Rearrangement and junctional-site sequence analyses of T-cell receptor gamma genes in intestinal intraepithelial lymphocytes from murine athymic chimeras

Enterocyte expression of interleukin 7 induces development of gammadelta T cells and Peyer's patches

The intestinal mucosa is suggested to support extrathymic T cell development, particularly for T cell receptor (TCR)-gammadelta intraepithelial lymphocytes (IELs). TCR-gammadelta cell development requires interleukin (IL)-7; IL-7(-/)- or IL-7 receptor(-/)- mice lack TCR-gammadelta cells. Using the intestinal fatty acid binding protein (iFABP) promoter, we reinstated expression of IL-7 to mature enterocytes of IL-7(-/)- mice (iFABP-IL7). In iFABP-IL7 mice, TCR-gammadelta IELs were restored, as were cryptopatches and Peyer's patches. TCR-gammadelta cells remained absent from all other tissues. Likewise, T cell development in thymus and B cell maturation in the bone marrow and spleen retained the IL-7(-/)- phenotype. Thus, IL-7 expression by enterocytes was sufficient for extrathymic development of TCR-gammadelta cells in situ within the intestinal epithelium and was crucial for organization of mucosal lymphoid tissue.

Positive selection of gamma delta CTL by TL antigen expressed in the thymus

To elucidate the funciton of the mouse TL antigen in the thymus, we have derived two TL transgenic mouse strains by introducing Tl alpha 2-3 of A strain origin with its own promoter onto a C3H background with no expression of TL in the thymus. These transgenic mouse strains, both of which express high levels of Tla2-3-TL antigen in their thymus, were analyzed for their T cell function with emphasis on cytotoxic T lymphocyte (CTL) generation. A T cell response against TL was induced in Tg. Tla2-3-1, Tg. Tla2-3-2, and control C3H mice by skin grafts from H-2Kb/T3b transgenic mice, Tg.Con.3-1, expressing T3b-TL ubiquitously. Spleen cells from mice that had rejected the T3b-TL positive skin grafts were restimulated in vitro with Tg. Con.3-1 irradiated spleen cells. In mixed lymphocyte cultures (MLC), approximately 20% and 15% of Thy-1+ T cells derived from Tg.Tla2-3-1 and Tg.Tla2-3-2, respectively, expressed TCR gamma delta, whereas almost all those from C3H expressed TCR alpha beta. The MLC from Tg. Tla2-3-2 and C3H demonstrated high CTL activity against TL, while those from Tg. Tla2-3-1 had little or none. The generation of gamma delta CTL recognizing TL in Tg. Tla2-3-2, but not C3H mice, was confirmed by the establishment of CTL clones. A total of 14 gamma delta CTL clones were established from Tg. Tla2-3-2, whereas none were obtained from C3H. Of the 14 gamma delta CTL clones, 8 were CD8+ and 6 were CD4-CD8- double negative. The CTL activity of all these clones was TL specific and inhibited by anti-TL, but not by anti-H-2 antibodies, demonstrating that they recognize TL directly without antigen presentation by H-2. The CTL activity was blocked by antibodies to TCR gamma delta and CD3, and also by antibodies to CD 8 alpha and CD8 beta in CD8+ clones, showing that the activity was mediated by TCR gamma delta and coreceptors. The thymic origin of these gamma delta CTL clones was indicated by the expression of Thy-1 and Ly-1 (CD5), and also CD8 alpha beta heterodimers in CD8+ clones on their surfaces and by the usage of TCR V gamma 4 chains in 12 of the 14 clones. Taken together, these results suggest that Tla2-3-TL antigen expressed in the thymus engages in positive selection of a sizable population of gamma delta T cells.

Ontogenic development and tissue distribution of V gamma 1-expressing gamma/delta T lymphocytes in normal mice

A hamster monoclonal antibody (mAb) recognizing an epitope in the V gamma 1-J gamma 4-C gamma 4 chain of the gamma/delta T cell receptor has been generated. Using this mAb, we have quantitated the occurrence of V gamma 1-bearing gamma/delta T cells in the developing thymus and in the lymphoid organs and several epithelia of adult mice. The V gamma 1-expressing cells constitute a minor gamma/delta T cell subpopulation during fetal and early postnatal life, but they constitute a major population of gamma/delta T cells in the thymus and in the peripheral lymphoid organs in adult mice. In addition, we found that V gamma 1-bearing cells comprise a large proportion (15-60%) of the gamma/delta T cells present in the intestinal epithelium (i-IEL) in all strains of mice tested. V gamma 1+ i-IEL are present in athymic (nude) mice and in antigen-free mice, demonstrating that they can develop extrathymically and that their presence in the intestinal epithelium is independent of the antigenic load of the gut. Our results show that V gamma 1-bearing lymphocytes account for the largest population of gamma/delta T cells in the mouse. This population includes a thymus-dependent component that homes to the secondary lymphoid organs and a thymus-independent component that constitutes a major fraction of the gamma/delta i-IELs.

Oligoclonal repertoire of the CD8 alpha alpha and the CD8 alpha beta TCR-alpha/beta murine intestinal intraepithelial T lymphocytes: evidence for the random emergence of T cells

The epithelium of the small intestine in normal euthymic mice contains a large number of intraepithelial lymphocytes (IEL), some of which bear a T cell receptor alpha/beta (TCR-alpha/beta). About half of these TCR-alpha/beta IEL display the CD8 alpha alpha phenotype and the remaining have the CD8 alpha beta or the CD4 phenotypes. To examine whether TCR-alpha/beta IEL have a TCR-beta chain repertoire as diverse as that of TCR-alpha/beta lymph node lymphocytes (LNL), we used a recently described PCR technique that allows a global analysis of the TCR-beta chain repertoire. Within any given mouse, the repertoires expressed in both CD8 alpha alpha and CD8 alpha beta TCR-alpha/beta IEL populations are oligoclonal and nonoverlapping between the two subsets. The clones are largely conserved through the length of the small intestine of the same individual. However, genetically identical individuals raised under indistinguishable environmental conditions display distinct oligoclonal repertoires. Those findings indicate that few cells of CD8 alpha alpha or of the CD8 alpha beta phenotype are responsible for the repopulation of the intestinal epithelium.

The V delta 1 T cell receptor repertoire in human small intestine and colon

V delta 1 bearing T cells comprise the major population of gamma/delta T cells in the human intestinal tract. To gain insight into mechanisms involved in the generation of these cells and the diversity of their repertoire, we have characterized the junctional sequences of V delta 1 T cell receptor transcripts in the human small intestine and colon. Mucosal biopsies obtained from defined regions along the length of the small intestine or colon contained a high frequency of either one or a few identical in frame V delta 1 sequences. Less abundant sequences were also detected repeatedly throughout the length of small intestine or colon. Moreover, the intestinal V delta 1 repertoire in the small intestine and colon appeared compartmentalized and showed no overlap with the V delta 1 repertoire in peripheral blood. Dominant V delta 1 transcripts in each subject differed between the small intestine and colon, and the dominant transcripts within these sites differed among individuals. Analysis of small intestinal transcripts obtained at a 1-yr interval revealed that the V delta 1 repertoire was stable over time. The fact that the majority of V delta 1 transcripts, both dominant and rare, are distributed throughout a several meter length of the adult intestinal tract and are stable over time suggests they are not generated by an ongoing process of in situ VDJ gene rearrangement. Our results favor a model in which the repertoire of V delta 1 T cells in the intestinal tract is shaped by positive selection in response to a limited array of ligands before the migration of V delta 1 cells throughout the small intestine or colon.

Peripheral engraftment of fetal intestine into athymic mice sponsors T cell development: direct evidence for thymopoietic function of murine small intestine

Adult athymic, lethally irradiated, F1-->parent bone marrow-reconstituted (AT x BM) mice were engrafted bilaterally with day 16-18 fetal intestine or fetal thymus into the kidney capsule and were studied for evidence of peripheral T cell repopulation of 1-12 wk postengraftment. Throughout that time period, both types of grafts were macroscopically and histologically characteristic of differentiated thymus or intestine tissues, respectively. Beginning at week 2 postengraftment, clusters of lymphocytes were present within intestine grafts, particularly in subepithelial regions and in areas below villus crypts. As determined by immunofluorescence staining and flow cytometric analyses, lymphocytes from spleen and lymph nodes of sham-engrafted mice (AT x BM-SHAM) were essentially void of T cells, whereas in AT x BM thymus-engrafted (AT x BM-THG) mice, which served as a positive control for T cell repopulation, normal levels of T cells were present in spleen and lymph nodes by week 3 postengraftment, and at times thereafter. Most striking, however, was the finding that T cell repopulation of the spleen and lymph nodes occurred in AT x BM fetal intestine-engrafted (AT x BM-FIG) mice beginning 3 wk postengraftment. Based on H-2 expression, peripheral T cells in AT x BM-FIG mice were of donor bone marrow origin, and consisted of CD3+, T cell receptor (TCR)-alpha/beta+ T cells with both CD4+8- and CD4-8+ subsets. Peripheral T cells in AT x BM-FIG mice were functionally mature, as demonstrated by their capacity to proliferate after stimulation of CD3 epsilon. Moreover, alloreactive cytotoxic T lymphocytes were generated in primary in vitro cultures of spleen cells from AT x BM-FIG and AT x BM-THG mice, though not in spleen cell cultures from AT x BM-SHAM mice. Histologic studies of engrafted tissues 3-4 wk postengraftment demonstrated that thymus leukemia (Tl) antigens were expressed on epithelial surfaces of intestine grafts, and that both TCR-alpha/beta+ and TCR-gamma/delta+ lymphocytes were present in intestine grafts. Collectively, these findings indicate that the murine small intestine has the capacity to initiate and regulate T cell development from bone marrow precursors, thus providing a mechanism by which extrathymic development of intestine lymphocytes occur.