IgM antiplatelet antibodies in 7 out of 20 rheumatoid arthritis sera. A new antiplatelet antibody ELISA. Reverse correlation with anti-B-lymphocyte antibodies in the same sera.

In a previous work, we had found that anti-B lymphocyte antibodies exist in rheumatoid arthritis. To investigate whether these antibodies were directed against surface immunoglobulins or not we have investigated if RA sera could recognize similar structures on other targets such as platelets (on which immunoglobulins and immune complexes are present) by a new ELISA method. No IgG antiplatelet antibody was found in 20 RA sera. But 7 out of these 20 RA sera had IgM antiplatelet antibodies when tested on platelets from 5 donors. The comparison of the positivities of these sera on B lymphocytes and platelets from the same donors showed a statistically significant reverse (X2 = 20,008, p much less than 0.0001) correlation. The target antigen and the meaning of these IgM antiplatelet antibodies, which seem to be associated with severe RA, is still under investigation.