Cytokine production in patients with monoclonal gammapathies.

Increased interleukin-6 levels in culture media of mitogen-driven non adherent peripheral blood mononuclear cells were measurable in patients with monoclonal gammapathies of unknown significance but not in patients with multiple myeloma, indicating that in the former circulating mononuclear cells other than monocytes are involved in producing interleukin-6. Increased interleukin-4 levels were detected in supernatants of mitogen-driven peripheral blood mononuclear cells from patients with monoclonal gammapathies of unknown significance and from patients with multiple myeloma. The further increased interleukin-4 content in supernatants of non adherent cell cultures of multiple myeloma patients only suggests a somewhat inhibitory role of monocytes on interleukin-4 production, at least in multiple myeloma. Undetectable interleukin-2 levels in culture media were found in patients with monoclonal gammapathies of unknown significance and in patients with multiple myeloma. Serum levels of interleukin-6 and interleukin-2 were not measurable in either group, and interleukin-4 was detected only in a few patients. Our study suggests that in monoclonal gammapathies peripheral blood mononuclear cells could participate in producing cytokines involved in the regulation of B lymphocyte proliferation and differentiation. However, the pathophysiologic role in these patients of IL-6 and IL-4 in vitro, and possibly in vivo, produced by circulating lymphocytes remains to be established.