Relationship between natural and infection -induced antibodies in systemic autoimmune diseases (SAD); SLE, SSc and RA.

BACKGROUND 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 relationship between IgM and IgG isotype nAAbs and infection or vaccine-induced and disease-related autoantibody levels in systemic autoimmune diseases (SAD). METHODS A previously described indirect 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 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. RESULTS 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 <0.001, respectively). Additionally, we found increased levels of IgM isotypes of anti-CS and anti-F4 nAAbs in anti-dsDNA IgM positive SLE patients (p=0.002 and 0.016, respectively). CONCLUSION The association between IgG isotypes of pathogen- or autoimmune disease-related antibodies and the IgG nAAbs may underscore the immune response-inducible nature of the diseases investigated. 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.