RESUMO
The alpha beta and gamma delta T cell receptors for antigen (TCR) delineate distinct T cell populations. TCR alpha beta-bearing thymocytes must be positively selected by binding of the TCR to major histocompatibility complex (MHC) molecules on thymic epithelium. To examine the requirement for positive selection of TCR gamma delta T cells, mice bearing a class I MHC-specific gamma delta transgene (Tg) were crossed to mice with disrupted beta 2 microglobulin (beta 2M) genes. The Tg+beta 2M- (class I MHC-) offspring had Tg+ thymocytes that did not proliferate to antigen or Tg-specific monoclonal antibody and few peripheral Tg+ cells. This is evidence for positive selection within the gamma delta T cell subset.
Assuntos
Receptores de Antígenos de Linfócitos T/metabolismo , Linfócitos T/imunologia , Animais , Divisão Celular , Epitélio/imunologia , Citometria de Fluxo , Antígenos H-2/imunologia , Antígenos de Histocompatibilidade Classe I/imunologia , Linfonodos/citologia , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Nus , Camundongos Transgênicos , Receptores de Antígenos de Linfócitos T/imunologia , Baço/citologia , Linfócitos T/citologia , Linfócitos T Auxiliares-Indutores/citologia , Linfócitos T Auxiliares-Indutores/imunologia , Linfócitos T Reguladores/citologia , Linfócitos T Reguladores/imunologia , Timo/imunologia , Microglobulina beta-2/genéticaRESUMO
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.