Activation and proliferation signals in mouse B cells. V.A. comparison of the effects of intact (IgG) and F (ab')2 anti-mu or anti-delta antibodies.

This study compares the effects of soluble intact (IgG) and F(ab')2 rabbit anti-mu and anti-delta antibodies on mouse B cells. The results show that while the F(ab')2 antibodies to both isotypes induce polyclonal B cell proliferation, the IgG antibodies are not mitogenic, but rather inhibit DNA synthesis induced by the homologous F(ab')2 fragments. Furthermore, intact anti-mu antibodies inhibit mitogenesis induced by F(ab')2 anti-delta, and vice versa. However, the intact antibodies to both isotypes promote early changes characteristic of B-cell activation, namely, increased Ia antigen expression, and priming for a facilitated proliferative response to F(ab')2 anti-Ig. In addition, F(ab')2 anti-mu and anti-delta both induce the breakdown of phosphatidylinositol phospholipids in B cells, an early consequence of Ig receptor cross-linking which may be involved in the induction of cell growth. These results therefore indicate that stimulating mature B cells via IgM or IgD receptors produces indistinguishable early effects, and that cross-linking Fc and surface Ig receptors by intact anti-Ig generates a dominant inhibitory signal, regardless of which isotype is involved.