A polyclonal model for B cell tolerance. I. Fc-dependent and Fc-independent induction of nonresponsiveness by pretreatment of normal splenic B cells with anti-Ig.

Abstract

We have developed a simple and adaptable, polyclonal model for B cell nonresponsiveness that is based on the inhibitory activity of anti-Ig as a surrogate for Ag. In our system the induction phase (treatment with anti-Ig) is separated from the challenge phase (Ag or mitogen), so that the critical events in each phase can be evaluated. Our results show that T cell-depleted B cells precultured for 18 to 24 h with rabbit anti-Ig reagents are rendered unresponsive to challenge with either Ag, fluorescein coupled to Brucella abortus (FL-BA), or mitogen (LPS). This state of nonresponsiveness (anergy) is reflected by an inhibition of a prototype response to the fluorescein hapten, as well as total Ig and IgG synthesis, but no reduction in proliferation to LPS. Interestingly, mitogen-induced polyclonal antibody formation was consistently reduced by 90% by treatment with either F(ab')2 or intact IgG anti-Ig. In contrast, the Ag-driven (FL-BA) response of pretreated B cells was inhibited by only 50 to 70%. Moreover, the latter effect usually required pretreatment with intact IgG anti-Ig, a result that suggests the importance of an Fc-dependent negative signal affecting the B cell's response to FL-BA. Furthermore, pretreatment and coculture of B cells with IL-4 blocked the Fc-dependent inhibition of the FL-BA responsiveness. These results, as well as kinetics experiments establishing a 4-h latent period, suggest that simple blocking of surface Ig receptor on target B cells is not responsible for the induction of anergy. Pretreated B cells displayed unique phenotypic changes after treatment with anti-Ig, including a diminution of Thy-1 expression in response to LPS + IL-4, as well as a reduction in membrane IgM and J11d expression (i.e., they were IgMlo, IgDmed, and J11dlo, as recently reported for anergic B cells in transgenic mice). These results suggest that B cell anergy can be induced in mature B cells by both Fc-dependent and Fc-independent processes that lead to unique phenotypic changes and may reflect egress from G0 in the absence of T cell help. The significance of these changes to tolerance mechanisms is discussed.