IgG1 is the predominant subclass of in vivo- and in vitro- produced anti-tetanus toxoid antibodies and also serves as the membrane IgG molecule for delivering inhibitory signals to anti-tetanus toxoid antibody-producing B cells.

Peripheral blood leukocytes from individuals immunized with tetanus toxoid can be stimulated by pokeweed mitogen to produce IgG anti-tetanus toxoid antibody (IgG-Tet) in vitro. Previous studies have shown that treatment of these cells with tetanus toxoid or anti-human IgG reagents can inhibit this in vitro antibody synthesis. We have examined the four IgG subclasses on the surface of B cells for their relative contributions in the anti-IgG antibody-induced inhibition of IgG-Tet production. With all donors, the inclusion of anti-IgG1, but not anti-IgG2, -IgG3, or -IgG4, antiserum resulted in the in vitro inhibition of IgG-Tet synthesis. The magnitude of this inhibition was similar to that induced by treatment of the B cells with tetanus toxoid antigen. When the supernatants from normal in vitro cultures were assayed for IgG-Tet of the various IgG subclasses, it was observed that the IgG-Tet were almost exclusively IgG1. Similar results were obtained when serum IgG-Tet were measured. Thus, IgG1 appears to be the major subclass for (1) the in vivo-produced IgG-Tet, (2) the in vitro-produced IgG-Tet, and (3) the membrane receptor which can selectively convey an inhibitory signal to the IgG-Tet B cell.