Neopterin production by HIV-1-infected mononuclear phagocytes

Neopterin is a pteridine produced by human mononuclear phagocytes, usually in response to interferon-gamma (IFN-gamma) stimulation. Increasing serum levels of neopterin correlate with clinical progression to AIDS in HIV-infected people, but the factors that contribute to these elevated levels are not established. We performed in vitro experiments to investigate the possibility that HIV-1 infection of mononuclear phagocytes directly induces enhanced neopterin production. We found that HIV-1-infected monocytes and peritoneal macrophages produced neopterin in quantities similar to amounts produced by uninfected cells. The HIV-infected cells responded to stimulation with IFN-gamma as well as uninfected cells, with a 6- to 12-fold increase in neopterin production. We conclude that elevated serum levels of neopterin in HIV-infected individuals are not caused by HIV-1 infection of mononuclear phagocytes but may be a result of the normal response to mononuclear phagocytes to increased levels of IFN-gamma.