Discordant distribution of IgM and IgG antibodies to DNA and RNA in monozygotic twins with systemic lupus erythematosus.

Sera from six sets of twins (five monozygotic and one dyzygotic) in whom one or both has systemic lupus erythematosus (SLE) were evaluated for antibodies to DNA and RNA. Sera from three monozygotic twin sets were further studied to determine the distribution of 19S and 7S antibodies to DNA and RNA. The presence of significant binding of polyriboadenylic acid and of native DNA correlated with the presence of clinical SLE in this study. Sucrose density gradient fractionation studies of the sera revealed that the clinically normal twins had some binding of Poly A and DNA limited to the 19S region, whereas the twins with SLE generally had significant levels of 19S and 7S antibodies to DNA and/or Poly A. On the other hand, concordance for presence or absence of antibodies to doublestranded RNA was demonstrated within each twin set irrespective of concordance or discordance for clinical SLE. These results suggest that genetic factors may be important in determining which nucleic acids antigens become immunogenic, but genetic factors alone do not determine the immunoglobulin class distribution of antibodies to nucleic acids.