Identification of the active precipitin components in a purified preparation of the A antigen of Blastomyces dermatitidis.

A purified A-antigen preparation of Blastomyces dermatitidis was determined to be composed of five major glycoprotein bands, visible with Coomassie blue and periodic acid-Schiff staining of polyacrylamide gels. At least 20 additional protein bands were detected by using a silver stain, which was 100 times more sensitive than the Coomassie method. Two components of this mixture were determined to be associated with the A-antigenic activity of B. dermatitidis. Of several antigen preparations examined in Ouchterlony precipitation tests, those reactive with a reference anti-A antiserum contained the slowest moving of the Coomassie blue bands. The antigen preparations without precipitin reactivity lacked this protein band. Two protein bands were shown to disappear from an antigen preparation after incubation with an affinity gel linked to the reference anti-A serum. One of the bands was the slowest Coomassie blue band, and the other was a fast-migrating protein detectable only with the silver stain. Characterization of the components responsible for the A-antigenic activity has important applications in the production and standardization of serological reagents for the diagnosis of blastomycosis.