Immunoglobulin M and G histoplasmal antibody response in histoplasmosis

Radioimmunoassays for IgM and IgG histoplasmal antibodies were developed and proved to be specific for their respective immunoglobulin classes, sensitive, and reproducible. Elevated IgM antibodies were detected in 59.8% of patients with histoplasmosis and 7.9% of control subjects. Elevated IgG antibodies occurred in 80.4% of patients with histoplasmosis but in only 12.9% of control subjects. Radioimmunoassay was nearly twice as sensitive as complement fixation for identifying patients with mild, presumably asymptomatic, infection. Of 13 patients with serologic follow-up at least 1 yr later, elevated IgM antibodies cleared, whereas IgG antibodies persisted in 7. In an epidemiologic investigation of a recurrent histoplasmosis outbreak, only the radioimmunoassay was able to prove the hypothesis that construction for a swimming complex was the source of exposure. These assays promise to be useful for clinical and epidemiologic investigations.