Submitted on September 21, 2007
Revised on February 28, 2008
HIV-1 Transgenic Expression in Rats Decreases Alveolar Macrophage Zinc Levels and Phagocytosis
Pratibha C Joshi1*, Robert Raynor1, Xian Fan1, and David M Guidot1
1 Department of Medicine, Atlanta VAMC and Emory University School of Medicine, Decatur, GA, USA
* To whom correspondence should be addressed. 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 GM-CSF, which is produced and secreted by the alveolar epithelium. Macrophages respond to GM-CSF through the GM-CSF receptor, which has a binding subunit (GM-CSFR
) and a signaling subunit (GM-CSFR
). In this study, we measured GM-CSF receptor expression and alveolar macrophage function in a transgenic 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-CSFR
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, TPEN, and this decreased GM-CSFR
expression and phagocytosis. In parallel, treatment with Zn acetate in vitro for 48h 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.