In vivo and in virto cellular responses to cytoplasmic and cell wall antigens of Histoplasma capsulatum in artificially immunized or infected guinea pigs

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Abstract
Guinea pigs were infected with different doses of yeasts of Histoplasma capsulatum or artifically immunized with several concentrations of unextracted yeast cell walls, and then tested in vivo and in vitro for cell-mediated responses to various subcellular fractions of the fungus. Three types of cell-mediated responses were measured, viz., skin test activity, production of migration inhibition factor, and lymphocyte transformation. Positive cutaneous reactions were elicited in animals immunized with 100 or 1,000 mug of cell walls when such animals were skin-tested with cell wall glycoprotein of soluble cytoplasmic substances, whereas animals immunized with 2,000 mug of cell walls did not react significantly greater than unsensitized animals when skin-tested with the same antigens. Histoplasmin did not elicit cutaneous sensitivity in guinea pigs infected with the smallest inoculum, 6 X 10(5) yeast cells, or in animals immunized with cell walls, regardless of the concentration of cell walls used as immunogen. However, hypersensitivity to H. capsulatum could be detected with cytoplasmic substances in animals infected with 6X 10(5). In guinea pigs infected with larger doses, i.e., 10 X 10(7), 15 X10(7), or 20 X 10(7), hypersensitivity could be detected with histoplasmin, cell wall glycoprotein, a ribosome-rich fraction, and soluble cytoplasmic substances. Both cell wall glycoprotein and soluble cytoplasmic substances were functional in migration inhibition factor assays with peritoneal exudate cells from animals immunized with 100 or 1,000 mug of cell walls. The transformation of lymphocytes from infected and artificially immunized guinea pigs in the presence of cell wall glycoprotein and soluble cytoplasmic substances was variable and unpredictable, the lymphocytes from some animls within a given group transforming and those from other animals showing no evidence of stimulation. Moreover, the level of stimulation could not be correlated with the degree of dermal hypersensitivity. These findings suggest that cell wall glycoprotein, and the fractions containing ribosomes and soluble cytoplasmic substances, could be useful antigens in assays for cellular immunity, and warrant further investigation with respect to specificity and active components.