Nonspecificity of assaying for IgG antibody to pneumolysin in circulating immune complexes as a means to diagnose pneumococcal pneumonia.

Detection of immunoglobulin G (IgG) antibody to pneumolysin (PLY) in precipitated circulating immune complexes (CICs) has been used to diagnose pneumococcal pneumonia. With care to include appropriate controls, we precipitated and dissociated CICs and then assayed for IgG antibody to PLY. We detected IgG antibody to PLY in CICs that were precipitated from serum samples that were obtained at the time of admission to the hospital from 5 (23%) of 22 healthy adults, 7 (44%) of 16 subjects with stable chronic obstructive pulmonary disease, 10 (63%) of 16 subjects colonized with Streptococcus pneumoniae, and 9 (60%) of 15 patients with nonbacteremic pneumococcal pneumonia.