A NATURAL IGM ANTIBODY DOES INHIBIT POLYCLONAL AND ANTIGEN-SPECIFIC IGM BUT NOT IGG B-CELL RESPONSES

Since a B-cell growth-inhibitory natural IgM antibody was identified i n the culture supernatants of LPS-stimulated murine splenic B lymphocy tes [11], attempts have been made to define other possible functional role(s) of this antibody. Here we show that this regulatory IgM is abl e to inhibit not only the proliferation of splenic B cells, but also t heir IgM secretion during LPS-induced polyclonal, as well as antigen ( FITC-KLH)-specific antibody responses. In contrast, Igc1 production of hapten (FITC)-specific B cells neither during restimulation with LPS nor in the presence of carrier-specific T lymphocytes in vitro was aff ected by regulatory IgM. Therefore, whereas newly emerging naive B cel ls are highly susceptible, IgG-secreting B cells appear to be complete ly resistant to inactivation by the regulatory IgM autoantibody.