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

Abstract

The fungal pathogen Histoplasma capsulatum evades the innate and adaptive immune responses and thrives within resting macrophages (Mφ). Cytokines that induce antimicrobial activity such as granulocyte macrophage-colony stimulating factor (GM-CSF) inhibit H. capsulatum growth in Mφ. Conversely, interleukin 4 (IL-4) inhibits the killing of intracellular pathogens. Using inductively coupled plasma mass spectrometry, we examined alterations in metal homeostasis of murine H. capsulatum-infected Mφ infected that were exposed to activating cytokines. Restriction of iron (Fe2+/3+) and zinc (Zn2+) was observed in infected, GM-CSF-treated Mφ compared to infected controls. IL-4 reversed the anti-fungal activity of GM-CSF-activated Mφ and was associated with increased intracellular Zn2+. Chelation of Zn2+ inhibited yeast replication both in the absence and presence of Mφ. Treatment of cells with GM-CSF altered the host Zn2+ binding species profile. These results establish that Zn2+ deprivation may be a host defense mechanism utilized by Mφ.

Adaptive Immunity to Fungi

“…Both IL-4 and IL-13 drive alternative activation of macrophages that is associated with uncontrolled fungal growth. C. neoformans and H. capsulatum proliferate robustly in macrophages primed with IL-4, as opposed to the ones that are classically activated (Voelz et al 2009;Winters et al 2010). These alternatively activated phagocytes display amplified levels of arginase-1, an enzyme that potentially diminishes the amount of nitric oxide required for fungicidal activity .…”

“…This phenomenon is believed to augment fungal growth within the cells. In addition, IL-4 alters intracellular survival by increasing zinc content that supports the growth of fungal pathogens (Winters et al 2010).…”

Differentiation of the fungus Histoplasma capsulatum into a pathogen of phagocytes

“…Zinc is essential for Histoplasma yeast proliferation in vitro as well as in macrophages [36]. GM-CSF treatment of macrophages increases total cellular zinc, but it also impairs Histoplasma zinc assimilation [37**].…”

Histoplasma Capsulatum , Lung Infection and Immunity

“…Both human and murine macrophages activated with GM-CSF upregulate metallothioneins, small metal-binding proteins which reduce intracellular free zinc [34, 68]. Metallothionein-driven reduction of zinc supports production of ROS by increasing activity of the phagosomal H + channel [34].…”

“…Thus, GM-CSF’s ability to inhibit yeast growth in macrophages may be due to zinc deprivation and enhanced ROS. In contrast to GM-CSF, IL-4 increases zinc availability to intracellular yeast [68]. …”