IFN-γ stimulates IgG2a secretion by murine B cells stimulated with bacterial lipopolysaccharide

rIFN-γ strikingly enhances the secretion of IgG2a by murine splenic B cells stimulated with bacterial LPS in vitro and concomitantly suppresses the production of IgG3, IgG1, IgG2b, and IgE while sparing IgM secretion. IFN-γ stimulates highly purified B cell populations to secrete IgG2a, strongly suggesting that it acts directly on B cells. It increases the frequency of precursors of IgG2a-expressing soft agar colonies and enhances the number of IgG2a⁺ cells in colonies indicating that it both increases the frequency of precursors of IgG2a⁺ cells and enhances the number of IgG2a⁺ daughter cells emerging from each precursor. IFN-γ completes its action within the first 24 to 48 h of a 6-day culture with LPS and its addition cannot be delayed beyond the first 48 h. Preincubation of resting B cells in the presence of IFN-γ leads to a time dependent increase, up to 42 h, in IgG2a secretion upon subsequent addition of LPS. IFN-γ can exert this action on resting B cells that have been selected for absence of membrane IgG expression by cell sorting. The promotion of IgG2a secretion appears to be a specific property of IFN-γ in that IFN-α, IFN-β, IL-1, IL-2, IL-3, IL-4, IL-5, granulocyte-macrophage-CSF, granulocyte-CSF, and CSF-1 fail to enhance IgG2a secretion by LPS-stimulated B cells.