Characterization of antigens from the yeast phase of Histoplasma capsulatum

Preliminary studies established methods for obtaining maximum yields of viable cells. Liquid shaken cultures of Histoplasma capsulatum provided a maximum of 4 x 10(8) to 5 x 10(8) cells/ml regardless of the inoculum size. Under optimum conditions, cells were viable (90 to 95%) for 168 to 240 hr. Generation times ranged from 7.52 to 8.36 hr. Immunodiffusion, immunoelectrophoresis, and ultracentrifugation studies on phenol and ethylenediamine extracts of intact cells and cell walls revealed the presence of two components in the ethylenediamine extracts and three in the phenol preparations. The ethylenediamine extracts from intact cells and cell walls seemed to be identical although one of the components was more abundant in cell walls. Mice injected intraperitoneally with intact cells or cell walls were protected against intravenous challenge with H. capsulatum. Among the extracts, the water-soluble ethylenediamine extract from cell walls was most immunogenic. The other extracts gave only a light protection or none at all. Intact cells and cell walls were slightly toxic to mice. Two of the extracts were toxic when incorporated into Freund's complete adjuvant.