Analysis of a solid-phase radioimmunoassay for antibodies to cytoplasmic antigen fractions of Candida albicans.

An indirect solid-phase radioimmunoassay (SPRIA) in individual polystyrene microtiter cups has been adapted for measurement of antibody to various cytoplasmic and carbohydrate antigen fractions of Candida albicans. The assay was optimized for sensitivity, precision and linearization of serum dilution curves. The optimized procedure allows computerized measurement of anti-Candida antibodies and can be used for measurement of antibody over a wide concentration range. The procedure obviates variation due to changes in day-to-day counts as a result of isotope decay and end-point antibody dilutions. The assay has been used to demonstrate a Poisson-like distribution of antibody levels in the sera of persons showing no symptoms of candidiasis. The minimum antibody level detectable by the assay is about two orders of magnitude lower than the lowest level found in human serum and 4 orders of magnitude lower than the most sensitive test used hitherto, the hemagglutination test.