75% CD4+) activated with anti-CD3 were treated with CD8-depleted IEL, intact cellular DNA of the T blasts disappeared within 1 h with increased amounts of small-sized DNA. These results suggest that CD8- IEL directly and nonspecifically kill lymph node CD4+ T blasts and possibly down-regulate TcR-mediated proliferation of peripheral T cells in the gut epithelium.

Evidence against T-cell development in the adult human intestinal mucosa based upon lack of terminal deoxynucleotidyltransferase expression.

Several lines of evidence indicate that a subset of murine intestinal intraepithelial lymphocytes (iIEL), particularly those which express the CD8 alpha alpha homodimer, mature extrathymically. This study confirms that a small fraction of adult human iIEL also express the CD8 alpha alpha homodimer and demonstrates that most of these cells in the small intestine are T cells using the alpha beta T-cell receptor (TCR). Whether these cells or other subsets of adult human iIEL mature extrathymically in the intestine was assessed by measuring the expression of terminal deoxynucleotidyltransferase (TdT), an enzyme expressed exclusively by immature lymphocytes. Very low levels of TdT message could be detected by polymerase chain reaction (PCR) amplification in some iIEL samples. The level of TdT expression was assayed by competitive PCR amplification and compared with thymocytes and peripheral blood lymphocytes. These measurements indicated that the number of immature T cells expressing TdT in the intestinal epithelium was less than one cell per 10(7) lymphocytes. This demonstrates that there are few if any TdT expressing immature T cells in the adult human intestinal mucosa and indicates, therefore, that T-cell development in the intestinal mucosa does not contribute significantly to the T-cell repertoire of the adult human intestine.

Activated alpha beta-CD8+, but not alpha alpha-CD8+, TCR-alpha beta+ murine intestinal intraepithelial lymphocytes can mediate perforin-based cytotoxicity, whereas both subsets are active in Fas-based cytotoxicity.

CD8 single-positive (CD8+) T cells in murine intestinal intraepithelial lymphocytes (iIEL) consist of alpha alpha-CD8+ and alpha beta-CD8+ subpopulations. Cytotoxicity represents an important function of peripheral CD8+ T cells, so we examined perforin-granzymebased and Fas-based cytotoxicity of activated CD8+ TCR-alpha beta+ iIEL subsets. We found that allospecific CTL activity was induced from alpha beta-CD8+ iIEL but not from alpha alpha-CD8+ iIEL even when allospecific TCR were present on the iIEL, as demonstrated by using 2C TCR transgenic mice. On the other hand, both CD8+ iIEL subsets proliferated upon allostimulation with a lower responder frequency than CD8+ LN cells. The alpha alpha-CD8+ TCR-alpha beta+ iIEL appeared to lose their ability to perform perforin-based killing after activation through TCR because fresh cells lysed P815 cells coated with anti-TCR beta-chain (TCR-beta) mAb, whereas cells activated by plate-bound anti-TCR mAb did not. Of interest, both activated CD8+ TCR-alpha beta+ iIEL subsets, but not fresh cells, were able to mediate Fas-based killing when triggered with PMA and CA2+ ionophore.

Dynamic regulation of intestinal immunity by hormones of the hypothalamus-pituitary-thyroid axis

The role of the thymus in the development of murine small intestinal intraepithelial lymphocytes (IELs) has been a controversial topic for decades. This controversy has been further propagated by observations that differences in IEL repertoires vary according to the particular athymic animal model system used to study IELs. In an attempt to understand the bases for these differences, we have undertaken a series of experiments designed to explore the extent to which extraimmunologic events, in particular neuroendocrine factors, play a role in the development of extrathymic IELs. As discussed here, these studies indicate that hormones of the hypothalamus-pituitary-thyroid (HPT) axis exert either positive or negative regulatory effects on intestinal IELs, depending upon the particular hormone. Although the mechanisms by which HPT hormones influence IEL development and immune regulation have yet to be fully delineated, it appears that thyroid-stimulating hormone is a key mediator in this process, and that this may occur via local autocrine/paracrine responses within the intestine itself. The implications of these findings in the context of immunity and disease at the level of the gastrointestinal tract are discussed.

T Cell Repertoire and Inflammatory Bowel Disease

The diversity of the T cell receptor repertoire is generated through rearrangement of the variable, junctional and constant region genes. Selection processes in the thymus and periphery serve to eliminate self-reacting T cells, thereby preventing autoimmune disease. The possibility that inflammatory bowel disease (IBD) is an autoimmune disease has led to the search for an auto-antigen. In addition, studies are exploring the T cell receptor repertoire in IBD patients for changes that may provide clues regarding etiopathogenesis. Using monoclonal antibodies to T cell receptor variable-gene products or polymerase chain reaction analysis of variable-gene mRNA expression, the mucosal T cell repertoire has been examined in humans. The intestinal intraepithelial lymphocytes show a significant degree of oligoclonal expansion that may represent local antigen exposure or unique selection processes. This is in keeping with studies that show that murine intestinal intraepithelial lymphocytes undergo positive and possibly negative selection independent of the thymus. In the inflamed human gut, shifts in the T cell receptor repertoire may also reflect recruitment of peripheral T cells to the gut. In one study, a subset of Crohn’s disease patients was shown to have an increase in the proportion of variable β8 peripheral blood lymphocyte and mesenteric lymph node cells, suggesting a superantigen effect. The authors hypothesized that changes in the functional T cell receptor repertoire can also occur which might be independent of changes in the distribution of T cells expressing variable β T cell receptors. In fact, the authors have shown there is a selective decrease in the cytotoxic function of peripheral variable β8 T cells in Crohn’s disease. Furthermore, stimulation with the variable β8 selective bacterial enterotoxin staphylococcal enterotoxin E failed to increase the cytotoxic function in this subset of Crohn’s disease patients compared with controls. This suggests that in Crohn’s disease, variable β8 T cells have undergone an alteration in function that may reflect previous exposure to a superantigen-like stimulus. The relationship to the etiology and pathogenesis of IBD remains to be defined.

Development of TCR-gamma delta CD4-CD8+ alpha alpha but not TCR-alpha beta CD4-CD8+ alpha alpha i-IEL is resistant to cyclosporin A.

Present evidence suggests that cyclosporin A (CSA) inhibits the development of both alpha beta and gamma delta T cells in the thymus. However, whether CSA can inhibit the development of murine intestinal intraepithelial lymphocytes (i-IEL) is unknown as most i-IEL are clearly derived from a different lineage than the conventional thymus-derived T cells found in the periphery. Using the adult thymectomized, lethally irradiated bone-marrow reconstituted chimera (ATXBM mice) as a model for the development of extrathymically derived i-IEL and the fetal thymus-grafted (FTG) nude mice as a model for the development of thymically derived i-IEL, we demonstrate that CSA nearly completely inhibited the development of extrathymically, and possibly thymically, derived TCR-alpha beta i-IEL. Most of the TCR-alpha beta i-IEL whose development was inhibited by CSA belonged to the CD4-CD8+ alpha alpha subset. In contrast, the development of extrathymically and thymically derived TCR-gamma delta i-IEL was completely resistant to CSA. The phenotype of CSA-resistant TCR-gamma delta i-IEL in these models was not different from those in control mice, and the TCR-gamma delta i-IEL in CSA-treated mice appear to be mature and activated as most were large, granular, and CD69+. Lastly, we demonstrate that CSA does not affect the extrathymic positive selection of V delta 4 i-IEL in C3H hosts. These results suggest that despite their similarity, the intracellular activation cascade involved after TCR stimulation between TCR-alpha beta CD4-CD8+ alpha alpha and TCR-gamma delta CD4-CD8+ alpha alpha i-IEL are markedly different.

Extrathymic and thymic origin of murine IEL: Are most IEL in euthymic mice derived from the thymus?

Although an abundance of literature supports the hypothesis that murine intestinal intraepithelial lymphocytes (IEL) can develop extrathymically, whether most IEL in euthymic mice ar extrathymically derived is unknown. Recent evidence, however, suggests that the development of most IEL in euthymic mice is influenced either directly or indirectly by the thymus. While some evidence suggests that the thymus can influence the extrathymic development of IEL through time-derived factors, clearly a substantial portion (if not most) of the IEL in euthymic mice are derived directly from the thymus. The ability of the thymus to generate IEL depends on the age of the thymus, as fetal/neonatal thymus up to approximately 2 weeks of age generates a totally different subset of IEL than the adult thymus. These results suggest that the IEL generated from the fetal early neonatal thymus recognize a different antigen than the IEL generated from the adult thymus. The former probably recognizes self-antigen and the later recognizes bacterial antigen.

Control of thymus-independent intestinal intraepithelial lymphocytes by beta 2-microglobulin.

Murine intestinal intraepithelial lymphocytes (i-IEL) comprise thymus-dependent cells such as T cell receptor (TcR) alpha/beta CD8 alpha/beta+ i-IEL, as well as thymus-independent ones such as TcR alpha/beta CD8 alpha/alpha+ and TcR gamma/delta CD8 alpha/alpha+ i-IEL. Whilst the development of the CD8 alpha/beta expressing i-IEL is strictly contingent on major histocompatibility complex (MHC) class I surface expression, that of CD8 alpha/alpha i-IEL appears largely MHC class I independent. We have used beta 2-microglobulin (beta 2m)-/- mutant mice lacking surface-expressed MHC class I and TcR alpha/beta CD8 alpha/beta+ i-IEL to analyze the potential impact of MHC class I on regional activation of thymus-independent i-IEL. To analyze the role of TcR gamma/delta i-IEL in regional cell interactions, these mice were treated with the anti-TcR gamma/delta mAb, GL3. Whilst numbers of TcR alpha/beta CD8 alpha/alpha i-IEL were markedly reduced in beta 2m-/- mice, those of TcR gamma/delta i-IEL were elevated. Administration of GL3 in vivo caused TcR down-modulation and functional inactivation of TcR gamma/delta i-IEL in beta 2m+/- mice. In contrast, TcR expression and functional activities of TcR gamma/delta i-IEL from beta 2m-/- mice were not impaired by GL3 treatment. The TcR alpha/beta CD8 beta- i-IEL from beta 2m-/- mice were expanded and functionally activated as a consequence of TcR gamma/delta engagement. The TcR gamma/delta i-IEL and TcR alpha/beta CD8 alpha/alpha+ i-IEL from athymic nu/nu mice which express MHC class I, but lack TcR alpha/beta CD8 alpha/beta+ i-IEL, responded to TcR gamma/delta engagement as those from the beta 2m+/- controls. In addition, the TcR gamma/delta i-IEL from TcR beta-/- and TCR beta+/- mutants were equally affected by GL3. We conclude that the absence of beta 2m renders TcR gamma/delta i-IEL resistant to TcR-mediated inactivation and promotes activation of TcR alpha/beta CD8 beta- i-IEL. The activation of TcR gamma/delta i-IEL seems to be directly controlled by beta 2m/MHC class I expression and independent from TcR alpha/beta CD8 beta+ i-IEL. Regulation of self-reactive thymus-independent i-IEL through beta 2m/ MHC class I may contribute to control of autoreactive immune responses in the intestine.

Differential requirement of CD28 costimulation for activation of murine CD8+ intestinal intraepithelial lymphocyte subsets and lymph node cells.

The CD8+CD4- (CD8+) murine small intestinal intraepithelial lymphocytes (IELs) contain two subpopulations, one expressing alpha alpha-CD8 homodimers and another alpha beta-CD8 heterodimers. In this study, plate-bound anti-TCR beta-chain (TCR-beta) mAb alone or combined with anti-CD28 mAb is used as a model system to study activation requirement of these two CD8+ IEL subsets. In contrast to CD8+ lymph node (LN) cells that require both TCR and CD28 triggering for activation, alpha beta-CD8+ IELs proliferate and produce IL-2 and IFN-gamma when stimulated with anti-TCR-beta mAb alone, and soluble CTLA-4 Ig has no effect on their responses. On the other hand, alpha alpha-CD8+ IELs neither make IL-2 or IFN-gamma nor proliferate even when both stimuli are provided. However, alpha alpha-CD8+ IELs are capable of proliferation in both CD8+ IEL subsets is lower than in CD8+ LN cells, which contributes to the weaker and delayed response of CD8+ IELs.

Activation-induced apoptosis in murine intestinal intraepithelial lymphocytes in vivo: [formula omitted], and D. Maric. Dept of Medicine, Intestinal Disease Research Unit, McMaster University, Hamilton, Ontario

Activation-induced apoptosis in murine intestinal intraepithelial lymphocytes in vivo: [formula omitted], and D. Maric. Dept of Medicine, Intestinal Disease Research Unit, McMaster University, Hamilton, Ontario

Effect of neonatal thymectomy on murine small intestinal intraepithelial lymphocytes expressing T cell receptor alpha beta and "clonally forbidden V beta s".

Neonatal thymectomy NTX performed on Day 3 of C3H mice causes over a 50% reduction in small intestinal intraepithelial lymphocytes (IEL) expressing the alpha beta T cell receptor (TCR) when analyzed at 10 weeks of age. Furthermore, this reduction is most notable in alpha beta TCR IEL expressing the CD8 alpha homodimer and no Thy 1 marker. This is in direct contradiction to the present theory that alpha beta TCR IEL expressing these markers are thymic independent. Evaluation of V beta expression shows a relative increase in V beta s which are clonally forbidden (V beta s 3, 5, 11), and which is consistent with the extrathymic origin of these particular IEL.

Heat-Stable Antigen May Be an Early Marker of Extrathymic Murine Intestinal Intraepithelial Lymphocytes

Using a system of bone marrow (BM) hematopoietic repopulation of irradiated euthymic and athymic mice, we have examined the early stages of extrathymic T-cell development within the murine small intestine epithelium. During a period of active extrathymic T-cell development, two distinct populations of intraepithelial lymphocytes (IEL) were present. One consisted of CD3+ lymphocytes with phenotypic properties of mature IEL. The other population consisted of a transient IEL subset that increased in abundance between days 5 and 14 post-BM transfer, and then declined. The majority of transient IEL in both types of mice expressed the heat-stable antigen, of which some cells coexpressed CD3 but were void of other markers common to mature T cells. Studies using freshly extracted IEL from normal nonirradiated mice found that approximately 3% to 5% of the IEL had phenotypic properties similar to the transient IEL observed during repopulation of radiation chimeras, indicating that such IEL are present within the gut epithelium of normal, nonirradiated mice. Identification of this IEL subset should greatly facilitate studies of extrathymic IEL development.

Heat-stable antigen may be an early marker of extrathymic murine intestinal intraepithelial lymphocytes

Using a system of bone marrow (BM) hematopoietic repopulation of irradiated euthymic and athymic mice, we have examined the early stages of extrathymic T-cell development within the murine small intestine epithelium. During a period of active extrathymic T-cell development, two distinct populations of intraepithelial lymphocytes (IEL) were present. One consisted of CD3+ lymphocytes with phenotypic properties of mature IEL. The other population consisted of a transient IEL subset that increased in abundance between days 5 and 14 post-BM transfer, and then declined. The majority of transient IEL in both types of mice expressed the heat-stable antigen, of which some cells coexpressed CD3 but were void of other markers common to mature T cells. Studies using freshly extracted IEL from normal nonirradiated mice found that approximately 3% to 5% of the IEL had phenotypic properties similar to the transient IEL observed during repopulation of radiation chimeras, indicating that such IEL are present within the gut epithelium of normal, nonirradiated mice. Identification of this IEL subset should greatly facilitate studies of extrathymic IEL development.

Thymus-Neuroendocrine Interactions in Extrathymic T Cell Development

Studies of the development of murine intestinal intraepithelial lymphocytes (IELs) have yielded markedly different results depending on the experimental system used. In athymic radiation chimeras, IELs consist of all subsets found in euthymic mice; adult mice that were athymic at birth have only IELs that are positive for T cell receptor gamma delta and CD8 alpha alpha. These differences are resolved by the finding that administration of the neuropeptide thyrotropin-releasing hormone to adult mice thymectomized as neonates leads to the development of all IEL T cells. Thus, a neuroendocrine signal initiated by the thymus during fetal or neonatal life appears to be required for subsequent extrathymic maturation of gut alpha beta T cells.

Functional heterogeneity of murine intestinal intraepithelial lymphocytes: studies using TCR-αβ + IEL lines and fresh iel isolates reveal multiple cytotoxic subsets differentiated by CD5, CD8α/α, and CD8α/β expression

Three T-cell lines, isolated from murine small intestine epithelia, have been studied with respect to phenotypic properties and cytotoxic activity. All lines were TCR-αβ +, Thy-1 +, CD3 +, CD4 −, CD 8+ but differed in that one line was CD8α/α +, CD5 −; one line was CD8α/α +, CD5 +; and one line was CD8α/β +, CD5 +. Both the CD8α/α +, CD5 −, and the CD8α/β +, CD5 + lines lysed antigen-bearing target cells; however, the latter line also spontaneously lysed natural killer (NK)-sensitive target cells. The CD8α/α +, CD5 + IEL line was nonlytic for antigen-bearing target cells, for NK-sensitive target cells, and in assays that detect lytic activity regardless of specificity. Three-color flow cytometric analyses of intestinal intraepithelial lymphocytes (IEL) in freshly-extracted preparations indicated that cells with the phenotypes of the three IEL lines are normally present in the murine intestine epithelium, and revealed considerable variability in the distribution and density of CD5 expression on murine IEL. In freshly extracted IEL depleted of CD5 or CD8β by cell sorting, cytotoxicity was found to reside both within the CD5 + and the CD5 − IEL subsets, as well as in the CD8β-depleted (i.e., CD8α/α +) subset. These findings demonstrate: that cytotoxicity of murine IEL resides among multiple phenotypic subsets; that the distribution and density of CD5 on IEL is more complex than previously described; and that T-cell lines of IEL origin are valuable for dissecting functional properties of specific IEL subsets, particularly those that constitute a small proportion of the total IEL.

Phenotype and TCR gamma delta variable gene repertoire of intestinal intraepithelial lymphocytes in wild mice (Mus musculus domesticus): abundance of V gamma 1 transcripts and extensive delta gene diversity.

In order to study murine intestinal intraepithelial lymphocytes (IEL) independent of factors imparted by conditions of laboratory housing and breeding, and to provide a basis for comparison of IEL studies between inbred and outbred mouse populations, IEL from the domestic house mouse, Mus musculus domesticus, were analyzed by flow cytometric analyses using mAbs to murine lymphocyte markers, and by polymerase chain reaction to study the TCR gamma and delta V gene repertoires. The majority of IEL in wild mice were CD3+, CD8+CD4- T cells. CD4+CD8- also were present in IEL isolates from wild mice, although at low numbers. Among IEL, but not T cells from the spleen or lymph nodes, there was a notable lack of Thy-1 expression, a preponderance of CD8 alpha alpha + T cells, and a relatively high ratio (3:1) of TCR gamma delta + T cells over TCR alpha beta + T cells, suggesting that some IEL in wild mice may develop via an extrathymic pathway similar to that described for laboratory mice. Analyses of the IEL gamma and delta variable genes revealed rearrangements of three of six V region gamma genes (V gamma 1, V gamma 2, and V gamma 5), with an abundance of V gamma 1 transcripts as determined by Northern blot analyses. For the delta gene, rearrangement of five of seven V region elements had occurred (V delta 2, V delta 3, V delta 4, V delta 5, and V delta 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Thymus influences the development of extrathymically derived intestinal intraepithelial lymphocytes.

Overwhelming evidence suggests that the majority of murine small intestinal intraepithelial lymphocytes (IEL) are extrathymically derived. These IEL include those with T cell receptor (TCR) gamma delta and some TCR alpha beta (CD8 alpha alpha and Thy-1-). In contrast, congenitally athymic nude mice have low numbers of gamma delta TCR IEL as well as very few alpha beta TCR IEL, far less than that would be expected if one assumes that gamma delta TCR IEL and alpha beta TCR (CD8 alpha alpha and Thy-1-) IEL in euthymic mice are extrathymically derived. To examine this discrepancy, we followed extrathymic IEL differentiation in IEL of day 3-thymectomized (NTX) mice as another athymic mouse model and found that gamma delta TCR IEL and extrathymically derived alpha beta TCR IEL in NTX mice are markedly reduced, almost to the level of nude mice. We further show that it is probably the absence of a thymic stroma that is responsible for the lower amounts of extrathymically derived IEL in nude mice, as the low amounts can be corrected to euthymic levels by syngeneic fetal thymus grafting but not by direct injection of F1 thymocytes. Lastly, unlike TCR/CD3+ extrathymically derived IEL, we noted a large proportion of extrathymic CD3-CD8- and CD3-CD8+ IEL; they were threefold more frequent in nude and NTX than in euthymic mice. This suggests that the thymus influences extrathymically derived IEL in its development from CD3- to CD3+ at the small intestinal epithelium.

Expression of the CD28 costimulatory molecule on subsets of murine intestinal intraepithelial lymphocytes correlates with lineage and responsiveness

The CD28 antigen has been recently demonstrated to be a costimulatory molecule and is expressed by almost all thymic and peripheral T cell receptor (TcR) alpha beta+ and gamma delta+ cells in the mouse system. We show here that expression of CD28 is heterogeneous among murine intestinal intraepithelial lymphocytes (IEL). Whereas some TcR alpha beta-expressing IEL subsets such as CD4+8- and CD4-8 alpha+ beta+ cells express CD28 at the same levels as their phenotypic counterparts in lymph node, other subsets of TcR alpha beta cells (including CD4-8 alpha+ beta- and CD4+8 alpha+ beta- cells) as well as TcR gamma delta+ IEL fail to express CD28. Parallel experiments using aged BALB/c-nu/nu mice indicated that CD28 expression patterns among IEL are quite similar to those of normal BALB/c mice. Furthermore, forward light scatter analysis showed that CD28- cells are considerably larger than CD28+ cells in the gut, although cycling cells were rare in both subsets. Finally CD28- cells in the gut did not proliferate or produce IL-2 upon stimulation by anti-CD3 monoclonal antibodies (mAb) and phorbol 12-myristate 13-acetate, whereas CD28+ cells in the gut and lymph nodes responded to these stimuli. The response of the CD28+ cells was enhanced by anti-CD28 mAb. These results suggest that CD28- IEL (CD4- 8 alpha+ beta- cells, and some CD4+ 8 alpha+ beta- cells) may follow a different developmental pathway from that of CD28+ IEL in a thymus-independent environment, and that expression of CD28 correlates with responsiveness of the cells to triggering via the TcR-CD3 complex.

CD2 expression on murine intestinal intraepithelial lymphocytes is bimodal and defines proliferative capacity.

The CD2 molecule is normally expressed on nearly all murine lymphocytes, and is co-stimulatory in T cell activation via the antigen receptor (TCR). A naturally occurring T lymphocyte population that is bimodal for CD2 expression was found in the intestinal intraepithelial lymphocytes (IEL). TCR alpha beta + IEL contain CD2- and CD2+ cells of approximately equal proportion, while TCR gamma delta + IEL are predominantly CD2-. The proliferative response of IEL to stimulation with an anti-CD3 mAb or with PMA plus ionomycin co-segregated with CD2 expression; the CD2+ subset proliferated vigorously under these conditions while the CD2- subset was much less responsive. The responding CD2+ IEL contained both TCR alpha beta + and TCR gamma delta + cells. However, activation of the CD2- IEL with anti-CD3 mAb resulted in only the expansion of TCR gamma delta + IEL, while activation with PMA plus ionomycin did not promote expansion of either the TCR alpha beta + or the TCR gamma delta + IEL. These findings parallel observations in the autoimmune lpr mouse, where massive numbers of peripheral TCR alpha beta + CD4-CD8- T cells that lack CD2 expression are also hyporesponsive to mitogenic stimulation. The apparent anergy of CD2- TCR alpha beta + IEL, as well as CD2- T cells from lpr mice, demonstrates that the absence of CD2 on TCR alpha beta + T lymphocytes co-segregates with nonresponsiveness.

Stimulation of murine intestinal intraepithelial lymphocytes by the bacterial superantigen staphylococcal enterotoxin B.

To gain insight into the specificity and function of intestinal intraepithelial lymphocytes (IEL), we have examined their response to staphylococcal enterotoxin B (SEB), a significant cause of food poisoning and a potent T cell mitogen. IEL include two populations of TCR alpha beta+ T cells. One of these resembles the T cells found in the Peyer's patch and is thymus dependent. The other subset is characterized by both TCR alpha beta and gamma delta+ IEL bearing a unique form of the CD8 molecule, expressed as an alpha alpha homodimer. CD8 alpha+ beta- IEL are thymus independent and appear to mature extrathymically in the gut epithelium. Two-color flow cytometric analysis showed that in vitro stimulation of IEL with SEB resulted in the expansion of the thymus dependent but not the thymus independent IEL; the CD8 alpha+ beta- IEL were functionally non-responsive to stimulation with SEB. 'Forbidden' self-superantigen reactive T cells present among IEL were also non-responsive to stimulation with SEB. The presence or absence of class II MHC molecules does not appear to play a role in the non-responsiveness to SEB, since CD8 alpha+ beta- IEL from class II deficient mice also failed to respond to stimulation with SEB. Depletion of CD8 beta+ and CD4+ T cells from total IEL decreased IL-2 production by IEL in response to cross-linking with anti-CD3, suggesting that the non-responsiveness of CD8 alpha+ beta- IEL extends to antigens other than SEB.