Soluble deoxyribonucleoprotein (sNP) complexes in the pleural effusion of rheumatoid arthritis

In 2 to 3% of patients with rheumatoid arthritis (RA), associated pleurisy with effusion has been reported. In the RA patient described, complement activity evaluation in the pleural fluid showed nondetectable CH50 levels and markedly decreased C3 and C4 complement components. In addition, the fluid showed strong reactivity with isolated C1q, indicating the presence of aggregated γ-globulins and/or soluble immune complexes. The presence of anti-nuclear antibodies in the serum and their absence in the pleural effusion suggested than an excess of nuclear antigen might have absorbed the antibody activity with formation of soluble complexes. The nuclear antigen sNP (soluble nucleoprotein), a complex of native deoxyribonucleic acid and histones, in fact could be detected in the effusion. Furthermore, treatment of the fluid with deoxyribonuclease induced the appearance of anti-nuclear activity.