T lymphocytes differentiate and mature in the thymus. It is here that thymocytes with reactivities to self antigens are eliminated and those with specificities to 'altered' self-major histocompatibility complex (MHC) gene products are positively selected1. The selections are presumably carried out on the basis of their T-cell antigen receptors (TcR). The genes of the α- and β-chain T-cell antigen receptors have been cloned 2-7. A third T-cell specific gene capable of undergoing somatic rearrangement has also been identified8; the role of this third gene is not known. An order of expression of γ, β, then α is found during T-cell ontogeny9,10. But although α- and β-chain messages are often functional11-15, γ transcripts are rarely functional in thymocytes or mature T cells16-18. To define the sequential order of expression of these genes further and to continue the search for a possible role for the TcR γ gene products, we investigated the expression of 'functional' α-, β- and γ-chain transcripts in young athymic mice. These mice express an undetectable amount (less than one in 8 × l05 spleen messages) of 'full-length' α- and β-chain T-cell receptor transcripts, but an increased level of expression of 'full-length' γ chain messages. Nucleotide sequence analysis of four γ complementary DNAs show that all four γ transcripts sequenced are functional. These findings suggest that γ gene products may be important in a prethymic or extrathymic pathway and may represent a second type of T-cell recognition, possibly in a lineage in which α and β genes are not used.
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