Effects of mu-specific antibodies on B cell growth and maturation

Over a wide range of concentrations affinity-purified rabbit anti-mouse mu chain antibodies, or their F(ab')2 fragments, inhibit the appearance of immunoglobulin-secreting cells (plaque-forming cells; PFC) in lipopolysaccharide-stimulated murine spleen cell cultures without affecting proliferation. Both IgM and IgG PFC are inhibited although the number of blasts bearing surface IgG remains unaltered. The IgM and IgG PFC response could be reconstituted to normal levels in cell cultures suppressed by mu-specific antibodies by the addition of supernatants from in vitro propagated helper T cell clones, or from EL4 lymphoma cells induced with phorbol ester. Interleukin 1-containing P388 supernatant, or recombinant DNA-derived murine interferon-gamma, did not reconstitute the PFC response in cell cultures suppressed by mu-specific antibodies, indicating that other factors are responsible for these effects. When spleen cell cultures, pre-activated with either lipopolysaccharide or monoclonal mouse mu-specific antibodies coupled to Sepharose, were exposed to EL4 supernatants in the presence of soluble mu-specific antibodies, maturation to secretion was inhibited while proliferation was not. The implications of these findings on assay systems for B cell growth and maturation factors are discussed.