Triggering of lymphocytes by antibodies against beta2 microglobulin

beta2 microglobulin (beta2m), structurally related to "domains" of immunoglobulin molecules, is associated with products of the major histocompatibility system on cell surfaces. Heteroantibodies against beta2m are mitogenic to a specific subpopulation of human and mouse B lymphocytes. This subpopulation is present in human blood which makes the antibody convenient and clinically useful as a functional marker for peripheral B lymphocytes. Absorption and elution experiments, as well as tests showing mitogenic activity of Fab monomers of anti-beta2m indicate that the interaction of the binding site of the antibody and relevant cell surface structures, probably beta2m itself, is directly responsible for lymphocyte activation. The relevance of these findings for cell receptors involved in lymphocyte activation is discussed.