Effect of recent antigen exposure on the functional expression of B cell subpopulations

We investigated whether the definition of functional B cell subpopulations changes after the exposure of B cells to specific antigen. Recent in vivo priming with fluorescein- (FL) coupled T-independent (TI) antigens leads to an augmentation of the subsequent in vitro responses of B cells to FL-coupled TI antigens, including FL-polymerized flagellin, FL-lipopolysaccharide, and FL-Brucella abortus, as well as a FL-coupled T-dependent (TD) antigen, FL-keyhole limpet hemocyanin (KLH). This effect, which is evident 7 days after priming, is of short duration in that B cells from FL-Ficoll injected mice display normal responsiveness 3 wk after priming. When mice are primed with FL-KLH, the TD antigen, B cells responsive to a subsequent FL-KHL challenge are expanded, but no short-term cross-priming for any of the TI antigen challenges is observed. Limiting dilution precursor analysis shows that B cell populations responding to different FL-coupled TD and TI antigens overlap in unimmunized animals. FL-TI antigen priming induces not only quantitative changes in the responding B cells (increased precursor frequencies) but also results in functional changes in FL-specific B cells. The primed B cells now respond to FL-hapten in a carrier-restricted manner and behave as independent (non-overlapping) subpopulations. We suggest that B cell responses to different forms of the same hapten are influenced in part by their recent 'history' of antigen exposure.