In vitro immunoglobulin production by peripheral blood mononuclear cells from multiple myeloma patients and patients with benign monoclonal gammopathy. Regulation by cell subsets.

Peripheral blood mononuclear cells (PBM) from four patients with IgG myeloma and four patients with benign monoclonal gammopathy (BMG) were stimulated with pokeweed mitogen (PWM), and the in vitro immunoglobulin production over 7 days was measured with an enzyme-linked immunosorbent assay. All myeloma patients were sufficiently treated with cytostatic drugs. Their PBM did not produce monoclonal Ig in vitro, as opposed to PBM from two patients with BMG. Unseparated PBM from myeloma patients produced smaller amounts of polyclonal Ig than unseparated cells from normal donors. However, macrophage-depleted PBM from myeloma patients produced amounts of Ig comparable to those of normal donors when autologous or allogeneic adherent cells were returned in defined numbers. T cells from three of the four myeloma patients could provide help for the Ig production by B cells from healthy donors. These results indicate that functionally normal polyclonal B cells circulate in the blood of myeloma patients. The circulating T-cell population also has no obvious defect. In contrast, blood macrophages seemed to be altered with respect to their regulating function for polyclonal Ig production. The results obtained by using cell populations from patients with BMG did not differ from those of healthy people.