Antigenic Fractions Specific for Histoplasma capsulatum in the Complement Fixation Reaction

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Abstract
Cross reactions that occur among the spp. Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis have complicated the use of serological procedures for diagnosis. The objective of this study was to show whether it was possible to isolate an antigen specific for H. capsulatum from cultures of this organism. Such an antigen was isolated from the supernatant fluid of a yeast phase culture by precipitation with zinc acetate, followed by shaking an aqueous solution with chloroform and precipitation of the antigen with 5 volumes of ethanol. This antigen was tested by the complement fixation reaction using serums from rabbits infected with H. capsulatum. B. dermatitidis. or other pathogenic fungi. The antigen reacted with serum from each of the 6 Histoplasma-infected rabbits used but failed to cross react with other fungi. The antigens reacted with serum taken at intervals between 2 and 20 weeks post-infection. A further study with human serum is planned.
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