B-cell subsets responsive to fluorescein-conjugated antigens. III. Differential effect of E. Coli lipopolysaccharide on T-dependent and T-independent responses in vivo.

The effect of E. coli lipopolysaccharide (LPS) on the induction of both hapten-specific immunity and tolerance was studied in an in vivo system utilizing putative T-cell dependent (TD) or T-cell independent (TI) challenge antigens. The administration of LPS 1 day prior to challenge preempted the response of C3D2 mice to a TD antigen (FL-KLH) but had little effect on the response to FL-Ficoll, a TI antigen. LPS did not affect the responsiveness of C3H/HeJ mice, an LPS-unresponsive strain, to either antigen. The reduction of the response to a putative T-dependent antigen by LPS pre-treatment was only temporary since mice challenged 7 days after LPS responded normally in vivo. We also confirmed that LPS administered shortly after a tolerogen prevented FL-specific IgG tolerence induction and produced B-cell priming to a subsequent T-dependent antigenic challenge. LPS, however, did not significantly interfere with tolerance induction in terms of the IgM responce to either challenge antigen. These results suggest that LPS acts either directly or indirectly on a subpopulation of B cells responsive to a TD antigen. Our data further reflect the heterogeneity of B-cell subpopulations responsive to various polyclonal activators.