Relationship of age and sex to autoantibody expression in MRL-+/+ and MRL-lpr/lpr mice: demonstration of an association between the expression of antibodies to histones, denatured DNA and Sm in MRL-+/+ mice
Despite the protean nature of the clinical characteristics of systemic lupus erythematosus (SLE), autoantibodies represent an almost constant feature. Furthermore they are common to both human SLE and murine lupus. Nonetheless, the mechanism by which they arise has not been established. Amongst the several processes that have been proposed, evidence has emerged supporting specific antigen drive as a significant mechanism. We have documented the age- and sex-related differences in the prevalence of antibodies to both chromatin-related (histone and DNA) and non-chromatin-related (Sm) antigens in MRL mice. Our finding of an association between antihistone antibodies and anti-denatured DNA antibodies is consistent with chromatin being the putative antigen. Additionally, antibodies to the individual histones H1 and H2B, the most exposed histones in chromatin, were more prevalent than antibodies to the remaining histones (H2A, H3, H4). This, again, supports specific antigen drive as a mechanism for autoantibody production. However, associations were also found between antibodies to histone and DNA and antibodies to Sm. As Sm is a non-chromatin protein antigen, the associations between antibodies to Sm and those to histone and DNA suggest that mechanisms in addition to specific antigen drive are important in autoantibody production.