Precipitin Reactions in Experimental Histoplasmosis and Blastomycosis

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Abstract
A report is given of the demonstration of precipitins in the sera of animals inoculated with either Histoplasma capsulatum or Blastomyces dermatitidis. One group of rabbits was inoculated with the yeastlike phase of H. capsulatum and the other with that of B. dermatitidis. Three normal rabbits were controls. All animals were bled prior to inoculation and at weekly or biweekly intervals thereafter, and their sera examined for precipitating antibodies. The antigens used were filtrates of broth cultures of the mycelial phase of these 2 organisms, and 4 fractions isolated from the filtrates of broth cultures of H. capsulatum. Histoplasmin was fractionated into 4 fractions. Fraction 1 was protein-like; fraction 2 was polysaccharide-like; the chem. nature of fraction 3 was uncertain; and fraction 4 was polysaccharide-like. Precipitins were demonstrated in the sera of the infected animals by the ''ring test.'' Histoplasmin, blasto-mycin, and fraction 1 gave positive precipitin tests with sera from both groups of rabbits and were considered nonspecific. Fractions 2 and 3 were mor specific for antibodies stimulated by H. capsulatum. Fraction 4 reacted in low dilution with 4 out of 7 sera from the H. capsulatum-inoculated rabbits but failed to react with sera from those inoculated with B. dermatitidis. The presence of antibodies against fractions 2, 3, and 4 was of short duration. Antibodies to histoplasmin and blastomycin could still be demonstrated 9 wks. after injn. Fractions 1 and 2 were not specific for H. capsulatum in 1:100 or 1:1 00 dilution. Fraction 3 gave negative results in a 1:1000 dilution. Fraction 4 in a 1:10 dilution gave positive reactions in rabbits injd. with H. capsulatum and negative results in animals injd. with B. dermatitidis. Fraction 4 is thus the most specific fraction. The 3 normal rabbits reacted negatively to all antigens injd. intradermally.

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