Autoantibodies and antibodies to microorganisms in rheumatoid arthritis: comparison of histocompatible siblings.

A selection of antibodies to microorganisms were assayed on sera from a group of 12 pairs of HLA identical rheumatoid arthritis (RA) discordant siblings. Our results did not show any consistent quantitative or qualitative differences between RA and non-RA. However, autoantibodies were commoner and of higher titer in the subjects with RA. There was a difference in the antibodies to intrinsic antigens in RA which was not reflected in the antibodies to extrinsic antigens.