The heavy chain of human B-cell alloantigen HLA-DS has a variable N-terminal region and a constant immunoglobulin-like region

Abstract

The HLA-D -region of the major histocompatibility complex (MHC) of man encodes polymorphic glycoproteins found predominantly on the cell surfaces of B cells and macrophages. These proteins mediate interactions, required for the induction of immune responses, among cells of the immune system and consequently are referred to as Ia (immune-response associated). Two families of Ia molecules, DR and DS (also known as DC), have been defined, the fomer analogous to the I–E (ref. 1) and the latter to the I–A molecules of the murine MHC^2–4. Both DR and DS molecules consist of two noncovalently associated polypeptide chains with molecular weights of 33,000 and 28,000, designated α and β, respectively. The polymorphism of DR molecules is due to structural variation in the small subunit, DRβ, with the large subunit, DRα, being constant in structure^5–7. In contrast, both subunits DSα and DSβ are structurally variable when DS allotypes are compared³. We have now isolated a cDNA clone from a DR7 cell line that contains the entire coding sequence for the DSα subunit and have compared its predicted amino acid sequence with that previously deduced from a DSα cDNA clone isolated from a DR4,w6 cell line⁸. This comparison reveals that 10 of 11 amino acid differences are located within the α1 (N-terminal) domain and that the α2 or immunoglobulin-like domains are identical.