HIV-1 Env and Nef Cooperatively Contribute to Plasmacytoid Dendritic Cell Activation via CD4-Dependent Mechanisms

Abstract

Plasmacytoid dendritic cells (pDCs) are the major source of type I IFN (IFN-I) in response to human immunodeficiency virus type 1 (HIV-1) infection. pDCs are rapidly activated during HIV-1 infection and are implicated in reducing the early viral load, as well as contributing to HIV-1-induced pathogenesis. However, most cell-free HIV-1 isolates are inefficient in activating human pDCs, and the mechanisms of HIV-1 recognition by pDCs and pDC activation are not clearly defined. In this study, we report that two genetically similar HIV-1 variants (R3A and R3B) isolated from a rapid progressor differentially activated pDCs to produce alpha interferon (IFN-␣). The highly pathogenic R3A efficiently activated pDCs to induce robust IFN-␣ production, while the less pathogenic R3B did not. The viral determinant for efficient pDC activation was mapped to the V1V2 region of R3A Env, which also correlated with enhanced CD4 binding activity. Furthermore, we showed that the Nef protein was also required for the activation of pDCs by R3A. Analysis of a panel of R3A Nef functional mutants demonstrated that Nef domains involved in CD4 downregulation were necessary for R3A to activate pDCs. Our data indicate that R3A-induced pDC activation depends on (i) the high affinity of R3A Env for binding the CD4 receptor and (ii) Nef activity, which is involved in CD4 downregulation. Our findings provide new insights into the mechanism by which HIV-1 induces IFN-␣ in pDCs, which contributes to pathogenesis. IMPORTANCE Plasmacytoid dendritic cells (pDCs) are the major type I interferon (IFN-I)-producing cells, and IFN-I actually contributes to pathogenesis during chronic viral infections. How HIV-1 activates pDCs and the roles of pDCs/IFN-I in HIV-1 pathogenesis remain unclear.We report here that the highly pathogenic HIV R3A efficiently activated pDCs to induce IFN-␣ production, while most HIV-1 isolates are inefficient in activating pDCs. We have discovered that R3A-induced pDC activation depends on (i) the high affinity of R3A Env for binding the CD4 receptor and (ii) Nef activity, which is involved in CD4 downregulation. Our findings thus provide new insights into the mechanism by which HIV-1 induces IFN-␣ in pDCs and contributes to HIV-1 pathogenesis. These novel findings will be of great interest to those working on the roles of IFN and pDCs in HIV-1 pathogenesis in general and on the interaction of HIV-1 with pDCs in particular. HIV-1 infection is characterized by both chronic immune activation and severe CD4 T cell loss, eventually progressing to AIDS. After more than 30 years of research, it is still unclear how HIV-1 infection leads to persistent immune activation and CD4 T cell depletion (1). Presumably, aberrant immune activation is a result of multiple factors that can contribute to the exhaustion and death of CD4 T cells in HIV-infected individuals. The mechanisms that are proposed to explain HIV-1-related chronic immune activation include disruption of intestinal integrity and microbial translocation (2); caspase-1-medi...

Numerous plasmacytoid dendritic cell infiltration in HIV‐associated psoriasis relieved only with antiretroviral therapy

“…7 In association with HIV, the pDC produce IFN-a under the stimulation of HIV components. 14 The case presented here showed high levels of pDC infiltration in the upper dermis of the HIV-associated psoriatic plaques, which were resolved with antiretroviral therapy alone. These findings suggest that the condition of HIV infection may activate pDC and recruit them to the dermis, leading the immunological cascade of psoriasis.…”

“…The pDC are, therefore, considered to potentially play a role in the onset of psoriasis because pDC infiltrate into the skin and produce IFN‐α early in the course of disease . In association with HIV, the pDC produce IFN‐α under the stimulation of HIV components . The case presented here showed high levels of pDC infiltration in the upper dermis of the HIV‐associated psoriatic plaques, which were resolved with antiretroviral therapy alone.…”

CD4 Receptor is a Key Determinant of Divergent HIV-1 Sensing by Plasmacytoid Dendritic Cells

“…While the spatiotemporal model of pDC sensing has been most clearly evaluated using synthetic TLR9 agonists (CpG), we have shown that the model also applies to HIV and TLR7, whereby HIV traffics to early endosomes in pDC, activating IRF7 signaling rather than NF-κB signaling [ 22 , 23 ]. The upstream events that determine activation of each of these pathways, and in particular, HIV virion trafficking in pDC, are currently unknown, however, prior studies suggest that HIV envelope may play a major role [ 13 , 30 , 31 ]. Here we demonstrate that HIV trafficking and pDC phenotype is predominantly determined by envelope-CD4 interaction, such that manipulation of HIV envelope or CD4 intracellular trafficking enables modulation of divergent sensing of HIV.…”

Glycosylphosphatidylinositol-Anchored Anti-HIV scFv Efficiently Protects CD4 T Cells from HIV-1 Infection and Deletion in hu-PBL Mice

“…Methods for the isolation of human PBMCs were described previously (55), and PBMCs were cryopreserved until use. CD4 T cells were negatively isolated from PBMCs by using an untouched Dynabeads human CD4 T cell kit (catalog number 11352D; Invitrogen) according to the manufacturer's instructions.…”