Histoplasmosis in purebred mice: influence of genetic susceptibility and immune depression on treatment

Invasive models of histoplasmosis

Histoplasmosis results from infection with the fungal organism Histoplasma capsulatum. Most Histoplasma research today uses models based on primary pulmonary infection. Following inhalation, conidia are rapidly ingested and intracellularly convert to the yeast form. After initial pulmonary infection, organisms are carried throughout the body giving rise to disseminated infection. Three murine infection models have been developed which mimic human disease. These comprise models of primary infection following initial exposure to the organism, secondary exposure to Histoplasma following spontaneous recovery from primary disease and a model of reactivated infection following spontaneous clearance of primary disease. This chapter describes these models and explores variability introduced with the use of mice of varied genetic backgrounds and different H. capsulatum strains.

Genetic control of susceptibility to Cryptococcus neoformans in mice

Inbred mice injected intravenously with 5 x 10(6) cells of Cryptococcus neoformans showed two patterns of survival: sensitive (A/WySn, A.BY, A/J, DBA/2J, NZB/B1NJ, and SWR/J) and resistant [C57BL/10Sn, B10.A, B10.A (2R), B10.S (7R),C57BR/cdJ, C58/J, C3H/HeJ, BALB/c, DBA/1J, and SJL/J]. Relative susceptibility based on survival time was shown to correspond to differences obtained for 50% lethal dose values. Either decreasing the dose of organisms or changing to the intraperitoneal route of inoculation resulted in prolonged survival times, but neither change affected the observed patterns of survival. F1 hybrids between different sensitive strains were also sensitive, whereas F1 hybrids between sensitive and resistant strains were resistant, indicating a dominant mode of inheritance. Sensitivity and resistance were shown to be under single gene control by segregation analysis in F2 progeny produced by inbreeding (B10.A x A/WySn)F1 hybrids and in (F1 x A/WySn) backcross progeny. Blood obtained from parental strains, F1, F2, and backcross hybrids was tested for the presence or absence of hemolytic complement. Mice lacking hemolytic complement activity in their sera are homozygous for the Hc(0) allele at the Hc locus on chromosome 2 and are deficient in the complement component C5. A 1:1 correspondence was found between C5 deficiency and sensitivity to C. neoformans. Resistance was shown to cosegregate with the presence of hemolytic complement in the F2 and the backcross progenies.