Regulation of B lymphocyte activation by the Fc portion of immunoglobulin.

Murine splenic B lymphocytes are induced to proliferate and undergo polyclonal activation in the presence of Fc fragments, AHGG, antigen-antibody complexes, and CH3 fragments derived from plasmin digestion of human Ig. The unifying feature of the polyclonal antibody response induced by these agents is that in all cases a portion of the constant region of the Ig molecule (ie, Fc region) is present. Fragments of Ig lacking the Fc piece, such as Fab and F(ab)2 were found not to be stimulatory. In addition, a model is proposed to account for the regulatory effects of antigen-antibody complexes on an ongoing humoral immune response.