Demonstration of antigenemia by radioimmunoassay in rabbits experimentally infected with Aspergillus

Abstract

Antigens were detected in the blood of rabbits infected with Aspergillus fumigatus by a solid-phase (tube) radioimmunoassay (RIA). The radiolabel for the assay was a polysaccharide-rich alkali extract (APAE) from the mycelia of A. fumigatus. Before this extract could be suitable labeled with 125I, it had to be conjugated with tyramine. Rabbits immunized with heat-killed mycelia had titers of antibody in serum of as high as 1:38,000 against this radiolabeled antigen. With unlabeled and unconjugated APAE as the standard antigen, the sensitivity of the RIA was 12 ng per test, or 500 ng/ml. Antigenemia was detectable by RIA three days after infection of rabbits with A. fumigatus. Blood cultures taken concomitantly were uniformly negative. These results indicate that antigenemia occurs in invasive aspergillus infection and in such cases can be detected by RIA. These observations may be important in the diagnosis of invasive aspergillus infections in humans.