We have shown that young autoimmune and normal strain mice possess autoantigen-sensitive cells potentially capable of producing anti-sDNA autoantibody in the absence of normal regulatory mechanisms in vitro. In certain strains such as B/W mice, these regulatory mechanisms presumably break down with increasing age, and autoimmunity develops. These regulatory mechanisms might consist of sDNA, T cells, or some combination of these since both of these agents suppressed the anti-sDNA PFC response in vitro. The sDNA may have inhibited PFC development by a receptor blockade mechanism since i) spleen cells pulsed with sDNA for short periods and then washed were suppressed after 5 days of culture; ii) treatment of these blocked cells with trypsin and DNase I restored the anti-sDNA response; iii) the PFC remaining in partially blocked cultures were of lower avidity than PFC in unblocked cultures; and iv) the target of sDNA may be a B cell.
Thymocytes and splenic T cells suppressed the anti-sDNA response but not the anti-SRBC response in vitro in a dose-dependent manner. The suppressive capacity of thymus cells did not decline with age in B/W mice. In addition, thymus cells activated by competing foreign antigens could also suppress the anti-sDNA response. The relationship between these modes of regulating autoreactivity remains to be investigated.