Effects of anti-IgM on mitogen-induced proliferation of human B-lymphocyte malignancies.

Therapeutic trials of anti-immunoglobulin antibody have produced a wide range of responses in attempts to control the growth of human B lymphoid neoplasms. This variability might reflect differences in intrinsic functional characteristics of malignant B lymphocytes that determine susceptibility to anti-immunoglobulin-mediated regulation of growth. To characterize B-lymphocyte malignancies, tissue samples from 24 patients were studied during short-term culture in vitro. Malignant B lymphocytes were stimulated to proliferate by the T-independent mitogens lipopolysaccharide, cytochalasin B, and Staphylococcus aureus that bears protein A. The effects of monoclonal mouse anti-human IgM on mitogen-induced malignant lymphocyte proliferation were then assessed. Mitogen-induced responses of malignant lymphocytes from three patients were abrogated by 2 micrograms/ml monoclonal anti-human IgM. Proliferation was also abrogated by polyclonal goat anti-IgM antiserum but proliferative responses were not affected by control monoclonal antibody. Further study showed that anti-immunoglobulin-mediated inhibition of proliferation was not dependent on Fc-determined interactions, nor was it dependent on the presence of T lymphocytes. These results indicate that a subset of human B-lymphocyte malignancies are susceptible to inhibition of proliferation mediated by anti-IgM.