Systemic lupus erythematosus and DNA antibodies in pleural effusions.

The quantity of antibodies to double-stranded DNA (ds-DNA) in 53 pleural effusions from 48 patients was measured by means of a modified Farr technique. In 10 samples, binding of ds-DNA was greater than 5 mg/l (range 6--14 mg/l), five samples being from patients with systemic lupus erythematosus (SLE), four from patients with lung cancer, and one from a patient with pulmonary tuberculosis. After treatment of pleural effusion samples with DNase, there was a marked increase of ds-DNA binding in the SLE group (n = 5), but none in the lung cancer group (n = 7) or in 4 patients with pleural effusions of various origin. In pleural fluid, demonstration of antibodies to ds-DNA and anti-ds-DNA-ds-DNA complexes, unmasked by DNase, may prove valuable when differentiating clinical conditions with pleural effusions.