Activation and proliferation signals in mouse B cells V. A COMPARISON OF THE EFFECTS OF INTACT (IgG) AND F(ab')2ANTI-γ OR ANTI-θ ANTIBODIES.

This study compares the effects of soluble intact (lgG) and F(ab')₂ rabbit anti-μ and anti-δ antibodies on mouse B cells. The results show that while the F(ab')₂ antibodies to both isotypes induce polyclonal B cell proliferation, the lgG antibodies are not mitogenic, but rather inhibit DNA synthesis induced by the homologous F(ab')₂ fragments. Furthermore, intact anti-μ antibodies inhibit mitogenesis induced by F(ab')₂ anti-δ, and vice versa. However, the intact antibodies to both isotypes promote early changes characteristic of B-cell activation, namely, increased la antigen expression, and priming for a facilitated proliferative response to F(ab')₂ anti-Ig. In addition, F(ab')₂ anti-μ and anti-δ 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 1gM or lgD receptors produces indistinguishable early effects, and that cross-linking Fc and surface lg receptors by intact anti-Ig generates a dominant inhibitory signal, regardless of which isotype is involved. [ABSTRACT FROM AUTHOR]