B cell stimulatory factor-1 (interleukin 4) prepares resting murine B cells to secrete IgG1 upon subsequent stimulation with bacterial lipopolysaccharide.

B cell stimulatory factor-1 (BSF-1)/interleukin 4 markedly enhances IgG1 and IgE secretion by B cells stimulated with bacterial lipopolysaccharide (LPS). We show that preincubation of resting B cells with BSF-1 alone prepares them to secrete IgG1, but not IgE, on subsequent stimulation with LPS. The ability of BSF-1 preincubation to increase overall viable cell yield on the subsequent addition of LPS only partially accounts for this enhancement. The degree of enhancement is dependent on the duration of preincubation, up to at least 48 hr. BSF-1 exerts this effect on resting B cells which have been selected for absence of surface IgG and in the presence of the reversible DNA synthesis inhibitor, hydroxyurea. BSF-1 can act to significantly enhance the IgG1 response when added for 48-hr periods before, at the same time as, or after the addition of LPS. These results suggest strongly that the mode of action of BSF-1 in preparing for the secretion of IgG1 is independent of that of LPS.