SIMULTANEOUS ACTIVATION OF IG AND OCT-2 SYNTHESIS AND REDUCTION OF SURFACE MHC CLASS-II EXPRESSION BY IL-6

Terminal differentiation of B cells to plasma cells in vivo is charact erized by secretion of Ig and extinction of MHC class II expression on the cell surface. We show that IL-6 signaling leads to marked increas es in the synthesis and secretion of ig in clonal human B cell lines a nd newly isolated polyclonal B lymphocytes in vitro. The IL-6-induced cells resemble plasma cells in ultrastructure and in reduced expressio n of surface MHC class II. Enhanced Ig synthesis is a result of coordi nated transcriptional activation of Ig genes without promoter or isoty pe specificity, and differential accumulation of the mRNA encoding the secreted form of Ig heavy chain. It is saturable and subject to negat ive control when IL-6 stimulation is prolonged. Coordinate with tempor al changes in Ig synthesis, the DNA-binding activity and the synthesis of the B cell-enriched transcription factor Oct-2 are regulated. Thus , differentiation of B cells with IL-6 in vitro recapitulates the hall marks of terminal B differentiation in vivo; Oct-2 may have a role in this process.