Inhibition of HIV Replication and Macrophage Colony-Stimulating Factor Production in Human Macrophages by Antiretroviral Agents

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Abstract
Macrophage colony-stimulating factor (M-CSF) enhances the susceptibility of macrophages to infection with HIV-1, in part by increasing the expression of CD4 and CCR5. Human monocyte-derived macrophages (MDMs) infected in vitro with HIV-1 endogenously produce M-CSF, with kinetics paralleling virus replication, which can lead to enhanced spreading of the infection. AZT and ritonavir both inhibit HIV replication, but their impact on M-CSF production by HIV-infected human MDMs is unknown. The dose response and kinetics of virus replication in the presence of AZT and ritonavir were determined for HIV-infected MDMs from HIV-seronegative donors. Harvested supernatants were monitored for reverse transcriptase activity, M-CSF production, and HIV proteins. Our data suggest that threshold levels of HIV replication must occur before maximum M-CSF production is induced. Addition of AZT or ritonavir before or after establishment of productive HIV infection dramatically reduces virus replication and M-CSF production by human MDMs. However, ongoing virus replication and M-CSF production are slow to return to baseline levels after addition of AZT or ritonavir, suggesting that HIV replication and virion release from infected macrophages continue long after initiation of antiretroviral therapy. Our results suggest that, in human macrophages, HIV-1 replication and M-CSF production are inextricably linked, such that inhibition of one leads to a concomitant reduction of the other. Low-level HIV replication and M-CSF release during ongoing antiretroviral therapies may facilitate the survival and maintenance of infected macrophages and suggests that additional therapies targeting M-CSF may be critical for elimination of macrophage reservoirs.

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