Comparison of immunoblot analyses of spherule-endospore-phase extracellular protein and mycelial-phase antigen of Coccidioides immitis

The extracellular proteins produced by Coccidioides immitis during growth of the spherule-endospore-phase and mycelial-phase antigen (coccidioidin) were studied by polyacrylamide gel electrophoresis followed by immunoblot analysis to detect specific serologic function. Filtrates obtained from 28- and 120-h growth of the spherule-endospore phase were compared with each other and with coccidioidin by using negative, immunoglobulin M (IgM) precipitin-positive, or complement fixation-positive pooled and single human sera followed by peroxidase-labeled anti-human IgA, IgE, IgG, or IgM (heavy chain specific) or peroxidase-labeled concanavalin A to detect the reaction. A total of 35 bands was seen in the stained gels. Different patterns were noted among the two spherule-endospore preparations and unheated and heated coccidioidin. At least 15 electrophoretically separate antigens were detected with positive serum ranging in approximate molecular weight (M(r)) from 100,000 to 18,000. Most were clustered between 45 and 60 kilodaltons (kDa). Common bands were noted at 48 and 18 kDa. At least one band at 48 kDa was strongly reactive with complement fixation-positive serum demonstrated by reaction with anti-IgG and anti-IgE. In contrast, doublet bands in the 50- to 65-kDa area were highly reactive with IgM precipitin-positive serum detected by anti-IgM. IgM antibodies present in both positive sera reacted with a band at 46 kDa which was not reactive with IgG. Heating the antigens altered the reactivity of many of the antigens, including the 48-kDa band, but not the 46-kDa band.