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Hypogammaglobulinemia in experimental myeloma: the role of suppressor factors from mononuclear phagocytes.

We have investigated the pathogenesis of the polyclonal hypogammaglobulinemia associated with BALB/c plasmacytomas TEPC-183 and SPQC-11 to gain insight into the hypogammaglobulinemia observed in human myeloma. With pokeweed mitogen-driven IgM biosynthesis by mouse splenocytes as the indicator system for suppression, we found that a protein extract of asscites cells obtained from these tumor-bearing animals could suppress immunoglobulin production, whereas like extracts from a non-suppressing plasmacytoma, modified RPC-5, caused no suppression in vitro. Extracts of tumor ascites depleted of mononuclear phagocytes by iron carbonyl treatment showed little suppressor activity. The active extract was not cytotoxic and contained no mycoplasma or common murine viruses. Furthermore, the active suppressor factor appears to be a low m.w. protein that is not affected by treatment with ribonuclease. These results and others are consistent with the idea that the hypogammaglobulinemia of myeloma is due to the formation of immunoregulatory macrophage-like cells which synthesize a suppressor substance.