Nature of circulating immune complexes in infective endocarditis.

Two percent polyethylene glycol (PEG) precipitation was found to be a useful method for detecting circulating immune complexes (CIC) and could be used diagnostically to implicate infective endocarditis. Complexes consisting of a least Clq, IgG, and IgA were typically detected in sera from patients with infective endocarditis. Serial studies showed that CIC detection and measurement could be used to monitor clinical progress. Successful clinical improvement was reflected by decreasing CIC levels and the disappearance of rheumatoid factor, and, where increasing amounts of CIC were found, this may indicate situations where treatment was insufficient or inappropriate. There was specific free antibody demonstrable in the serum of six out of nine patients against their own infecting organisms, but attempts to identify the specificity of the complexed antibody as being directed against these organisms or their extracellular products failed. We could not detect any radioactive precipitin arcs, indicative of the free antibody also being in the complex, between the F(ab')2 preparation from the complex and the electrophoresed bacterial antigens in a radio-immunoelectrophoresis system. Eleven out of 13 sera that contained Clq, IgG, and IgA in their complexes also contained rheumatoid factor. Immunisation against the patient's own persisting CIC may explain this phenomenon.