title: Phenotype, ontogeny, and repertoire of CD4-CD8- T cell receptor alpha beta + thymocytes. Variable influence of self-antigens on T cell receptor V beta usage.
abstract: We have characterized CD4-CD8- double negative (DN) thymocytes that express TCR-alpha beta and represent a minor thymocyte subpopulation expressing a markedly skewed TCR repertoire. We found that DN TCR-alpha beta + thymocytes resemble mature T cells in that they (a) are phenotypically CD2hiCD5hiQa2+HSA-, (b) appear late in ontogeny, and (c) are susceptible to cyclosporin A-induced maturation arrest. In addition, we found that DNA sequences 5' to the CD8 alpha gene were demethylated relative to their germline state, suggesting that DN TCR-alpha beta + thymocytes are derived from cells that had at one time expressed their CD8 alpha gene locus. Because DN TCR-alpha beta + thymocytes are known to express an unusual TCR repertoire with significant overexpression of V beta 8, we were interested in examining the possible role played by self-Ag in shaping their TCR repertoire. It has been suggested that DN TCR-alpha beta + thymocytes are derived from potentially self-reactive thymocytes that have escaped clonal deletion by down-regulating their surface expression of CD4 and/or CD8 determinants. However, apparently inconsistent with such an hypothesis, we found that the frequency of DN thymocytes expressing various anti-self TCR (V beta 6, V beta 8.1, V beta 11, V beta 17a) were not increased in strains expressing their putative self-Ag, but instead were either unaffected or significantly reduced in those strains. With regard to V beta 8 expression among DN TCR-alpha beta + thymocytes, V beta 8 overexpression in DN TCR-alpha beta + thymocytes appeared to be independent of, and superimposed on, the developmental appearance of the basic DN thymocyte repertoire. Even though V beta 8 overexpression appeared to be generated by a mechanism distinct from that generating the rest of the DN TCR-alpha beta + thymocyte repertoire, we found that super-Ag against which V beta 8 TCR react introduced into the neonatal differentiation environment also significantly reduced, rather than increased, the frequency of DN TCR-alpha beta + V beta 8+ thymocytes. Thus, the present study is consistent with DN TCR-alpha beta + thymocytes being mature cells derived from CD8+ precursors, and documents that their TCR repertoire can be influenced, at least negatively, by either self-Ag or Ag introduced into the neonatal differentiation environment. However, we found no evidence to support the hypothesis that DN TCR-alpha beta + thymocytes are enriched in cells expressing TCR reactive against self-Ag.
authors.affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Y
authors.initials: Y
authors.lastname: Takahama
authors.forename: A
authors.initials: A
authors.lastname: Kosugi
authors.forename: A
authors.initials: A
authors.lastname: Singer
mesh_terms: D000375:Aging / Q000276:immunology*; D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000235:genetics; D001483:Base Sequence; D016827:CD8 Antigens; D002454:Cell Differentiation / Q000187:drug effects / Q000276:immunology; D003524:Cyclosporins / Q000494:pharmacology; D016130:Immunophenotyping; D008745:Methylation; D051379:Mice; D008815:Mice, Inbred Strains; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000187:drug effects / Q000276:immunology*
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D016827:CD8 Antigens; D003524:Cyclosporins; D011948:Receptors, Antigen, T-Cell; D016693:Receptors, Antigen, T-Cell, alpha-beta