The effects of F(ab′)2 fragments of affinity-purified rabbit anti-human µ chain antibody (RaHµ) and rabbit anti-human δ chain antibody (RaHδ) on spontaneous and mitogen-stimulated immunoglobulin (Ig) secretion by normal human spleen cells were studied. IgM and IgG secretion by human spleen cells cultured in vitro was measured by incubating the cells with 3H-amino acids, precipitating the secreted labeled Ig with anti-Ig, and analyzing the precipitates by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Both RaHµ and RaHδ suppressed spontaneous and LPS-induced IgM and IgG secretion as well as PWM-stimulated IgG secretion. In different experiments, RaHµ and RaHδ either suppressed or augmented PWM-induced IgM secretion. The anti-Ig induced augmentation of PWM-triggered IgM secretion was most apparent when spleen cells were cultured at lower cell densities or when lower concentrations of anti-Ig were employed. These data indicate that perturbation of B cell surface immunoglobulin receptors with specific anti-Ig antibody can alter markedly the ability of these cells to differentiate into antibody-secreting cells.

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