Macrophages are key target cells for HIV-1. HIV-1_BaL induced a subset of interferon-stimulated genes in monocyte-derived macrophages (MDMs), which differed from that in monocyte-derived dendritic cells and CD4 T cells, without inducing any interferons. Inhibition of type I interferon induction was mediated by HIV-1 inhibition of interferon-regulated factor (IRF3) nuclear translocation. In MDMs, viperin was the most up-regulated interferon-stimulated genes, and it significantly inhibited HIV-1 production. HIV-1 infection disrupted lipid rafts via viperin induction and redistributed viperin to CD81 compartments, the site of HIV-1 egress by budding in MDMs. Exogenous farnesol, which enhances membrane protein prenylation, reversed viperin-mediated inhibition of HIV-1 production. Mutagenesis analysis in transfected cell lines showed that the internal S-adenosyl methionine domains of viperin were essential for its antiviral activity. Thus viperin may contribute to persistent noncytopathic HIV-1 infection of macrophages and possibly to biologic differences with HIV-1–infected T cells.

Langerhans cells (LC) are thought to be the only mononuclear phagocyte population in the epidermis where they detect pathogens. Here, we show that CD11c⁺ dendritic cells (DCs) are also present. These cells are transcriptionally similar to dermal cDC2 but are more efficient antigen-presenting cells. Compared to LCs, epidermal CD11c⁺ DCs are enriched in anogenital tissues where they preferentially interact with HIV, express the higher levels of HIV entry receptor CCR5, support the higher levels of HIV uptake and replication and are more efficient at transmitting the virus to CD4 T cells. Importantly, these findings are observed using both a lab-adapted and transmitted/founder strain of HIV. We also describe a CD33^low cell population, which is transcriptionally similar to LCs but does not appear to function as antigen-presenting cells or acts as HIV target cells. Our findings reveal that epidermal DCs in anogenital tissues potentially play a key role in sexual transmission of HIV.

Many viruses have developed mechanisms to evade the IFN response. Here, HIV-1 was shown to induce a distinct subset of IFN-stimulated genes (ISGs) in monocyte-derived dendritic cells (DCs), without detectable type I or II IFN. These ISGs all contained an IFN regulatory factor 1 (IRF-1) binding site in their promoters, and their expression was shown to be driven by IRF-1, indicating this subset was induced directly by viral infection by IRF-1. IRF-1 and -7 protein expression was enriched in HIV p24 antigen-positive DCs. A HIV deletion mutant with the IRF-1 binding site deleted from the long terminal repeat showed reduced growth kinetics. Early and persistent induction of IRF-1 was coupled with sequential transient up-regulation of its 2 inhibitors, IRF-8, followed by IRF-2, suggesting a mechanism for IFN inhibition. HIV-1 mutants with Vpr deleted induced IFN, showing that Vpr is inhibitory. However, HIV IFN inhibition was mediated by failure of IRF-3 activation rather than by its degradation, as in T cells. In contrast, herpes simplex virus type 2 markedly induced IFNβ and a broader range of ISGs to higher levels, supporting the hypothesis that HIV-1 specifically manipulates the induction of IFN and ISGs to enhance its noncytopathic replication in DCs.

Dendritic cells (DCs) and macrophages are present in the tissues of the anogenital tract, where HIV-1 transmission occurs in almost all cases. These cells are both target cells for HIV-1 and represent the first opportunity for the virus to interfere with innate recognition. Previously we have shown that both cell types fail to produce type I interferons (IFNs) in response to HIV-1 but that, unlike T cells, the virus does not block IFN induction by targeting IFN regulatory factor 3 (IRF3) for cellular degradation. Thus, either HIV-1 inhibits IFN induction by an alternate mechanism or, less likely, these cells fail to sense HIV-1. Here we show that HIV-1 (but not herpes simplex virus 2 [HSV-2] or Sendai virus)-exposed DCs and macrophages fail to induce the expression of all known type I and III IFN genes. These cells do sense the virus, and pattern recognition receptor (PRR)-induced signaling pathways are triggered. The precise stage in the IFN-inducing signaling pathway that HIV-1 targets to block IFN induction was identified; phosphorylation but not K63 polyubiquitination of TANK-binding kinase 1 (TBK1) was completely inhibited. Two HIV-1 accessory proteins, Vpr and Vif, were shown to bind to TBK1, and their individual deletion partly restored IFN-β expression. Thus, the inhibition of TBK1 autophosphorylation by binding of these proteins appears to be the principal mechanism by which HIV-1 blocks type I and III IFN induction in myeloid cells. IMPORTANCE Dendritic cells (DCs) and macrophages are key HIV target cells. Therefore, definition of how HIV impairs innate immune responses to initially establish infection is essential to design preventative interventions, especially by restoring initial interferon production. Here we demonstrate how HIV-1 blocks interferon induction by inhibiting the function of a key kinase in the interferon signaling pathway, TBK1, via two different viral accessory proteins. Other viral proteins have been shown to target the general effects of TBK1, but this precise targeting between ubiquitination and phosphorylation of TBK1 is novel.

The lineage relationships and fate of human dendritic cells (DCs) have significance for a number of diseases including HIV where both blood and tissue DCs may be infected. We used gene expression profiling of human monocyte and DC subpopulations sorted directly from blood and skin to define the lineage relationships. We also compared these with monocyte-derived DCs (MDDCs) and MUTZ3 Langerhans cells (LCs) to investigate their relevance as model skin DCs. Hierarchical clustering analysis showed that myeloid DCs clustered according to anatomical origin rather than putative lineage. Plasmacytoid DCs formed the most discrete cluster, but ex vivo myeloid cells formed separate clusters of cells both in blood and in skin. Separate and specific DC populations could be determined within skin, and the proportion of CD14⁺ dermal DCs (DDCs) was reduced and CD1a⁺ DDCs increased during culture, suggesting conversion to CD1a⁺-expressing cells in situ. This is consistent with origin of the CD1a⁺ DDCs from a local precursor rather than directly from circulating blood DCs or monocyte precursors. Consistent with their use as model skin DCs, the in vitro–derived MDDC and MUTZ3 LC populations grouped within the skin DC cluster. MDDCs clustered most closely to CD14⁺ DDCs; furthermore, common unique patterns of C-type lectin receptor expression were identified between these two cell types. MUTZ3 LCs, however, did not cluster closely with ex vivo–derived LCs. We identified differential expression of novel genes in monocyte and DC subsets including genes related to DC surface receptors (including C-type lectin receptors, TLRs, and galectins).