Control of the Host Response to Histoplasma Capsulatum
The mammalian host response to fungal pathogens is complex and varies with the different species in part as a result of differences in biochemical and genetic composition, portals of entry, and morphology. Among the fungal pathogens, Histoplasma capsulatum is one of the few that behaves both as a primary pathogen and as an opportunist, i.e., causes serious life-threatening infection in both immunocompetent and immunocompromised hosts. This fungus is found in the soil in many continents but does manifest a geographic restriction. The highly endemic areas are the midwestern and southeastern regions of the United States and large segments of Central and South America. The portal of entry for this fungus is the lungs. Infection of mammals is coincidental with the disruption of the soil. Most infections resolve spontaneously although the organism establishes a dormant state. Numerous mediators and cell populations must cooperate to effect a successful resolution of infection. Primary among them are T cells, macrophages, tumor necrosis factor-α and interferon-γ. However, these constituents constitute only a fraction of the mediators and cells that contribute to host regulation of invasion. The chapter herein will explore the elements of the immune response and how each contributes to regulation. We also will endeavor to define intersections among cell populations and soluble mediators.
KeywordsNitric Oxide Dendritic Cell Yeast Cell Programme Death Ligand Fungal Burden
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