A novel family of human major histocompatibility complex-related genes not mapping to chromosome 6

Thymocyte antigens CD1 [Thy,gp45,12] are thought to be the human counterparts of mouse thymus leukaemia (TL) antigens 1,2 . Serological and biochemical analyses indicate that at least three subsets exist 3–6 , the first of which (HTA 1/T6) was initially identified by the monoclonal antibody NA1/34 (refs 7,8). Like TL, CD1 are expressed on cortical thymocytes as well as on some lymphoid neoplasias, and resemble in structure major histocompatabiliry complex (MHC) class I antigens. However HTA 1/T6 is loosely associated with β 2 -microglobulin 9–10 and is also found linked by a disulphide bridge to CD8 (T8) 11,12 . A molecular genetic approach is needed to investigate the CD1 system, to clarify its relationship to TL antigens and to understand its regulation. We report the isolation of complementary DNA (cDNA) clones encoding a CD1 antigen. These clones reveal a novel family of genes which are MHC-related but are neither equivalent to mouse TL antigens nor linked to the MHC.