Tthyd, a new thymocyte alloantigen linked to Igh-1. Implications for a switch mechanism for T cell antigen receptors.

Tthyd is an alloantigen coded for by a gene(s) near the immunoglobulin locus on chromosome 12 in the mouse. This T cell-specific antigen may be the third member of a family of antigen receptors on T cells encoded by a cluster of genes in the IgT-C region. This antigen is preferentially expressed on thymocytes in contrast to Tindd or Tsud that are expressed on peripheral T cells. The hypothesis that T cell receptors undergo a switch in surface isotype upon maturation is discussed.