Regulation of IgG antibody synthesis by a B cell component.

An immunoglobulin-G recruiting component (GRC) prepared from splenic B cells of antigen-primed mice was shown to be effective in recruiting more IgG plaque forming cells than normally appear among splenic cells experiencing a primary immune response. GRC caused increases in all classes of IgG PFC except perhaps IgG3, and the largest improvements were in IgG1 and IgG2a. GRC is synthesized by IgG2a-bearing cells and is effective at 96-120 h after spleen cells have been exposed to antigen. It is incapable of substituting for allogeneic effect factor, and the latter apparently must have its input on antibody producing cells before GRC can act. Together the data suggest that during a primary immune response a definite number of splenic B cells become poised for synthesizing IgG antibody, but only a portion of them are able to secrete. Apparently, the quiescent cells among them can be activated to secrete by exposure to GRC, A B cell product.