Free serum ribonucleoprotein in mixed connective tissue disease and other connective tissue diseases

Free ribonucleoprotein (RNP) was found by means of a hemagglutination inhibition assay in 21 sera from 11 of 25 patients with mixed connective tissue disease (MCTD) who had 299 sera studied. Free RNP tended to appear when anti-RNP antibody titers fell or when prednisone was initiated or increased. Five of 72 SLE patients (211 sera) had free RNP in at least one serum. Three of them had anti-RNP antibodies in other sera. Free serum RNP was found in one of 20 patients with scleroderma and in two of seven patients with connective tissue disease "overlap" syndromes without anti-RNP.