Nitric oxide regulates MIP-1 alpha expression in primary macrophages and Tlymphocytes: Implications for anti-HIV-1 response

Background: Chemokines and chemokine receptors have been shown to play a cr itical role in HIV infection. Chemokine receptors have been identified as c oreceptors for viral entry into susceptible target cells, and several membe rs of the beta chemokine subfamily of cytokines, MIP-1 alpha, MIP-1 beta, a nd RANTES, have been identified as the major human immunodeficiency virus ( HIV)-suppressive factors produced by activated CD8+ T lymphocytes. In macro phages, HIV-1 infection itself was shown to upregulate the production of MI P-1 alpha and MIP-1 beta. In the present study, we address the mechanisms b y which HIV-1 infection regulates beta chemokine responses in macrophages a nd lymphocytes. Material and Methods: To address whether nitric oxide (NO), generated as a consequence of HIV-1 infection, regulates beta chemokine responses in monoc yte/macrophages and/or macrophage-depleted peripheral blood mononuclear cel ls (PBMCs) these two cell populations were isolated from HIV seronegative d onors, placed in culture, and infected with HIV-1 in either the presence or absence of exogenous activators (e.g. lipopolysaccharide, phytohemagglutin in), inhibitors of nitric oxide synthase (NOS), or chemical donors of NO. C ultures were analyzed for beta chemokine responses by ELISA and RNase prote ction. Results: LPS-induced MIP-1 alpha release is enhanced in HIV-1-infected, as compared to uninfected, monocyte/macrophage cultures, and this enhancing ef fect is partially blocked by the addition of inhibitors of NOS, and can be reproduced by chemical generators of NO even in the absence of HIV-1 infect ion. A similar strategy was used to demonstrate a role for NO in HIV-1-medi ated induction of MIP-1 alpha in unstimulated macrophage cultures. NOS inhi bitors also decreased MIP-1 alpha and MIP-1 beta production by phytohemaggl utinin-stimulated monocyte-depleted PBMC cultures. Conclusions: These results indicate that NO amplifies MIP-1 alpha responses in activated macrophages and lymphocytes, and suggests that this pleiotrop ic molecule might function as an enhancing signal that regulates secretion of beta chemokines during HIV-1 infection. These findings reveal a novel me chanism by which NO might regulate the anti-HIV activity of immune cells.