Immunoregulatory characteristics of the in vitro anti-ssDNA response

Continuous blockade of B-cell antigen receptors (BCRs) with Fab αsIg prevents the anti-ssDNA response of high, but not low, density B cells. Signaling via the BCRs, by prior exposure to crosslinking F(ab′)₂ αsIg, had no effect on the spontaneous anti-DNA response, but prevented a lipopolysaccharide-induced anti-DNA response. Pretreatment with intact αsIg, which provides exogenously derived Fc signals, reduced the response. An Fc-signal-blocking agent, F(ab′)₂ anti-IgG-Fc antibody, increased the number of anti-DNA antibody-forming cells produced in the absence of exogenous IgG anti-ssDNA antibody. Thus, activation is dependent on the availability of the BCRs, prior BCR crosslinking does not interfere with activation, and endogenous IgG anti-ssDNA antibody limits the activation of anti-ssDNA-specific B cells most of which are T-cell independent. These results indicate that the anti-ssDNA response is driven through the BCR.