Activation events in hapten-specific B cells from tolerant mice

We have studied hapten-binding cells from the spleens of normal and tolerant adult mice in terms of their ability to enlarge, proliferate, and differentiate into antibody-secreting cells. Tolerant B cells showed clear defects in intermediate activation events in addition to a deficit in antibody-secreting cells. In these studies, isolated B cells were stimulated by T cell independent Ag with lymphokines, or with mitogens, in the absence of filler cells. The number of antibody-secreting cells generated from the tolerant population was consistently reduced by 70 to 80% of the control response to the specific Ag, fluoresceinated Brucella abortus (FL-BrA) ± lymphokines. We found that similar numbers of normal and tolerant cells enlarged (entered cell cycle) when stimulated by FL-BrA, LPS, IL-4, or α-Ig coupled to dextran (α-Ig-dex). Ia induction stimulated by IL-4, LPS, FL-BrA, or α-Ig-dex was the same in normal and tolerant cells. However, DNA synthesis stimulated by FL-BrA, FL-BrA + IL-5, or suboptimal concentrations of LPS was reduced by 70% in the tolerant cell population. Proliferation in response to 50 μg/ml LPS or to low doses of α-Ig-dex was similar in normal and tolerant B cells. These data suggest that the primary defect in adult B cell tolerance is the ability to proliferate in response to Ag.