MEMBRANE IMMUNOGLOBULIN IS CHARACTERIZED BY DISTINCT STRUCTURAL SUBPOPULATIONS

Membrane immunoglobulins are integral proteins on B cell surfaces that bind foreign antigens and are critically involved in the regulation o f the immune response. Based upon the model of serum IgG, it has been assumed that membrane immunoglobulins are essentially four chain disul fide-linked structures of the form H-2L2, where H represents an immuno globulin heavy chain, and L a light chain. We show here that membrane immunoglobulins of the mu and delta isotypes are present on spleen cel l surfaces in a much more diverse group of disulfide linked structures . In some cases mIg is linked into structures as large as H-5L5, while in other instances mu or delta chains appear to be linked by disulfid e interactions to non-immunoglobulin molecules. These various structur al complexes may represent distinct functional entities, as the associ ation of mIg with the cytoskeleton after mIg cross-linking appears to depend upon its structural subgroup.