Transmembrane signaling through B cell MHC class II molecules: anti-Ia antibodies induce protein kinase C translocation to the nuclear fraction.

Among receptors of immunologic importance, antigen receptors on B cells (mIg) and T cells (Ti/T3), as well as receptors for IL 2 and IL 3, appear to utilize a transmembrane signal transduction mechanism that involves protein kinase C (PKC) translocation from the cytosol to the plasma membrane. Here we report evidence that B cell surface type II major histocompatibility molecules (I-A and I-E) can act as signal transducing molecules, as evidenced by the ability of soluble ligands that bind these molecules to stimulate rapid translocation (less than 2 min) of cytosolic PKC. This phenomenon differs qualitatively from translocation induced by anti-Ig antibodies and all other ligands thus far studied, in involving an apparent translocation of protein kinase C to the nucleus. Data suggest that I-A/E molecules may play an active role in T cell-dependent B cell activation. They also provide an explanation for the previously observed suppressive effects of soluble I-A and I-E binding ligands on B cell activation in demonstrating that these ligands (anti-IA/E) deplete the cytosolic reservoir of PKC normally translocated to the plasma membrane after anti-Ig or LPS stimulation.