The role of immune complexes in the pathogenesis of pleural effusions.

Thirty-two patients with pleural effusions (7 malignant, 5 with connective tissue disease, 5 with infections, 9 idiopathic, 6 miscellaneous) were studied to determine if immune complex formation might be involved in the pathogenesis of pleural fluid formation. Immune complexes were detected in serum, pleural fluid and in parietal pleural capillaries using direct immunofluorescence in the following groups: malignant disease (57%, 29%, 67%), connective tissue diseases (100%, 100%, 100%), infectious diseases (0%, 44%, 67%), idiopathic (67%, 44%, 75%), and miscellaneous (25%, 17%, 0%). Whereas the degree of immune complex was higher in serum than in pleural fluid in patients with malignant disease, the converse was true in patients with connective tissue diseases. Activation of C3 and properdin factor B was almost invariable in pleural fluid from patients with connective tissue disease and bacterial infections. These data suggested that pleural immune complexes are frequently associated with exudative pleural effusions. Immune complexes may lead to formation of pleural fluid by increasing capillary permeability. This may result from either a local Arthus-type reaction within the pleura, local immune complex formation within pleural fluid leading to release of inflammatory mediators, and/or deposition of circulating immune complexes in pleural vessels.