Cell surface immunoglobulin: XVIII. Functional differences of B lymphocytes bearing different surface immunoglobulin isotypes*

Three populations of murine splenic B lymphocytes have been characterized previously (6, 7, 9) as those bearing only IgM, those bearing only IgD, and a population bearing both isotypes. These studies were designed to test the response of the IgM⁺ cells (IgM-only or IgM plus IgD) vs. the IgD-only cells to the B-cell mitogen, lipopolysaccharide. Results suggest that after 1-4 days of culture, in the presence of mitogen, the IgM⁺ cells enlarge and elaborate an IgM polyclonal response. The IgD-only cells, in contrast, do not exhibit an IgM polyclonal response, but instead undergo blastogenesis and proliferation.