Effect of priming with antigen on the expression of C3 receptors on murine B cells and the responses to TI-2 antigens.

The effect of priming with DNP-Ficoll on the expression of receptors for the third component of complement (CR) on B cells was studied. B cells from mice primed with antigen were separated into CR- and CR+ populations by rosetting and density gradient centrifugation, and they were examined for antibody responses to TI-2 antigens in vitro. CR- B cells in spleen cells from mice primed with antigen responded well in contrast with the low responsiveness of CR- B cells from unprimed mice. These CR- B cells from primed mice reached their peak responses 1 day earlier than CR+ B cells from primed or unprimed mice. The response of these CR- B cells was specific for the hapten used for priming, and the priming effect was most conspicuous in spleen cells from mice primed with antigen 3 days previously, and it decreased thereafter. The CR- B cells from primed mice also showed better responses than CR+ B cells to all polyclonal B cell activators (PBA) tested. When CR+ B cells were primed in vitro with DNP-Ficoll for 3 days, the major cell population responsive to the antigen in secondary culture was found to be CR- B cells. On the other hand, CR- B cells in spleens could not respond to DNP-Ficoll challenge after in vitro priming with the antigen for 3 days. These results indicate that B cells lose CR by priming with antigen, although they retain their responsiveness to antigens and PBA. The role of CR on B cells in the antibody response is discussed.