A CRITICAL ROLE OF NITRIC-OXIDE IN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE 1-INDUCED HYPERRESPONSIVENESS OF CULTURED MONOCYTES

Human immunodeficiency virus type 1 (HIV-1) infection leads to a gener al exhaustion of the immune system. Prior to this widespread decline o f immune functions, however, there is an evident hyperactivation of th e monocyte/macrophage arm. Increased levels of cytokines and other bio logically active molecules produced by activated monocytes may contrib ute to the pathogenesis of HIV disease both by activating expression o f HIV-1 provirus and by direct effects on cytokine-sensitive tissues, such as lung or brain. In this article, we investigate mechanisms of h yperresponsiveness of HIV-infected monocytes. Materials and Methods: T he study was performed on monocyte cultures infected in vitro with a m onocyte tropic strain HIV-1(ADA). Cytokine production was induced by s timulation of cultures with lipopolysaccharides (LPS) and measured by ELISA. To study involvement of nitric oxide (NO) in the regulation of cytokine expression, inhibitors of nitric oxide synthase (NOS) or chem ical donors of NO were used. Results: We demonstrate that infection wi th HIV-1 in vitro primes human monocytes for subsequent activation wit h LPS, resulting in increased production of proinflammatory cytokines tumor necrosis factor (TNF) and interleukin 6 (IL-6). This priming eff ect can be blocked by Ca2+-chelating agents and by the NOS inhibitor L -NMMA, but not by hemoglobin. It could be reproduced on uninfected mon ocyte cultures by using donors of NO, but not cGMP, together with LPS. Conclusions: NO, which is expressed in HIV-1-infected monocyte cultur es, induces hyperresponsiveness of monocytes by synergizing with calci um signals activated in response to LPS stimulation. This activation i s cGMP independent. Our findings demonstrate the critical role of NO i n HIV-1-specific hyperactivation of monocytes.