Relationship between natural and infection‐induced antibodies in systemic autoimmune diseases (SAD): SLE, SSc and RA

Our goal was to explore immunoserological relations between IgM and IgG isotypes of natural autoantibodies (nAAbs) and pathogen (or vaccine)‐induced or disease‐related antibodies in systemic autoimmune diseases (SAD); systemic sclerosis (SSc), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA). The found significant associations between IgG isotype nAbs and specific humoral antibodies may underscore the immune response‐inducible nature of the diseases investigated, and may corroborate the notion that nAbs can act as a mediator between the innate‐like and the adaptive arms of the immune system .The relationship between protective anti‐dsDNA IgM and the IgM isotype of anti‐F4 and anti‐CS may provide immuno‐serological evidence for the beneficial roles of nAAbs in SLE patients. Summary Infection or vaccine‐induced T cell‐dependent immune response and the subsequent high‐affinity neutralizing antibody production have been extensively studied, while the connection between natural autoantibodies (nAAbs) and disease‐specific antibodies has not been thoroughly investigated. Our goal was to find the relationship between immunoglobulin (Ig)M and IgG isotype nAAbs and infection or vaccine‐induced and disease‐related autoantibody levels in systemic autoimmune diseases (SAD). A previously described indirect enzyme‐linked immunosorbent assay (ELISA) test was used for detection of IgM/IgG nAAbs against citrate synthase (anti‐CS) and F4 fragment (anti‐F4) of DNA topoisomerase I in 374 SAD samples, with a special focus on systemic lupus erythematosus (SLE) (n = 92), rheumatoid arthritis (n = 73) and systemic sclerosis (n = 157) disease groups. Anti‐measles IgG and anti‐dsDNA IgG/IgM autoantibodies were measured using commercial and in‐house indirect ELISA tests. In all SAD groups the anti‐measles IgG‐seropositive cases showed significantly higher anti‐CS IgG titers (P = 0·011). In anti‐dsDNA IgG‐positive SLE patients, we detected significantly higher levels of anti‐CS and anti‐F4 IgG nAAbs (P = 0·001 and