Regulation of an anti-self response: lack of influence of exogenous DNA on the in vitro anti-DNA response.

Abstract

Anti-DNA antibodies occur in outwardly normal individuals as well as in various forms of autoimmune disease. A number of publications have reported on the ability of added DNA to either induce or inhibit the in vitro production of anti-DNA antibody. In this study, the in vitro production of IgM anti-single stranded DNA (alpha ssDNA) antibody by spleen cells from normal or autoimmune mice neither depends upon, nor is inhibited by, the addition of high molecular weight DNA to the culture. The decrease in antibody forming cell plaques, reported previously, is due solely to the artifactual carryover of inhibitory material into the assay system, where it interferes with the expression of plaques by preventing anti-DNA antibody from reaching the DNA-coated erythrocytes. Similarly, plaque forming cell (PFC) methods have not detected alpha ssDNA antibody producing cells in murine spleen cells without culturing, but various other systems for measuring antibody normally detect anti-DNA antibodies in vivo. This discrepancy is also due to inadequate washing of freshly harvested cells to rid them of inhibitory substances which prevent them from registering as PFC. While S1 nuclease was able to prevent PFC interference by purified DNA, it did not remove the inhibitory substances from the culture supernatants; therefore substances other than ssDNA are able to interfere with alpha ssDNA PFC, suggesting that the alpha ssDNA PFC detected are polyspecific. Levels of alpha ssDNA PFC in spleen cells from non-autoimmune mice begin at one-quarter of the peak in vitro response, decrease to one-tenth in the first day and then reach peak values after 3 to 5 days of culture, suggesting that spleen cells are actively producing alpha ssDNA antibodies an in vivo and that then in vitro response is observed. Despite this evidence for an in vitro alpha ssDNA response, this response was not inhibited markedly by 1000 rad gamma-irradiation, while the response to sheep erythrocytes (SRBC) was profoundly suppressed. These findings suggest that anti-self B lymphocytes are resistant to interphase, possibly apoptotic, lymphocyte death due to gamma-irradiation, while anti-nonself B lymphocytes remain sensitive.