Isolation of skin test-active preparations from yeast-phase cells of Blastomyces dermatitidis

Cell wall and cytoplasmic fractions were isolated from mechanically disrupted yeast-phase cells of Blastomyces dermatitidis in an effort to obtain a reliable skin-test antigen. The biological activities of these fractions were compared with those of two blastomycin preparations. The cytoplasmic antigens exhibited a low index of specificity yet exceeded the specificities of the blastomycins. The skin test-active component(s) of the cytoplasmic material had a molecular weight between 10,000 and 30,000 and could easily be concentrated by ultrafiltration on a PM-10 membrane. Unlike the cytoplasmic antigens and blastomycins, an alkali-soluble, water-soluble cell wall antigen effectively distinguished guinea pigs that were sensitized to B. dermatitidis from those sensitized to Histoplasma capsulatum. The biological activity of the yeast-phase antigen could be quantitated, on a weight basis, after purification by ultrafiltration (PM-10 membrane).