Production of Interferon α by Human Immunodeficiency Virus Type 1 in Human Plasmacytoid Dendritic Cells Is Dependent on Induction of Autophagy

Background. The mechanisms responsible for interferon alpha (IFN-alpha) production by plasmacytoid dendritic cells (pDCs) during human immunodeficiency virus type 1 (HIV-1) infection are unknown. This research examined the roles of Toll- like receptor 7 (TLR7) and autophagy in IFN- a production by pDCs during HIV-1 infection. Methods. pDCs from human peripheral blood mononuclear cells were incubated with infectious or aldrithiol 2 (AT-2)-inactivated HIV-1 or with uridine-rich single-stranded RNA40 (ssRNA40) from the HIV-1 long terminal repeat. IFN-alpha was quantified by enzyme-linked immunosorbant assay. Autophagic proteins were detected by Western blot, and autophagosomes were identified using immunofluorescent and confocal microscopy. To inhibit autophagy, pDCs were treated with the phosphoinositide-3 kinase inhibitor 3-methyladenine (3-MA) or were transfected with autophagy-related protein 7 or TLR7 small interfering RNA (siRNA). Results. Increased levels of IFN-alpha were present in culture supernatants following 16-hour incubation of pDCs with infectious or AT-2-inactivated HIV-1. Treatment of pDCs with ssRNA40 but not ssRNA41 resulted in high levels of IFN-alpha. pDCs exposed to HIV-1 gp120, rapamycin, or 3-MA alone failed to induce IFN-alpha. Pretreatment of pDCs with 3-MA significantly reduced the induction of IFN-alpha by ssRNA40. Similarly, knock down of autophagy-related protein 7 and TLR7 by use of siRNA significantly reduced the induction of IFN-alpha by ssRNA40 or HIV-1. Conclusions. These findings demonstrate that IFN-alpha production by pDCs exposed to infectious or noninfectious HIV-1 and ssRNA40 occurs through induction of autophagy following TLR7 signaling.