Monocyte-T-cell interactions in the regulation of polyclonal B-cell response

Human peripheral blood monocyte subsets with and without Fc receptor for human IgG are known to suppress (FcR+) and enhance (FcR-) pokeweed mitogen-induced polyclonal immunoglobulin synthesis in vitro. The ability of these subsets to modulate immunoglobulin production in the presence or absence of OKT8+ T cells and under conditions where suppressor T-cell activation was blocked by irradiation or mitomycin C was studied. It was shown that, regardless of the presence or absence of suppressor T cells, FcR+ monocytes can suppress immunoglobulin production if their number in culture exceeds 20%. However, at lower numbers this monocyte subset was suppressive only when suppressor T cells were activated. The suppressor T-cell activation was shown to be independent of the predominant presence of the FcR+ or FcR- monocyte subset. Moreover, the enhancing effect of FcR- monocytes was not caused by their interference with suppressor T-cell activation.