Lipopolysaccharide (LPS) induced differentiation of mouse B lymphocytes to cells synthesizing large amounts of cytoplasmic IgM and IgG2 could be suppressed by antibodies to μ chains. Maximal inhibition of LPS induced differentiation was associated with increased cellular proliferation as measured by incorporation of 3H thymidine, whereas treatment with anti μ alone over a wide dosage range did not stimulate cellular proliferation. Spleen cells from newborn mice were suppressed by concentrations of anti μ several hundred fold lower than required for adult spleen cells; the adult pattern of susceptibility to suppression was acquired by 1 week of age. No significant differences in susceptibility to anti μ were found in comparisons of adult spleen, lymph node, bone marrow, and Peyer's patch lymphocytes.
