Comparison and diagnostic value of the coccidioidin heat-stable (HS and tube precipitin) antigens in immunodiffusion

Coccidioides immitis produces two unrelated heat-stable antigens which are diagnostically useful in immunodiffusion tests. One, the tube precipitin antigen, is valuable for specifically detecting antibody and diagnosing early primary cases of coccidioidomycosis. The other heat-stable antigen, designated HS, is the most useful coccidioidin antigen for specifically immunoidentifying C. immitis cultures. Both of the antigens were compared and evaluated for their usefulness in exoantigen and serologic immunodiffusion tests. Our studies indicated that the detection of tube precipitin antigen is of limited value for immunoidentifying C. immitis isolates because the antigen is common to certain gymnoascaceous saprophytes, such as Arachniotus, Auxarthron, and Malbranchea species, that form alternate arthroconidia. Antibodies to HS antigens are infrequently found in human sera from patients with coccidioidomycosis and are thus of little serodiagnostic value.