Studies on Histoplasmosis

Abstract

Summary Results of two tests of experimental histoplasmosis in hamsters showed that infections induced by i.d. inoculation progressed to a somewhat slower, less extensive dissemination and to an earlier clearance of organisms from the tissue than infections induced by s.c. inoculation. The Histoplasma inhibitory factor (HIF) was demonstrated in 30% of the animals (66% of those infected more than one week) with infections of moderate intensity induced by i.d. inoculation of 10,000 yeast cells; whereas, in infections resulting in early and extensive dissemination, induced by either i.d. or s.c. inoculation of 50,000 Histoplasma yeast cells, little or no HIF was demonstrable. HIF activity could be demonstrated in portions of liver and in saline extracts of liver tested against in vitro grown organisms of the homologous and two heterologous strains of Histoplasma. No HIF activity was demonstrable against a variant strain derived from the homologous strain organism. Heated liver extracts, aqueous suspensions of alcohol soluble material and heated fractions thereof also exhibited HIF activity. No HIF activity could be detected against the mycelial form of Histoplasma in initial cultures of infected tissue or in tests using in vitro grown organisms. The inadequacies of the present methods of testing for HIF are discussed and suggestions are made for following the production of the inhibitor in the living animal.