Reactivity of alkali-soluble, water-soluble cell wall antigen of Coccidioides immitis with anti-Coccidioides immunoglobulin M precipitin antibody.

The alkali-soluble, water-soluble cell wall antigen of Coccidioides immitis (C-ASWS) mycelia and spherules was shown to react with anti-Coccidioides immunoglobulin M (IgM) precipitin antibody, both in the classical tube precipitin test and in the immunodiffusion assay for tube precipitin antibody (IDTP). The reactions obtained between C-ASWS and reference IgM precipitin antibody were identical to the reaction obtained when reference coccidioidin (CDN) was used. Definitive proof that C-ASWS extracts contain antigenic determinants that are reactive with IgM tube precipitin antibody was obtained by solid-phase immunoadsorption. Elution of reference IDTP antiserum over a column containing mycelium C-ASWS coupled to Sepharose 4B completely adsorbed precipitin antibody; i.e., reactivity in the IDTP was demonstrable in the column eluate but not in the column effluent fraction. The antigenic composition of C-ASWS extracts was evaluated and compared with that of CDN by two-dimensional immunoelectrophoresis against burro anti-CDN. The results established that both mycelium and spherule C-ASWS contain antigenic determinants in common with only one antigen present in CDN. The latter, designated antigen 2, is a large polymer which is predominant among the antigenic components in CDN. On a dry weight comparison, antigen 2 determinants were most concentrated in spherule C-ASWS, followed by mycelium C-ASWS and reference IDTP antigen. The finding that C-ASWS extracts are reactive with IgM tube precipitin antibody and are antigenically identical to antigen 2 in CDN suggests that antigen 2 is the biologically active component of CDN in tube precipitin assays.