Productive infection of plasmacytoid dendritic cells with human immunodeficiency virus type 1 is triggered by CD40 ligation

Immature plasmacytoid dendritic cells are the principal alpha interferon-producing cells (IPC), responsible for primary antiviral immunity. IPC express surface molecules CD4, CCR5, and CXCR4, which are known coreceptors required for human immunodeficiency virus (HIV) infection. Here we show that IPC are susceptible to and replicate HIV type 1 (HIV-1). Importantly, viral replication is triggered upon activation of IPC with CD40 ligand, a signal physiologically delivered by CD4 T cells. Immunohistochemical staining of tonsil from HIV-infected individuals reveals HIV p24(+) IPC, consistent with in vivo infection of these cells. IPC exposed in vitro to HIV produce alpha interferon, which partially inhibits viral replication. Nevertheless, IPC efficiently transmit HIV-1 to CD4 T-cells, and such transmission is also augmented by CD40 ligand activation. IPC produce RANTES/CCL5 and MIP-1alpha/CCL3 when exposed to HIV in vitro. IPC also induce naive CD4 T cells to proliferate and would therefore preferentially infect these cells. These results indicate that IPC may play an important role in the dissemination of HIV.