Regulation of Fcγ R II expression and function by B lymphocyte activators

B lymphocytes cultured with LPS show increased expression of Fcγ R II and increased binding of Ag-IgG complexes (both > 200%). In contrast, B lymphocytes cultured with either IL-4 or anti-μ show a marked loss (85–90%) of binding of Ag-IgG complexes that is specific, time and temperature dependent, and reversible. Decreased binding of complexes was not due to decreased expression of the receptor and therefore appears to be due to some form of alteration of the receptor. Based on the observation that the loss of binding of complexes requires protein synthesis, we favor the view that the loss is due to association of Fcγ R II with another membrane molecule whose expression is induced or increased by IL-4 or anti-μ. Anti-μ induced loss of Fcγ R II ligand binding capacity does not require cross-linking of surface IgM because the effect can be generated with F(ab') anti-μ. Anti-μ induced loss of Fcγ R II binding of complexes was substantially prevented by IFN-γ, whereas IFN-γ did not reduce the anti-μ caused increase in expression of MHC class II molecules. This result shows that increased expression of the latter molecules can be dissociated from loss of Fcγ R II ligand binding capacity. A myeloid cell line was identified that constitutively expresses Fcγ R II binds relatively few complexes. This cell line may be useful in identifying alterations of Fcγ R II which lead to the loss of binding of complexes. These results indicate that various B lymphocyte activators have different effects on B lymphocyte expression and function, and can thereby affect Fcγ R II generated regulatory signals.