Histoplasma capsulatum infection in nude mice

D M Williams, J R Graybill, D J Drutz
1978 Infection and Immunity  
Congenitally athymic nude (nu/nu) mice, when injected intraperitoneally with Histoplasma capsulatum, developed a rapidly fatal disseminated infection characterized by heavy parasitization of reticuloendothelial tissues. In contrast, their heterozygous (nu/X) littermates, which possessed a functioning thymus, developed only a low-grade infection which was apparently self-limited and rarely fatal. Transplantation of thymic tissue into nu/nu mice diminished greatly the severity of infection and
more » ... of infection and reduced mortality by about 50%. These studies emphasize the importance of cell-mediated immunity in host defense against histoplasmosis and suggest that the nude mouse may be a valuable model for the study of this chronic intracellular infection. Although there have been a number of studies of histoplasmosis in humans and in experimental animals, the mechanism of host defense against Histoplasma capsulatum is not fully understood. Host defense is thought to depend primarily on cell-mediated immunity (CMI). The rationale for this is based largely on the association of histoplasma exposure with both a positive skin test and positive in vitro parameters of CMI (lymphocyte blastogenesis; production of migration inhibition factor (6, 10). These parameters often revert to negative in people with disseminated histoplasmosis (17, 25). Control of histoplasmosis is apparently achieved through T-lymphocyte intervention, which leads to macrophage activation (13-15). However, there are many unanswered questions concerning the character and specificity of cell-mediated immune processes and the role of antibody in host defense in histoplasmosis (8, 10, 17, 19, 25) . The congenitally athymic nude (nu/nu) mouse is known to have deficient CMI and impaired T-lymphocyte-dependent antibody production (22) . The present studies were designed to test the suitability of the nude mouse as a model for disseminated histoplasmosis, to compare its susceptibility to that of heterozgous (nu/X) littermates, and to evaluate the effect of thymus transplantation upon the course of infection. MATERIALS AND METHODS Mice. Specific-pathogen-free nude mice (nu/nu) on a BALB/c background were obtained from Sprague-Dawley, Inc. (Madison, Wis.) and maintained in the specific-pathogen-free state by using sterilized food, bedding, water, and barrier filter top cages. Breeding was performed by mating hairless nu/nu males with hairy female heterozygote (nu/X) littermates. Nude animals were checked periodically at autopsy to verify the absence of a developed thymus. Immunodeficiency was further confirmed by the inability of the nu/nu mice to reject homozygous (C1D H-2C) skin grafts and by their inordinate susceptibility to cryptococcosis (J. R. Graybill and D. J. Drutz, Cell. Immunol., in press). BALB/c mice without the nu gene were obtained from Charles River Laboratories (Wilmington, Mass.), since the original BALB/c strain from which the Sprague-Dawley nude mice were derived is not available in this country (Carl Hansen, personal communication). In the experiments to be described, 5to 7week-old animals of both sexes were used. H. capsulaturm Three strains of H. capsulatum were obtained. Strains 1077 and 102 were gifts of Rebecca Cox (San Antonio State Chest Hospital), and strain 877 was a clinical isolate. The identity of the fungi as H. capsulatum was confirmed by morphology and growth characteristics of mycelial and yeast-phase organisms. Strain 1077 was passed by the intraperitoneal route in nu/nu mice with periodic subculture on sheep blood agar. At 370C it grew as the yeast form. In one experiment, an inoculum which had only partially converted from mycelial to yeast form and which contained both budding yeast cells and hyphae in the process of conversion was used with equivalent results. Subsequently, this strain was maintained in the yeast form. Strains 877 and 102 were grown on brain heart infusion medium (Baltimore Biological Laboratory, Cockeysville, Md.) and maintained in the yeast form by serial passage on brain heart infusion slants at 370C. Infective inocula were prepared by diluting yeast or a mixture of hyphal and yeast-form H. capsulatum in phosphate-buffered saline and adjusting the number of organisms to 105 to 108/ml in a hemocytometer. The viability of yeast-phase organisms was approximately 20%. Infection was produced by intraperitoneal injection of 0.2 ml in each mouse. Animals were followed 973 on May 9, 2020 by guest http://iai.asm.org/ Downloaded from
doi:10.1128/iai.21.3.973-977.1978 fatcat:64jtcdd22rbjrc4p2gcxrgd7ia