Clinical relevance of PM-1 antibody and physiochemical characterization of PM-1 antigen.

Using an improved immunodiffusion test with partially purified antigen, PM-1 antibody was identified in the serum of 18 patients. In 67% this system was associated with a polymyositis-scleroderma overlap, it occurred less frequently in polymyositis, dermatomyositis and scleroderma, and was not detected in other rheumatic diseases. The predominant clinical features of PM-1 positive patients were muscle weakness, sclerodactyly, Raynaud's phenomenon and pulmonary disease; widespread sclerodermatous features with infrequent. Characterization of the PM-1 antigen showed it to be a heat sensitive, trypsin sensitive acidic protein associated with the cell nucleus and possibly with nucleoli.