The regulation of growth and differentiation of a murine B cell lymphoma. I. Lipopolysaccharide-induced differentiation.

The B cell lymphoma WEHI 231 has been previously characterized as resembling a resting B cell, bearing large amounts of IgM on the cell surface, but not secreting immunoglobulin. When WEHI 231 cells were cultured together with low concentrations of lipopolysaccharide (LPS) (0.01 to 3 micrograms/ml), increased levels of immunoglobulin were detected in culture supernatants. Analysis by immunoprecipitation and gel electrophoresis demonstrated that this was secreted (19S) IgM. It was noted that small amounts of secretory IgM were produced even in control cultures not deliberately exposed to LPS. Analysis of the cell lysates showed that LPS treatment resulted in a reduction of synthesis of the surface form of IgM. In contrast, the cytoplasmic pool of IgM precursors was considerably expanded by LPS treatment, reflecting the overall increase in synthesis of IgM in LPS-treated cells. These changes in IgM metabolism appear to parallel closely those occurring in normal B cells after mitogen or antigen challenge. This cloned tumor line promises to be a valuable system in which to investigate some of the molecular events in B cell differentiation.