Metallomic Analysis of Macrophages Infected withHistoplasma capsulatumReveals a Fundamental Role for Zinc in Host Defenses

The fungal pathogen Histoplasma capsulatum evades the innate and adaptive immune responses and thrives within resting macrophages. Cytokines that induce antimicrobial activity, such as granulocyte macrophage colony-stimulating factor (GM-CSF), inhibit H. capsulatum growth in macrophages. Conversely, interleukin 4 inhibits the killing of intracellular pathogens. Using inductively coupled plasma mass spectrometry, we examined alterations in the metal homeostasis of murine H. capsulatum-infected macrophages that were exposed to activating cytokines. Decreases in the levels of iron (Fe(2+) and Fe(3+)) and zinc (Zn(2+)) were observed in infected, GM-CSF-treated macrophages compared with those in infected controls. Interleukin 4 reversed the antifungal activity of GM-CSF-activated macrophages and was associated with increased intracellular Zn(2+) levels. Chelation of Zn(2+) inhibited yeast replication in both the absence of macrophages and the presence of macrophages. Treatment of cells with GM-CSF altered the host Zn(2+) binding species profile. These results establish that Zn(2+) deprivation may be a host defense mechanism utilized by macrophages.