The role of natural killer cells in histoplasmosis

The natural killer (NK) cell has been suggested as an early defense mechanism against Histoplasma capsulatum. Homozygous bg/bg mice, heterozygous bg/+ mice, and bg/+ mice treated with anti-asialo GM1 (ASGM1) were used to assess this postulated role. NK cell assays demonstrated that ASGM1 was effective in reduction of NK cell activity in bg/+ mice to levels comparable to bg/bg mice. To test for possible cross reaction with other immune cells and ASGM1, we evaluated lymphocyte and macrophage function. These studies included lymphocyte transformation, delayed-type hypersensitivity (DTH), and macrophage candidacidal activity. We found no evidence of any effects from ASGM1. Mice were evaluated for survival and colony counts after intravenous (i.v.) H. capsulatum challenge. We again confirmed increased susceptibility of bg/bg mice to H. capsulatum, but found no significant differences between bg/+ mice and bg/+ mice treated with ASGM1. Therefore, we conclude that NK cells play no major role in nonspecific early host defenses against H. capsulatum.