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HIV-1–Transgene Expression in Rats Decreases Alveolar Macrophage Zinc Levels and Phagocytosis

¹ Department of Medicine, Atlanta Veterans Affairs Medical Center, and Emory University School of Medicine, Atlanta, Georgia

Correspondence and requests for reprints should be addressed to Pratibha C. Joshi, Ph.D., Atlanta VAMC (151-P), 1670 Clairmont Road, Decatur, GA 30033. E-mail: pcjoshi{at}emory.edu

HIV-1 infection impairs alveolar macrophage immune function and renders patients susceptible to pneumonia by poorly understood mechanisms. Alveolar macrophage maturation and function depends on granulocyte-macrophage colony–stimulating factor (GM-CSF), which is produced and secreted by the alveolar epithelium. Macrophages respond to GM-CSF through the GM-CSF receptor (GM-CSFR), which has a binding subunit (GM-CSFR) and a signaling subunit (GM-CSFRβ). In this study, we measured GM-CSFR expression and alveolar macrophage function in a transgene HIV-1 rat model (NL4-3 gag/pol); this construct bears a pro-virus with gag and pol deleted, but other HIV-1–related proteins, such as gp120 and Tat, are expressed, and the rats develop an AIDS-like phenotype as they age. We first determined that HIV-1–transgenic expression selectively decreased alveolar macrophage expression of GM-CSFRβ and impaired bacterial phagocytosis in vitro. Next, we examined the role of zinc (Zn) deficiency as a potential mechanism underlying these effects, and determined that HIV-1–transgenic rats have significantly lower levels of Zn in the alveolar space and macrophages. To test the direct effect of Zn deficiency on macrophage dysfunction, we treated rat alveolar macrophage cell line with a Zn chelator, N,N,N',N'-tetrakis-(2-pyridyl-methyl) ethylenediamine, and this decreased GM-CSFRβ expression and phagocytosis. In parallel, treatment with Zn acetate in vitro for 48 hours restored intracellular Zn levels and phagocytic function in alveolar macrophages from HIV-1–transgenic rats. Taken together, these data suggest that pulmonary Zn deficiency could be one of the mechanisms by which chronic HIV-1 infection impairs alveolar macrophage immune function and renders these individuals susceptible to serious lung infections.

Key Words: AIDS • lung • monocyte/macrophages • phagocytosis • rodent

CLINICAL RELEVANCE This study demonstrates that pulmonary zinc status may be important in HIV-1 infection, and that pulmonary zinc deficiency could be one of the mechanisms by which HIV-1 infection impairs alveolar macrophage immune function.