The content of peripheral blood B cells (B1+) was reduced in patients of multiple myeloma (MM) and not in those with benign monoclonal gammopathy (BMG) compared to normal donors (P < 0.01). This observation correlated with the suppression of synthesis of normal immunoglobulin (Ig) in MM. Thus, cytokine activities regulating the proliferation of normal mature B cells, such as B cell stimulatory factor 1 (BSF‐1)/ inlerleukin 4 (IL‐4), B cell growth inhibitory factor (BIF) and IL‐2 in peripheral blood T cells, and IL‐1 in peripheral blood adherent cells, were investigated in patients with BMG (n ‐ 7) and MM (n = 28). All patients of MM having a marked suppression of synthesis of all other normal Ig, had significantly lower levels of BSF‐1 activity and inversely higher levels of BIF activity than those of normal donors. However, patients with BMG having no suppression of synthesis of normal Ig had BSF‐1 and BIF activities similar to normal donors. There was no significant difference in IL‐1 and fL‐2 activities between both normal donors and BMG versus MM patients. These data show that in MM altered cytokine activities correlate with suppression of synthesis of normal Ig.
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