Terrence A. Barrett

T cell activation causes diarrhea by increasing intestinal permeability and inhibiting epithelial Na+/K+-ATPase

Inflammatory bowel disease (IBD) is associated with mucosal T cell activation and diarrhea. We found that T cell activation with anti-CD3 mAb induces profound diarrhea in mice. Diarrhea was quantified by intestinal weight-to-length (wt/l) ratios, mucosal Na(+)/K(+)-ATPase activity was determined and ion transport changes were measured in Ussing chambers. Anti-CD3 mAb increased jejunal wt/l ratios by more than 50% at 3 hours, returning to base line after 6 hours. Fluid accumulation was significantly reduced in TNF receptor-1 (TNFR-1(-/-)), but not IFN-gamma knockout mice. Anti-CD3 mAb decreased mucosal Na(+)/K(+)-ATPase activity, which was blocked by anti-TNF mAb and occurred to a lesser degree in TNFR-1(-/-) mice. Neither alpha nor beta subunits of Na(+)/K(+)-ATPase decreased in abundance at 3 hours. Intestinal tissue from anti-CD3-treated mice exhibited increased permeability to mannitol at 1 hour and decreases in electroneutral Na(+) absorption, Na(+)-dependent glucose absorption, and cAMP-stimulated anion secretion at 3 hours. Furthermore, enteral fluid accumulation was observed in CFTR(-/-) mice, indicating a minor role of active anion secretion. These data suggest that diarrhea in IBD is due to TNF-mediated malabsorption rather than to secretory processes. T cell activation induces luminal fluid accumulation by increasing mucosal permeability and reducing epithelial Na(+)/K(+)-ATPase activity leading to decreased intestinal Na(+) and water absorption.

Repertoire Development and Ligand Specificity of Murine TCRγδ Cells

During the past several years, we have been studying the circulating TCR gamma delta cells expressed in peripheral lymphoid tissues. Biochemical and molecular characterization of the TCR gamma delta heterodimers present on these TCR gamma delta cells identified 3 TCR gamma proteins, V gamma 2-C gamma 1, V gamma 1.2-C gamma 2, and V gamma 1.1-C gamma 4. In addition, at least 6 different V delta gene products (V delta 2,4,5,6,V alpha 10, V alpha 11) are expressed in peripheral lymphoid tissue. Nucleotide sequence analysis has revealed a great deal of junctional diversity present among the different V gamma and V delta proteins. Thus, compared to other nonlymphoid tissues (e.g., skin), this population of TCR gamma delta cells appears quite extensive. The development and specificity of TCR gamma delta cells has been pursued by two approaches. First, different TCR gamma delta cells clones were generated which recognize MHC-encoded gene products. One clone recognizes an unconventional TL-encoded antigen, whereas others have been shown to recognize either classical MHC class I or class II antigens. The TCR gamma delta receptor genes have been cloned from the TL-specific TCR gamma delta cell and used to construct transgenic mice to examine the development of TCR gamma delta cells. Although the Tg+ TCR gamma delta cells are tolerized by thymic clonal tolerance similar to TCR alpha beta cells, the epithelial Tg+ TCR gamma delta cells are subjected to non-deletional tolerance (anergy). A second approach towards examining the development of TCR gamma delta cells has been to compare the repertoire of TCR gamma delta splenocytes in a variety of inbred and MHC-congenic strains of mice using subset-specific anti-murine TCR gamma delta mAb. The percentage of individual subsets of splenic TCR gamma delta cells differ widely between different inbred strains of mice due to both MHC- and TCR-encoded genetic differences. In summary, these studies provides a basis for understanding and determining the ligand(s) of the TCR gamma delta heterodimer and the factors which shape the peripheral TCR gamma delta repertoire.

Development of TCR γ δ Cells

Over the past several years, a novel T cell subset has been identified that, unlike conventional CD8+ cytolytic cells and CD4+ helper TCRαβ cells, expresses a T cell receptor complex (TCR) composed of CD3-associated, disulfide-linked TCR γ and δ gene products (Bluesfone et al. 1991a). The role of TCRγδ cells in immune responses is currently not well understood. TCRγδ T lymphocytes appear in enhanced numbers in skin lesions of Mycobacterium leprae, celiac sprue, polymyositis, listeria infections, and in the synovial fluid of joints affected by rheumatoid arthritis (Reviewed in Immunol. Rev. Vol. 120, 1991). These observations raise the possibility that this subset of T lymphocytes may play a role in the control of infectious processes and in autoimmune disease. The TCRγδ cells develop in waves in the thymus prior to TCRαβ development with each successive wave expressing a distinct family of TCR Vγ and Vδ genes (Raulet, 1989). In fact, unlike TCRαβ cells, TCRγδ cells selectively home to specific tissues including the skin, lung, reproductive tract and intestine where they reside as intraepithelial lymphocytes (IEL) (Bluestone et al. 1991b). In addition, TCRγδ cells occupy anatomically distinct regions of the lymphoid tissue, such that splenic TCRγδ cells predominate in the sinusoids while the TCRas cells localize to the follicular areas. In spite of the great potential for diversity in this population, the TCRγδ cells have a more limited TCR repertoire than as cells especially in the regional epithelial tissues where in some cases a single TCRγ and δ chain is expressed on resident cells.

Development of TCRγδ Cells

Over the past several years, a novel T cell subset has been identified that, unlike conventional CD8+ cytolytic cells and CD4+ helper TCRαβ cells, expresses a T cell receptor complex (TCR) composed of CD3-associated, disulfide-linked TCR γ and δ gene products (Bluesfone et al. 1991a). The role of TCRγδ cells in immune responses is currently not well understood. TCRγδ T lymphocytes appear in enhanced numbers in skin lesions of Mycobacterium leprae, celiac sprue, polymyositis, listeria infections, and in the synovial fluid of joints affected by rheumatoid arthritis (Reviewed in Immunol. Rev. Vol. 120, 1991). These observations raise the possibility that this subset of T lymphocytes may play a role in the control of infectious processes and in autoimmune disease. The TCRγδ cells develop in waves in the thymus prior to TCRαβ development with each successive wave expressing a distinct family of TCR Vγ and Vδ genes (Raulet, 1989). In fact, unlike TCRαβ cells, TCRγδ cells selectively home to specific tissues including the skin, lung, reproductive tract and intestine where they reside as intraepithelial lymphocytes (IEL) (Bluestone et al. 1991b). In addition, TCRγδ cells occupy anatomically distinct regions of the lymphoid tissue, such that splenic TCRγδ cells predominate in the sinusoids while the TCRas cells localize to the follicular areas. In spite of the great potential for diversity in this population, the TCRγδ cells have a more limited TCR repertoire than as cells especially in the regional epithelial tissues where in some cases a single TCRγ and δ chain is expressed on resident cells.

Control of self-reactivity in the intestine

SummaryIn the intestine maintenance of self-tolerance may involve tissue-specific self-Ags, APCs, ‘second signals’, and extrathymic pathways of T cell maturation. These factors combine to create a unique environment where autoimmune tissue destruction is prevented despite local inflammatory influences. In this review we summarize our findings using a TCR-γδ transgenic model where self-tolerance was maintained by clonal deletion for cells localizing to peripheral lymphold tissue and by clonal anergy for cells localizing to the intraepithelial compartments. Several possible explanations exist for these results but in general, these findings have implications for the maintenance of self-tolerance of normal TCR-αβ and TCR-γδ IELs in epithelial tissues such as the intestine.