Abstract
Circulating immune complexes (CIC) in eleven patients with mixed connective tissue disease (MCTD) were determined by C1q solid phase radioimmunoassay. A significant increase in the CIC level was observed in sera from patients with MCTD, as compared with those of progressive systemic sclerosis, polymyositis and normal controls. The CIC level in patients with MCTD, however, was much lower than that of systemic lupus erythematosus. It was associated with the disease activity in the most cases and a significant inverse correlation was observed between the CIC level and the serum C3 level. There was, however, no correlation between the CIC level and the titer of anti-RNP antibody.
By using the Western blot method, no RNP antigen was detected in the CIC obtained from all MCTD patients tested. On the other hand, substantial amounts of the anti-RNP antibody were detected in the CIC. The titer of the anti-RNP antibody in the CIC seemed to be associated with the CIC level, suggesting that the CIC may mainly be composed of the anti-RNP antibody.
