HIV turns plasmacytoid dendritic cells (pDC) into TRAIL-expressing killer pDC and down-regulates HIV coreceptors by Toll-like receptor 7-induced IFN-alpha

Abstract

Plasmacytoid dendritic cells (pDC) are key players in viral immunity and produce IFN-alpha after HIV-1 exposure, which in turn regulates TNF-related apoptosis-inducing ligand (TRAIL) expression by CD4(+) T cells. We show here that infectious and noninfectious HIV-1 virions induce activation of pDC into TRAIL-expressing IFN-producing killer pDC (IKpDC). IKpDC expressed high levels of activation markers (HLA-DR, CD80, CD83, and CD86) and the migration marker CCR7. Surprisingly, CXCR4 and CCR5 were down-regulated on IKpDC. We also show that HIV-1-induced IKpDC depended on Toll-like receptor 7 (TLR7) activation. HIV-1 or TLR7 agonistexposed IKpDC induced apoptosis of the CD4(+) T cell line SupT1 via the TRAIL pathway. Furthermore, IFN-alpha produced after HIV-induced TLR7 stimulation was responsible for TRAIL expression and the down-regulation of both CXCR4 and CCR5 by IKpDC. In contrast, activation and migration markers were not regulated by IFN-alpha. Finally, IFN-alpha increased the survival of IKpDC. We characterized a subset of pDC with a killer activity that is activated by endosomal-associated viral RNA and not by infection.

Fig. 1.

Characterization of pDC after treatment with AT-2 HIV-1. (A) Dot plot of BDCA4⁺ cells. pDC are defined as CD123⁺BDCA2⁺ cells. Shown is TRAIL expression on pDC cultured with microvesicles (pDC_mock, black) compared with AT-2 HIV-1 (pDC_HIV, red). (B) Increased CD83 expression on TRAIL⁺pDC_HIV (red) compared with pDC_Mock (black). (C) Increased CCR7 expression on TRAIL⁺pDC_HIV (red) compared with pDC_Mock (black). (D) Reduced expression of CCR5 on TRAIL⁺pDC_HIV (red) compared with pDC_Mock (black). Shown is reduced expression of CXCR4 on TRAIL⁺pDC_HIV (red) compared with pDC_Mock (black). (E) TRAIL expression on pDC_mock (black) or pDC_HIV (red) and pDC_HIV plus CQ (green). (F) TRAIL expression on pDC_mock (black) or pDC_HIV (red) and pDC_HIV plus A151 (green). (G) TRAIL expression on pDC_mock (black), pDC_HIV (red), and HIV_βCD (green).

Fig. 2.

Role of TLR7 in IKpDC activation. (A) Increase of TLR7 expression in pDC of HIV⁺ patients (n = 21) compared with HIV⁻ controls (n = 19) (MFI = 487 ± 58 and MFI = 99 ± 14, respectively; P = 0.001). (B) TRAIL expression on pDC_mock (Left) compared with Imiq-stimulated pDC (pDC_Imiq) (Right). (C) Expression of CD83 (Left) and CCR7 (Right) by TRAIL⁺pDC_Imiq (red) compared with pDC_mock (black). (D) Down-regulation of CCR5 (Left) and CXCR4 (Right) on TRAIL⁺pDC_Imiq (red) compared with pDC_mock (black). (E) IFN-α and TNF-α production and inhibition with A151. *, P < 0.05, two-tailed Student's t test.

Fig. 3.

TRAIL⁺pDC kill DR5⁺ T cell targets. pDC stimulated with microvesicles (pDC_Mock) or AT-2 HIV-1 (pDC_HIV) were used as effector cells against SupT1 target cells at various ratios in the absence or presence of a neutralizing anti-TRAIL antibody or matched isotype controls. Cytotoxicity was measured as the percentage of annexin V⁺ cells on the BDCA2⁻CD123⁻ cell population. Data are presented as the mean of three experiments ± 95% CI.

Fig. 4.

IFN-α regulation of TRAIL, CXCR4, and CCR5 by IKpDC. (A) TRAIL expression on pDC cultured overnight with AT-2 HIV-1 (Upper) or Imiq (Lower) in the absence (−Anti-IFN) or presence (+Anti-IFN) of antibodies against IFN-α. (B Left) Expression of CXCR4 on pDC_Mock (black), pDC_HIV (red), and pDC_HIV plus anti-IFN-α (green). (B Right) Expression of CCR5 on pDC_Mock (black), pDC_HIV (red), and pDC_HIV plus anti-IFN-α (green). (C) Down-regulation of CXCR4 (Left) and CCR5 (Right) by recombinant IFN-α. (D) Survival of isolated pDC in the presence of different stimuli during a 3-day period.