Identification and characterization of an immunodominant 58-kilodalton antigen of Aspergillus fumigatus recognized by sera of patients with invasive aspergillosis

Abstract

Sera from 38 patients with invasive aspergillosis were tested by Western immunoblotting for the presence of antibodies to antigens of Aspergillus fumigatus present in a mycelial extract of the organism. All of the sera contained antibodies to an antigen of molecular weight 58,000, which was which was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was the only antigen recognized in approximately 90% of the sera tested. The 58-kDa antigen is an abundant component of mycelial extracts composing approximately 50% of the Coomassie blue-stained protein. The antigen also contains carbohydrate, since it is stained by the carbohydrate stain periodic acid-Schiff and it binds to the lectin concanavalin A. It was purified by immunoaffinity chromatography employing a monoclonal antibody directed against an epitope on the 58-kDa antigen. Analysis of the purified antigen by gas-liquid chromatography revealed the presence of mannose, galactose, and glucose residues in a 2:1:2 ratio. The ratio of protein to carbohydrate is 1.16:1. The protein is slightly acidic, containing relatively high quantities of glutamic and aspartic acids, glycine, alanine, serine, and threonine. The 58-kDa antigen also contains phosphate groups as part of its structure. Serological activity was totally destroyed after treatment with sodium metaperiodate and was partially destroyed after treatment with pronase. The 58-kDa antigen was not able to hydrolyze protein.