Quantitation of antibody against cell wall mannan and a major cytoplasmic antigen of Candida in rabbits, mice, and humans.

Cell wall mannan of type A Candida albicans was purified, conjugated with tyramine, and labeled with 125I. Labeled cell wall mannan was used in a radioimmunoassay to measure serum antimannan antibody levels. An ammonium sulfate-soluble fraction of a cytoplasmic extract of C. albicans contained a large amount of a major cytoplasmic antigen of this organism. When the sulfate-soluble fraction was labeled with 125I, much more 125I attached to this major antigen than to the other antigens present in the sulfate-soluble fraction. Thus, when serum antisulfate-soluble fraction antibody levels were measured by a radioimmunoassay which used the iodine-labeled sulfate-soluble fraction, antibody against this major cytoplasmic antigen was quantitated. Both radioimmunoassays were used to measure antimannan and antisulfate-soluble fraction antibody levels in mice, rabbits, and humans. Irrespective of the procedure used to elicit antibody against C. albicans antigens, mice failed to produce antimannan antibody. By contrast, all strains of mice tested produced antisulfate-soluble fraction antibody after immunization, and the magnitude of this antibody response depended on the strain of mice immunized. Rabbits readily produced antibody against both mannan and sulfate-soluble fraction when immunized by a variety of methods. Antimannan antibody was detected in 100% of sera from a randomly selected sample of 50 hospitalized patients. Only 1 of 50 patients had antisulfate-soluble fraction antibody detectable by radioimmunoassay. In pooled normal human serum, most antimannan antibody was of the immunoglobulin G class.