Possible roles of compound membrane receptors in the immune system.

A compound receptor is defined as a molecular complex which attains its final, biologically active structure by rearrangement and assembly in the membrane of several structural subunits. The existence of such receptor complexes is strongly suggested by experiments which demonstrated a very close association between certain ligand (primarily insulin) receptors and the major histocompatibility complex (MHC) antigens. We present here speculations on the possible role of MHC as a structural part of a multitude of receptors with different biological functions, and we argue that recent immunological data on minor histocompatibility antigens, antigen-presenting cells and T-lymphocyte receptors fit into this hypothesis.