Novel 68 kDa autoantigen detected by rheumatoid arthritis specific antibodies.

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Abstract
OBJECTIVE--To improve the understanding of the pathogenesis of rheumatoid arthritis (RA) by identifying novel, disease specific autoantibodies. METHODS--Total protein preparations from synovial membranes were separated electrophoretically and immunoblotted. Sera from RA patients were screened for predominant immunoreactions by blotting. A 68 kDa antigen target of the most predominant reaction was detected and further characterised. RESULTS--The dominant immunoreaction in most of the RA sera tested was with a 68 kDa antigen. The antigen is probably ubiquitously expressed. It has an isoelectric point of 5.1, is O-glycosylated, and is located in the endoplasmic reticulum, the cytoplasm, or both. Antibodies to the 68 kDa autoantigen were present in 64% of 167 RA patients tested, and could also be detected in seronegative RA patients, but were present in only 1% of 98 patients with other rheumatic diseases. They could not be detected in 55 healthy controls. CONCLUSIONS--Because of its high sensitivity (64%) and specificity (99%), the anti-68 kDa autoantibody not only provides another valuable parameter for diagnosis, but also represents an antibody that may be involved in the pathological mechanisms leading to RA. This hypothesis can be tested by investigating if 68 kDa specific T cells are present in RA patients.