Millions of people harbor latent infections of the fungus Histoplasma capsulatum. Such persistent infections represent a stalemate between mechanisms of virulence and the immune response. The differing responses of inbred mouse strains to the same pathogen reflect variation in the genes that control the outcome of infection. Here we show that a 250-fold difference in H. capsulatum susceptibility between inbred mouse strains is attributable to the genotype at the MHC H2 locus. Gene expression analysis of strains varying only at the H2 locus identified genotype-specific and genotype-independent expression signatures, including infection-induced genes such as the fungal pattern recognition receptor Clec7a. Surprisingly, B-cell-specific gene expression was negatively correlated with fungal burden, whereas neutrophil-specific genes were correlated with superior disease outcome. Indeed, disease outcome improved when B cells were eliminated and neutrophils were more active, a previously unknown aspect of the host response. These data refine the understanding of genetic influences on histoplasmosis, reveal how shifts in the composition of immune cell populations compel different disease outcomes, and uncover how innate immunity modulation alters histoplasmosis.G enetic differences among individuals can have profound effects on infectious disease susceptibility and severity; for example, severe infections with the dimorphic fungal pathogen Coccidioides immitis are more frequent in males and people of African or Asian descent (1). This relationship inspires the hope that uncovering the pivotal genes affecting disease outcome might lead to new therapeutic strategies for controlling disease. For histoplasmosis, a fungal pneumonia affecting millions of people worldwide (2), infection outcomes vary greatly among mouse strains with only minor differences in cytokine profiles (3, 4). Although molecular ablation has connected an orderly and well-defined cytokine response to histoplasmosis outcome (5-7), previous mouse strain studies have highlighted the unexplained aspects of a successful immune response. The experiments reported herein identify a major influence of the H2 locus on experimental infections of mice with the fungal pathogen Histoplasma capsulatum, uncover gene expression signatures of neutrophils and B cells in resistant strains of mice, show that B cells impair the antifungal response, and implicate the innate immune system as an early control point.
ResultsGenetic Control of Disease Outcome After H. capsulatum Infection.We previously mapped quantitative trait loci controlling the phenotype of fungal burden using recombinant inbred mice (3). These data identify two regions on chromosome 17 linked to 250-fold lower fungal burden in the spleens of resistant A/J mice compared with sensitive C57BL/6 (B6) mice. One of those regions is tightly linked to the MHC H2, a highly variable multigene complex encoding the proteins responsible for antigen presentation. To test the contribution of the H2 locus to the immune respon...