Cellular immune activity of a galactomannan-protein complex from mycelia of Histoplasma capsulatum.

A galactomannan-protein complex was extracted from defatted mycelium of Histoplasma capsulatum with 0.25 N alkali at 25 C. It accounted for 7.5% of the cell dry weight in nondialyzable form and had a galactose-mannose ratio of 2:5. The complex containing 68% protein was separated into polysaccharide and glycoprotein components by ion-exchange chromatography. The galactomannan formed a single precipitate in immunodiffusion, sharing a common antigen with the glycoprotein which contained two precipitating antigens. The glycoprotein elicited delayed-type hypersensitivity in guinea pigs as measured by skin-test and macrophage migration inhibitory factor assay, with 5 mug resulting in 86% specific inhibition. The galactomannan was skin-test negative, but 10 mug resulted in 80% specific inhibition of migration.