B cell responses to a peptide epitope. VI. The kinetics of antigen recognition modulates B cell-mediated recruitment of T helper subsets

Abstract

The ability of Ag-primed B cells to recruit distinct Th subsets was examined using two analogous synthetic peptides, G41CT3 and G28CT3, as model Ags. With sequence differences at only two positions, these peptides were identical both with respect to fine specificity of Abs induced and ability to prime T cells. Lymph node cell populations primed with peptide G41CT3, when challenged with the homologous Ag, yielded predominantly Th2 cytokines. In contrast, a challenge with the heterologous Ag, G28CT3, resulted in a markedly increased production of Th1 cytokines. These distinctions derived from altered APC function of Ag-primed B cells due to differential kinetics of recognition of the two Ags by surface Ig receptors, as confirmed by binding studies with a panel of anti-G41CT3 mAbs. A concentration-dependent circular dichroism study revealed differences in the nature of intermolecular associations for these two peptides. Furthermore, the on-rate of peptide G28CT3 binding to Ab also increased with increasing peptide concentration, implying a dependence on intermolecular interactions. This, in turn, correlated well with the ability of peptide G28CT3 to preferentially activate either Th1 or Th2 cells. Thus, the relative proportion of Th1 vs Th2 cells recruited by Ag-primed B cells is governed by the on-rate of Ag binding to surface Ig receptors, with higher on-rates promoting Th1 recruitment. Further, even subtle changes in solution behavior of an Ag can markedly influence the kinetics of recognition by B cells.