Serologic Studies on Antigens from Histoplasma Capsulatum Darling

The presence of precipitins in the sera of 19 experimentally infected rabbits was determined with four antigens prepared from the mycelial and yeastlike phases of H. capsulatum, namely, the ground-YP filtrate, the ground-mycelial filtrate, the YP broth filtrate, and the mycelial broth filtrate. Positive titers appeared approximately 13 days after infection, reached their peaks one week later, and finally disappeared about 10 weeks after infection. The binding power of seven antigens was compared by precipitative and complement-fixation technics, employing sera from animals experimentally infected with H. capsulatum. In the precipitin-tests and in complement-fixation tests with sera from hyperimmune rabbits, the mycelial broth filtrate displayed the greatest reactivity. However, in complement-fixation tests with sera from chronically infected rabbits only the three particulate antigens were active. Cross-absorption tests revealed that the seven antigens were divisible into two groups, both occurring within or on the cell, but only one in the culture-medium and ground-cell filtrates. Antigens elaborated by the mycelial phase and by the yeastlike phase were similar.