The ontogeny of T lymphocytes

Functional T cell receptor delta chain gene messages in athymic nude mice

The rearrangement and expression of T cell antigen receptor (TcR) delta chain genes were investigated in congenitally athymic nude mice. The lymphoid cells derived from nude mice showed evidence of rearranged delta chain genes and a relatively high level of delta chain gene messages. Nucleotide sequence analysis revealed that nude mice contained an in-frame delta chain transcript, composed of V delta 5-D delta 1-D delta 2-J delta 1-C delta genes in the spleen. We have previously described functionally rearranged TcR gamma chain genes in the spleen of nude mice. Taken together, T cell precursors appear to proliferate and differentiate along the extrathymic pathway into TcR gamma/delta-bearing T cells in nude mice.

Rearrangement and expression of T cell antigen receptor and gamma genes during thymic development

Rearrangement and expression of the T cell antigen receptor and the gamma genes during T cell ontogeny is a regulated process; the gamma genes are rearranged and expressed first, followed by the beta and then the alpha genes. Expression of both functional alpha and beta gene RNA first occurs at day 17 of gestation, along with the expression of T3 delta chain RNA. T cell antigen receptor gene rearrangements occur primarily or exclusively in the thymus, although some gamma gene rearrangements occur outside the thymus in fetal liver cells that may be committed T cell progenitors. There is no gross difference in the extent of beta and gamma gene rearrangements in the adult thymocyte subpopulations that were analyzed, despite the fact that some of these populations cannot respond to antigen and never emigrate from the thymus. Quantitative analysis of rearrangements in total adult thymocyte DNA shows that beta gene rearrangements generally occur on both chromosomal homologs, and that rearrangements occur preferentially to the J beta 2 gene segment cluster.