Antigen Receptor Repertoire Research Articles

Divergent evolution of T cell repertoires: extensive diversity and developmentally regulated expression of the sheep gamma delta T cell receptor.

Sheep gamma delta T cells express an unprecedented repertoire of antigen receptors contributed by increased diversity in both variable and constant region gene segments. Variable region diversity results mainly from the utilization of a large family of duplicated V delta genes that have retained two distinct hypervariable segments comparable with the complementarity determining regions present in other antigen receptor V genes. This implies that sheep V delta chains have been intensely selected during evolution, probably at sites involved in ligand recognition. The sheep gamma delta heterodimer occurs in at least five isotypic variants formed by the association of a single C delta segment with one of five functional C gamma segments, each with distinctive hinge regions. Our analysis also shows that the establishment of a normal peripheral repertoire is both developmentally regulated and dependent on the continual presence of a functional thymus during ontogeny. The existence of an expanded V gene repertoire and multiple receptor isotypes together with the prominence of gamma delta T cells in the sheep immune system argues that this lineage of T cells has a more elaborate functional role in this evolutionary pathway.

γδ T-cell development

γδ T cells consist of multiple lineages of cells with distinct antigen receptor repertoires, tissue localization and function. Recent evidence suggests that the ordered appearance of these sublineages during development is a result of programed rearrangement of Vy-gene segments. It appears that the T-cell receptor repertoire, at least of the γδ T cells with invariant receptors, is the result of site-directed rearrangement and cellular selection does not play a major role.

Is expression of the b-cell antigen receptor repertoire chaotic?

terization of uncommited B cell precursors from fetal liver at 12 days of gestation. EMBO J., 11, 593-601. Cumano, A., Paige, C.J., Iscove, N.N. & Brady, G. (1982), Bipotential precursors of B cells and macrophages identified in murine fetal liver at day 12 of gestation. Nature (Lond.), 356, 612-615. Kalled, S.L. & Broder, P.H. (1991), Utilization of VK families and VK exons. Implications for the available B cell repertoire. J. Immunol., 147, 3194-3200. Karasuyama, H., Kudo, A. & Melchers, F. (1990), The proteins encoded by the Vpre B and X 5 pre-B specific genes can associate with each other and with p heavy chain. J. exp. Med., 172, 969-972. Kincade, P.W. (1987), Experimental models for understanding B lymphocyte formation. Advanc. Immunol., 41, 181-267. Kudo, A. & Melchers, F. (1987), A second gene, VpreB in the 15 locus of the mouse, which appears to be selectively expressed in pre-B lymphocytes. EMBO J.,

Profound alteration in an alpha beta T-cell antigen receptor repertoire due to polymorphism in the first complementarity-determining region of the beta chain.

Amino acid residues that are critical in maintaining the framework structure of immunoglobulin heavy- and light-chain variable (V) regions are strongly conserved in the V alpha and V beta proteins of the alpha beta T-cell antigen receptor (TCR alpha beta). Consequently, it has been proposed that TCR alpha beta has a conformation similar to that of an immunoglobulin Fab fragment and that the regions of the TCR homologous to the three immunoglobulin complementarity-determining regions (CDRs 1, 2, and 3) bind to the peptide antigen-major histocompatibility complex (MHC) molecule ligand. A single amino acid substitution in the predicted CDR1 of the V beta 3 protein of certain mouse strains dramatically altered TCR alpha beta usage in an antigen-specific MHC-restricted immune response but did not abrogate V beta 3 specificity for the superantigens minor lymphocyte stimulatory locus (Mls)c and staphylococcal enterotoxin A (SEA). The results confirm the importance of the V beta CDR1 in antigen-MHC molecule recognition, supporting the Fab-like structural model of TCR alpha beta, and provide further evidence that conventional antigen-MHC recognition and superantigen recognition are mediated by distinct regions of the TCR beta chain. They also suggest that allelic polymorphism may be a significant source of diversity in the TCR repertoire.

Antigen receptors and adhesion molecules on T lymphocytes in the gut

The gut-associated lymphoid tissue represents an important site of initial contact with foreign antigens from the intestinal lumen. It is a complex immune system comprising of Peyer's patches, mesenteric lymph nodes, mucosal lymphocytes present in the lamina propria, and intraepithelial lymphocytes located on the luminal surface of the basement membrane and adjacent to the basolateral side of enterocytes. The function and immunoregulation of the gut-associated lyphoid tissue and its role in the pathogenesis of intestinal diseases are only partly understood. We summarize selected advances in understanding the cell-surface molecules involved in homing and adhesion of T cells in the gut-associated lymphoid tissue and the nature of the T-cell antigen receptor repertoire expressed by intraepithelial lymphocytes.

Lymphoid Dendritic Accessory Cells of the Rat

The expression of MHC class II antigens on potential APC is a crucial step in T-lymphocyte activation and the initiation of an immune response. The studies which are presented here were initiated to characterize the critical APC present in physiologically normal, untreated rats. Such a cell should constitutively express these antigens at high density and therefore provide the apparatus necessary to provoke both primary and secondary immune responses at any time. DAC were found to fulfill these criteria. In the absence of specific surface markers of rat DAC, the results are based on the strict combination of morphological appearance and functional activity. However, the high expression of MHC class II antigens may be regarded as semispecific markers for DAC which are distributed at strategic positions in many lymphoid and nonlymphoid tissues (Hart & Fabre 1981, Steiniger et al. 1984). The relatively low number of these cells observed in tissue sections and in in vitro isolates (0.1% of all cells) may explain their high activity as APC. This would facilitate the presentation of antigen in vivo to a sufficient number of competent T lymphocytes. DAC differentiate from a bone marrow progenitor cell pool preferentially under the influence of spleen cell-derived activities. Although the exact lineage has not yet been determined it may be fair to speculate that DAC form a new cell lineage probably related to interdigitating cells but not to macrophages which differentiate from bone marrow-derived precursors under the influence of colony-stimulating activities. However, the cooperation between DAC plus macrophages may provide the stage for T-lymphocyte activation and T-T collaboration (Mitchison 1990). There are still many open questions concerning the general role of DAC in vivo and in vitro. To further characterize rat DAC, their tissue distribution, role in the immune response and possible influence on intrathymic lymphopoiesis, with respect to T-lymphocyte subpopulations and the selection of the T-lymphocyte antigen-receptor repertoire, a panel of DAC-specific monoclonal antibodies must be generated in the future. Such antibodies will also be useful to study the mechanism by which DAC activate T lymphocytes.

B and T cell antigen receptor repertoires in lupus/arthritis murine models.

B and T cell antigen receptor repertoires in lupus/arthritis murine models.

T Cell Receptor Gene Trans-Rearrangements: Chimeric γ-δ Genes in Normal Lymphoid Tissues

Joining of V-, D-, and J-region gene segments during DNA rearrangements within all antigen receptor genes involves recognition of the same highly conserved heptamernonamer sequences flanking each segment. In order to investigate the possibility that recognition of these conserved sequences may sometimes permit intergenic joining of segments among different antigen receptor genes, DNA of normal human lymphoid tissues was examined by polymerase chain reaction amplification for the presence of chimeric gamma-delta T cell receptor gene rearrangements. These studies detected V gamma-(D delta)-J delta and V delta-(D delta)-J gamma rearrangements in thymus, peripheral blood, and tonsil. Analysis of thymus RNA indicated that many of these rearrangements are expressed as V gamma-(D delta)-J delta-C delta and V delta-(D delta)-J gamma-C gamma transcripts. Most transcripts (19 of 20 complementary DNA clones studied) are appropriately spliced and show correct open translational reading frames across the V-(D)-J junctions. Thus, chimeric antigen receptor genes are generated in a subset of normal lymphoid cells, probably as a result of chromosomal translocations, and such genes may possibly contribute to increased diversity within the antigen receptor repertoire.

Distinct antigen receptor repertoires of two classes of murine epithelium-associated T cells

T lymphocytes are found not only as recirculating cells in the lymphoid system, but also as immobile cells in certain epithelia. T-cell antigen receptors (TCR) of both alpha/beta and gamma/delta-heterodimer subtypes can exhibit an extremely high degree of diversity. The diversity of alpha/beta TCRs derives from the use of a large number of variable (V) gene segments, as well as junctional diversity generated during rearrangement of these segments, whereas the diversity of gamma/delta TCRs derives largely from junctional elements, with a smaller contribution from a limited number of V gene segments. Many T cells in the epidermal and intestinal epithelia of mice express TCR composed of gamma/delta heterodimers. We demonstrate here that gamma/delta TCRs of T cells in both these tissues are restricted in V gene usage, with different elements predominating. The TCR junctional diversity of epidermal T cells, however, is extremely limited, whereas that of intestinal T cells is extremely diverse. The distinctive features of these two populations suggest that they develop or are selected differently for particular tissue-specific functions.

Both rat and mouse T cell receptors specific for the encephalitogenic determinant of myelin basic protein use similar V alpha and V beta chain genes even though the major histocompatibility complex and encephalitogenic determinants being recognized are different.

Prospects for specific immune intervention in T cell-mediated autoimmune disease via anti-idiotypic regulation depend on the degree of diversity of the responder cell antigen receptor repertoire. A highly heterogenous response against self epitopes offers little chance for such regulation. We report here that the Lewis rat autoimmune disease experimental allergic encephalomyelitis, generally considered to be a model of human multiple sclerosis, is caused by T cells that use a limited set of TCR V genes. We have cloned the rat TCR alpha and beta chain cDNAs from the Lewis rat x mouse T cell hybridoma 510, which retains the rat specificity for the encephalitogenic determinant of myelin basic protein (MBP). Using Northern blot analysis of T cell RNA with the cloned V region probes, we have found a specific, and near perfect, correlation between expression of TCR message hybridizing to the V alpha 510 and VB510 probes and specificity for the encephalitogenic determinant of MBP in both T cell hybridomas and encephalitogenic T cell clones. This restricted V gene usage provides a basis for observed idiotypic regulation of auto-reactive T cells, and possible therapy for autoimmune disease. A curious and unexplained observation is that the Lewis rat V alpha/V beta combination that dominates the encephalitogenic response to the 68-88 peptide of MBP is precisely the same V alpha/V beta combination used by the B10.PL mouse response to the encephalitogenic response to the 1-9 peptide of MBP.

Positive selection of CD4+ thymocytes controlled by MHC class II gene products.

The mature T-cell antigen receptor repertoire is characterized by lack of reactivity to self-components as well as by preferential reactivity to foreign antigens in the context of polymorphic self-proteins encoded within the major histocompatibility complex. Whereas the former characteristic (referred to as negative selection or tolerance) is associated with intrathymic deletion of T cells expressing T-cell antigen receptor beta-chain variable (V beta) domains, which confer a preferential reactivity to self antigens, the existence of the latter (referred to as positive selection or MHC restriction) has so far only been inferred indirectly from functional studies. We show here that intrathymic deletion of V+beta 6 T cells (reactive with a self-antigen encoded by the Mlsa locus) is controlled by polymorphic MHC class II determinants. Furthermore, in mice lacking expression of Mlsa, the same class II MHC loci control the frequency of occurrence of V+beta 6 cells among mature CD4+ T lymphocytes. These data are direct evidence for positive selection by MHC determinants in the thymus in unmanipulated animals.

Development of T3/T cell receptor gene expression in human pre-T neoplasms

Acquisition of mature T cell function and the T cell antigen receptor repertoire occur in the thymus. In an effort to delineate the cascade of events leading to T cell maturation, we analyzed a series of clonal human precursor T cell neoplasms representing early, middle, and late stages of intrathymic differentiation. Rearrangements of the T cell receptor beta and gamma genes appear concurrently and are preceded by surface expression of the 3A1 (CD7) molecule. Subsequent transcription of the beta gene is coordinated with surface expression of T1 (CD5) and T11 (CD2), transcription of T3 delta mRNA, and the appearance of intracellular T3 (CD3) protein. As late events, T alpha gene transcripts appear and, finally, T3, the multichain complex linked to the T cell receptor, is presented on the cell surface. Findings reported here provide a model of the developmental orchestration of genes encoding antigen recognition in human T cells.

Development of T3/T Cell Receptor Gene Expression in Human Pre-T Neoplasms

Acquisition of mature T cell function and the T cell antigen receptor repertoire occur in the thymus. In an effort to delineate the cascade of events leading to T cell maturation, we analyzed a series of clonal human precursor T cell neoplasms representing early, middle, and late stages of intrathymic differentiation. Rearrangements of the T cell receptor beta and gamma genes appear concurrently and are preceded by surface expression of the 3A1 (CD7) molecule. Subsequent transcription of the beta gene is coordinated with surface expression of T1 (CD5) and T11 (CD2), transcription of T3 delta mRNA, and the appearance of intracellular T3 (CD3) protein. As late events, T alpha gene transcripts appear and, finally, T3, the multichain complex linked to the T cell receptor, is presented on the cell surface. Findings reported here provide a model of the developmental orchestration of genes encoding antigen recognition in human T cells.

Description of phenotypically distinct T-lymphocyte subsets which mediate helper/DTH and cytotoxic functions in the Syrian hamster.

Recent studies describe aberrations in the functions of T lymphocytes from Syrian hamsters. A current proposal links the apparent functional deficiencies of cytotoxic and suppressor T cells with anomalies found in class I molecules of this species (no polymorphism is detected) and speculates that hamsters possess limited heterogeneity of T cell subpopulations, particularly a class I-restricted subset. The present work tests this hypothesis by examining the extent of T cell heterogeneity defined by differential cell surface antigen expression. A panel of mouse monoclonal antibodies against hamster lymphocyte antigens was generated. MAb #20 and #110 bound to most, if not all, peripheral T cells; a third antibody, #38, divided T cells into two subpopulations which were functionally distinct. Cells within the #38-negative subset produced easily detectable IL 2 and mediated delayed-type hypersensitivity to influenza virus. In contrast, isolated 38+ cells produced little IL 2 and required the addition of exogenous T cell growth factor for proliferation to Con A. Treatment of immune cells with mAb #38 and complement abrogated cytolysis to TNP-haptenated or influenza-infected targets. Thus, Syrian hamsters possess at least two T cell subpopulations of discrete functional ability and unique cell surface antigen expression. Although the data suggest that T cells analogous to those of the class I-restricted, Lyt 2+ subset are present in the hamster, it is predicted that the scope of their composite antigen receptor repertoire may be limited by the monomorphism of class I molecules in this species.