Radioimmunoassays that use 125I-labeled protein A for determination of Histoplasma capsulatum-specific immunoglobulin G, A, and M class antibodies in histoplasmosis.

A radioimmunoassay for determination of human immunoglobulin G, A, and M class antibodies to Histoplasma capsulatum is reported. Yeast-phase antigen from H. capsulatum was adsorbed onto polyvinyl chloride microtiter plates as the solid phase. Human antibodies were allowed to react with this antigen, followed by addition of rabbit anti-human alpha- or mu-heavy chain sera. 125I-labeled staphylococcal protein A was then added and allowed to bind the human and rabbit immunoglobulin G. With this technique, it is possible to evaluate individual human serum samples for antigen-specific classes of antibodies. This assay may be useful for monitoring the immune response in histoplasma infections.