Antigenemia in rabbits infected with Candida albicans serotype B: detection by enzyme immunoassay and preliminary characterization of the antigen

Abstract

Peroxidase-labeled IgG against Candida albicans serotype A cell walls failed to detect antigenemia in rabbits infected with C. albicans type B. Therefore type B antisera were produced in rabbits immunized with either type B cell walls; whole blastoconidia heated and killed at 60 degrees C (HK); a sublethal intravenous dosage of 10(6) colony forming units (c.f.u.); or a normally lethal dose of 10(7) c.f.u. injected into subcutaneously implanted plastic chambers. The four antisera were conjugated to peroxidase for a double antibody sandwich enzyme immunoassay. Sixteen rabbits, immunosuppressed with cortisone, received 10(7) type B blastoconidia intravenously. On day 4 their kidneys contained between 3.4 X 10(8) and 1.4 X 10(11) c.f.u. Antigenemia was detected only with the conjugated anti-HK-IgG. A mean concentration of 246 ng ml-1 of circulating antigen was detected only when serum-antigen complexes were dissociated by boiling in EDTA. The properties of the circulating antigen were as follows: relative molecular weight between 50 000 and 100 000 da; stable to boiling and proteinases, labile to sodium periodate oxidation, and bound by concanavalin A. These properties are consistent with a polysaccharide or glycoprotein, probably the mannoprotein of the cell wall. Antigenic specificity was probed further using IgG produced against heat-killed C. albicans serotype A. Antigenemia resulting from infection with serotype B was detected in 5 of 5 rabbits tested with the anti-HK-serotype B IgG but only with 3 of 5 tested with the anti-HK-serotype A IgG. In addition, the concentrations detected with serotype B reagents were 31 times higher.