CD3-associated alpha/beta and gamma/delta heterodimeric receptors are expressed by distinct populations of CD4- CD8- thymocytes.

Immature double negative (DN) CD4-8- thymocytes expressing the CD3 molecular complex can be subdivided into two distinct subsets based on expression of the B2A2 antigen. Thus, B2A2+ CD3+ DN thymocytes express CD3-associated 35 kDa and 45 kDa polypeptide chains characteristic of a gamma/delta T cell receptor, whereas B2A2- DN thymocytes express predominantly 38 to 43 kDa CD3-associated structures typical of alpha/beta TCR. At the mRNA level, B2A2+ DN thymocytes express full length gamma and delta transcripts but no alpha message and only short (1 kb) B transcripts. In contrast, the B2A2- DN subset expresses full length alpha and beta transcripts and minimal levels of delta transcripts. Interestingly, B2A2- DN thymocytes, unlike mature T cells, also express abundant levels of full length TCR gamma mRNA, perhaps suggesting that these cells represent an early stage after divergence of the gamma/delta and alpha/beta T cell lineages.