Complement activation in systemic sclerosis.

The use of a synthetic protease inhibitor, nafamstat mesilate, has enabled reliable estimations of in vivo complement activation to be made in patients with systemic sclerosis. Elevations of C3a and C4a anaphylatoxins were found in 2 and 24 out of 30 patients respectively, indicating that complement activation, predominantly by the classical pathway, is a common occurrence in the disease, even though complement C3 and C4 levels were within the reference range.