Functional and Biochemical Characteristics of a Soluble B Lymphocyte Proliferation-Inhibiting Activity Produced by Bone Marrow Cells from Multiple Myeloma Patients

Several mechanisms are discussed as inducers for polyclonal hypogammaglobulinemia in multiple myeloma. A soluble noncytotoxic activity which inhibits in vitro the proliferation of normal polyclonal spleen B lymphocytes was measured in the supernatant of cultured bone marrow mononuclear cells from multiple myeloma patients. In addition, human B lymphoblastic cell lines (CESS, Daudi) and human T lymphocytes were sensitive to the antiproliferative effect of the suppressor activity, while other cell lines (RPMI 8226, IM9, CTL6, L12100 HL-60, and K562) were not. The activity was detected in a 5-kDa fraction and was stable to heating (30 min, 56°C) and proteolytic enzymes. Extraction experiments using chloroform:methanol (2:1) suggest a lipid character of the suppressor activity.