Demonstration of circulating pneumococcal immunoglobulin G immune complexes in patients with community-acquired pneumonia by means of an enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay was developed for quantitation of circulating immune complexes (CICs) containing specific antipneumococcal immunoglobulin G (IgG). These CICs were detected in 17 (85%) of 20 patients with bacteremic pneumococcal pneumonia, 4 (36.4%) of 11 patients with probable pneumococcal pneumonia, 3 (16.7%) of 18 patients with pneumonia of other (nonpneumococcal) etiology, and 13 (41.9%) of 31 patients with pneumonia of unknown etiology. There was no correlation between CICs and serum IgG antibody levels. Pneumococcal capsular antigen was demonstrated in dissociated CICs by latex agglutination.