Objective       To investigate an early diagnostic marker for rheumatoid arthritis.       Methods      Two-dimensional electrophoresis and MALDI-TOF/TOF mass spectrometry were employed to screen and identify the specific autoantigen in the fresh synovial tissues from 2 patients with identified rheumatoid arthritis. ELISA was used to measure the antibodies in the 30 serum samples from patients with early rheumatoid arthritis and the 30 serum samples from healthy donors. The correlation between antibody levels and disease activity was analyzed.       Results        Manganese superoxide dismutase antibody was specific presence in the serum of early rheumatoid arthritis. The mean D(450) value of manganese superoxide dismutase antibody was 1.72±0.35 in early RA serum

significantly higher than normal serum (0.95±0.34

P0.0001). The levels of manganese superoxide dismutase antibody was positively correlated with levels of RF

CCP and CRP in patients with early RA. The positive rate for these serum samples was 63.3% to manganese superoxide dismutase antibody RA.       Conclusion        Manganese superoxide dismutase antibodies might be used as a biomarker for early diagnosis of rheumatoid arthritis and for prediction of disease activity.