Changes in the population and functional properties of antigen-specific rosette-forming B cells in antigen-primed mice by administration of polyclonal B-cell activator.

We have demonstrated that the number of rosette-forming cells (RFC) in the spleens of mice primed with sheep red blood cells (SRBC) was markedly decreased by administration of a polyclonal B-cell activator (PBA) such as the capsular polysaccharide of (CPS-K). Most of the RFC estimated were shown to be of B-cell type with Ig-receptors specific for SRBC. The precursor activity for the generation of anti-SRBC antibody-forming cells (AFC) (plaque-forming cells (PFC)) was closely associated with these RFC. Moreover, the precursor activity for the generation of AFC of RFC in the spleens of mice primed with SRBC and then treated with CPS-K (SRBC-primed and CPS-K-treated mice), as estimated by anti-SRBC PFC responsiveness to CPS-K, was much less than that of the same number of RFC in the spleens of SRBC-primed mice not treated with CPS-K especially at an early stage after injection of CPS-K. This low anti-SRBC PFC responsiveness of individual RFC in the spleens of SRBC-primed and CPS-K-treated mice resulted neither from an increase in some suppressing activity in the spleens of these mice nor from a relative increase in the number of RFC of non-B-cell type or non-SRBC-specific RFC. The percentage of the number of rosette-forming PFC in the total number of RFC seemed to be slightly increased in SRBC-primed and CPS-K-treated mice. However, this cannot totally explain the mechanism of the low responsiveness of RFC-fraction of spleen cells from SRBC-primed and CPS-K-treated mice. It has been concluded from these results that the signal mediated by PBA such as CPS-K acts on B cells bearing Ig-receptors specific for antigen (RFC) and changes a large number of them to the cells lacking Ig-receptors (non-RFC) and at least in part to the cells bearing Ig-receptors but showing low responsiveness to generate AFC following further stimulus (modified RFC).