Characterization of a spontaneous murine B cell leukemia (BCL1). II. Tumor cell proliferation and IgM secretion after stimulation by LPS.

A spontaneous BALB/c B lymphocyte leukemia could be stimulated in vitro by the polyclonal B cell activator lipopolysaccharide (LPS) and the conditions for activation were studied. Spleen cells or peripheral blood lymphocytes from tumor-bearing animals responded by increased DNA synthesis and the peak of activation occurred earlier than with normal mouse spleen cells. Tumor cells harvested from the spleen, but not from the peripheral blood, could be induced by LPS to secrete IgM. Direct demonstration that the response was due to tumor cell activation and not that of contaminating normal B lymphocytes was provided by karyotype analysis and by immunoprecipitation, which showed the restriction of light chains on secreted IgM molecules to the lambda isotype.