Thermodissociation of staphylococcal immune complexes and detection of staphylococcal antigen in serum from patients with Staphylococcus aureus bacteremia.

We describe a simple and rapid method to dissociate antigen-antibody complexes to allow antigen detection by radioimmunoassay. Immunoglobulins and immune complexes were precipitated from serum in 50%-saturated ammonium sulfate. The precipitate was dissolved in distilled water and heated at 90 degrees C for 15 min to free the antigen and denature the antibody irreversibly. With this treatment, the sensitivity for detecting staphylococcal antigen added to human serum improved greater than or equal to 16-fold and was similar to the sensitivity in buffer. After intravenous injection of antigen into a rabbit with high levels of staphylococcal antibodies, antigen was detected only after thermodissociation. Also, in 4 of 26 patients with Staphylococcus aureus bacteremia, circulating antigen was detected after thermodissociation. Thermodissociation of immune complexes is a simple, rapid method and should be useful for detecting other heat-stable antigens.