Attenuation of pathogenic immune responses during infection with human and simian immunodeficiency virus (HIV/SIV) by the tetracycline derivative minocycline.

HIV immune pathogenesis is postulated to involve two major mechanisms: 1) chronic innate immune responses that drive T cell activation and apoptosis and 2) induction of immune regulators that suppress T cell function and proliferation. Both arms are elevated chronically in lymphoid tissues of non-natural hosts, which ultimately develop AIDS. However, these mechanisms are not elevated chronically in natural hosts of SIV infection that avert immune pathogenesis despite similarly high viral loads. In this study we investigated whether minocycline could modulate these pathogenic antiviral responses in non-natural hosts of HIV and SIV. We found that minocycline attenuated in vitro induction of type I interferon (IFN) and the IFN-stimulated genes indoleamine 2,3-dioxygenase (IDO1) and TNF-related apoptosis inducing ligand (TRAIL) in human plasmacytoid dendritic cells and PBMCs exposed to aldrithiol-2 inactivated HIV or infectious influenza virus. Activation-induced TRAIL and expression of cytotoxic T-lymphocyte antigen 4 (CTLA-4) in isolated CD4+ T cells were also reduced by minocycline. Translation of these in vitro findings to in vivo effects, however, were mixed as minocycline significantly reduced markers of activation and activation-induced cell death (CD25, Fas, caspase-3) but did not affect expression of IFNß or the IFN-stimulated genes IDO1, FasL, or Mx in the spleens of chronically SIV-infected pigtailed macaques. TRAIL expression, reflecting the mixed effects of minocycline on activation and type I IFN stimuli, was reduced by half, but this change was not significant. These results show that minocycline administered after infection may protect against aspects of activation-induced cell death during HIV/SIV immune disease, but that in vitro effects of minocycline on type I IFN responses are not recapitulated in a rapid progressor model in vivo.

Transient increase of interferon-stimulated genes and no clinical benefit by chloroquine treatment during acute simian immunodeficiency virus infection of macaques.

Simian immunodeficiency virus (SIV) infection leads to AIDS in experimentally infected Rhesus macaques similarly to HIV-infected humans. In contrast, SIV infection of natural hosts is characterized by a down-regulation of innate acute responses to the virus within a few weeks of infection and results in limited pathology. Chloroquine (CQ) has been used in the treatment or prevention of malaria and has recently been shown to cause a decrease of immune activation and CD4 cell loss in HIV-infected individuals treated with antiretroviral therapy. Here, we treated Rhesus macaques with CQ during the acute phase of SIVmac251 infection with the intent to decrease viral-induced immune activation and possibly limit disease progression. Contrary to what was expected, CQ treatment resulted in a temporary increased expression of interferon (IFN)-stimulating genes and it worsened the recovery of CD4(+) T cells in the blood. Our findings confirm recent results observed in asymptomatic HIV-infected patients and suggest that CQ does not provide an obvious benefit in the absence of antiretroviral therapy.

Fatal pancreatitis in simian immunodeficiency virus SIV(mac251)-infected macaques treated with 2',3'-dideoxyinosine and stavudine following cytotoxic-T-lymphocyte-associated antigen 4 and indoleamine 2,3-dioxygenase blockade.

Human immunodeficiency virus (HIV) infection is associated with immune activation, CD4⁺-T-cell loss, and a progressive decline of immune functions. Antiretroviral therapy (ART) only partially reverses HIV-associated immune dysfunction, suggesting that approaches that target immune activation and improve virus-specific immune responses may be needed. We performed a preclinical study in rhesus macaques infected with the pathogenic simian immunodeficiency virus SIV(mac251) and treated with ART. We tested whether vaccination administered together with cytotoxic-T-lymphocyte-associated antigen 4 (CTLA-4) blockade and treatment with the indoleamine 2,3-dioxygenase (IDO) inhibitor 1-methyl-D-tryptophan (D-1mT), decreased immune activation and improved vaccine efficacy. The treatment did not augment vaccine immunogenicity; rather, it dramatically increased ART-related toxicity, causing all treated animals to succumb to acute pancreatitis and hyperglycemic coma. The onset of fulminant diabetes was associated with severe lymphocyte infiltration of the pancreas and complete loss of the islets of Langerhans. Thus, caution should be used when considering approaches aimed at targeting immune activation during ART.

Overactivation of plasmacytoid dendritic cells inhibits antiviral T-cell responses: a model for HIV immunopathogenesis.

A delicate balance between immunostimulatory and immunosuppressive signals mediated by dendritic cells (DCs) and other antigen-presenting cells (APCs) regulates the strength and efficacy of antiviral T-cell responses. HIV is a potent activator of plasmacytoid DCs (pDCs), and chronic pDC activation by HIV promotes the pathogenesis of AIDS. Cholesterol is pivotal in maintaining HIV envelope integrity and allowing HIV-cell interaction. By depleting envelope-associated cholesterol to different degrees, we generated virions with reduced ability to activate pDCs. We found that APC activation was dissociated from the induction of type I IFN-α/ß and indoleamine-2,3-dioxygenase (IDO)-mediated immunosuppression in vitro. Extensive cholesterol withdrawal, resulting in partial protein and RNA loss from the virions, rendered HIV a more powerful recall immunogen for stimulating memory CD8 T-cell responses in HIV-exposed, uninfected individuals. These enhanced responses were dependent on the inability of cholesterol-depleted HIV to induce IFN-α/ß.

Alloantigen-based AIDS vaccine: revisiting a "rightfully" discarded promising strategy.

This report revisits the accidental discovery that protection against simian immunodeficiency virus (SIV) infection in the early successful experimental AIDS vaccine studies in Rhesus macaques was due to antibodies directed against human leukocyte antigens (HLAs). The inactivated virus vaccine approach was discarded because protection was due to the host's immune reaction against the HLA acquired by SIV from the human cell lines in which it was grown, rather than against antigenic determinants of SIV itself. Subsequent studies have revealed that immune recognition of HLA on uninfected leukocytes also induces other factors that inhibit infection by both SIV and the human immunodeficiency virus. Pro and con aspects of immunization against HLA as a potential AIDS vaccine strategy are discussed.

Elevated systemic levels of inflammatory cytokines in older women with persistent cervical human papillomavirus infection.

BACKGROUND: Defects in lymphoproliferative responses to mitogens/antigens in women >45 years old with a persistent type-specific human papillomavirus (HPV) infection have been reported. METHODS: To determine whether these defects were associated with altered cytokine profiles, plasma and peripheral blood mononuclear cell (PBMC) culture supernatants from 50 cases (oversampled for their reduced lymphoproliferative ability) and 50 uninfected controls (oversampled for their robust lymphoproliferative ability) were examined for 24 cytokines using multiplexed bead-based immunoassays and ELISA. RESULTS: The following plasma cytokines were significantly increased in cases relative to controls (cases versus controls; median pg/mL): interleukin (IL)-6, 393.1 versus 14.5; IL-8, 1,128.5 versus 43.9; tumor necrosis factor-alpha (TNF-alpha), 164.1 versus 9.2; macrophage inflammatory protein-1alpha (MIP-1alpha), 1,368.9 versus 25.5; granulocyte macrophage colony-stimulating factor (GM-CSF), 13.8 versus 7.3; IL-1beta, 8.3 versus 1.6 (all P < 0.0001); and IL-1alpha, 218.2 versus 169.5 (P = 0.02). We focused our analysis on the cytokines IL-6, IL-8, TNF-alpha, and MIP-1alpha due to their high fold change (>10) and highly statistically significant difference between cases and controls. Length of persistence or type of infection (high risk and low risk) did not affect these differences. IL-6, TNF-alpha, and MIP-1alpha levels were also increased in unstimulated PBMC culture supernatants from cases compared with controls (P < 0.05), however, the cytokine levels from phytohemagglutinin-stimulated PBMC culture supernatants were significantly lower in the cases (P < 0.0001). CONCLUSIONS: Persistent HPV infection in older women with evidence of immune deficit is associated with an increase in systemic inflammatory cytokines. IMPACT: Future studies are needed to determine whether the inflammatory profile is age dependent and to examine the role that inflammatory cytokines play in HPV-induced progression from infection to cervical cancer.

TLR activation pathways in HIV-1-exposed seronegative individuals.

TLRs trigger innate immunity that recognizes conserved motifs of invading pathogens, resulting in cellular activation and release of inflammatory factors. The influence of TLR activation on resistance to HIV-1 infection has not been investigated in HIV-1 exposed seronegative (ESN) individuals. PBMCs isolated from heterosexually ESN individuals were stimulated with agonists specific for TLR3 (poly I:C), TLR4 (LPS), TLR7 (imiquimod), and TLR7/8 (ssRNA40). We evaluated expression of factors involved in TLR signaling cascades, production of downstream effector immune mediators, and TLR-expression in CD4+ and CD14+ cells. Results were compared with those obtained in healthy controls (HCs). ESN individuals showed: 1) comparable percentages of CD14+/TLR4+ and CD4+/TLR8+ CD14+/TLR8+ cells; 2) higher responsiveness to poly I:C, LPS, imiquimod, and ssRNA40 stimulation, associated with significantly increased production of IL-1beta, IL-6, TNF-alpha, and CCL3; 3) augmented expression of mRNA specific for other targets (CCL2, CSF3, CSF2, IL-1alpha, IL-8, IL-10, IL-12, cyclooxygenase 2) demonstrated by broader TLRs pathway expression analyses; and 4) increased MyD88/MyD88s(short) ratio, mainly following TLR7/8 stimulation. We also compared TLR-agonist-stimulated cytokine/chemokine production in CD14+ PBMCs and observed decreased IFN-beta production in ESN individuals compared with HCs upon TLR7/8-agonist stimulation. These data suggest that TLR stimulation in ESN individuals results in a more robust release of immunologic factors that can influence the induction of stronger adaptive antiviral immune responses and might represent a virus-exposure-induced innate immune protective phenotype against HIV-1.

Defective in vitro IL-2 production in lupus is an early but secondary event paralleling disease activity: evidence from the murine parent-into-F1 model supports staging of IL-2 defects in human lupus.

T cell defects are a well described feature of both human and murine lupus however their exact significance is unclear. Evidence from an induced model of lupus, the P --> F1 model of chronic lupus-like GVHD demonstrates that a secondary inducible T cell defect in in vitro IL-2 and CTL responses occurs early in the course of lupus-like disease and well in advance of clinical disease. Defective Th cell function was probed using a novel approach categorizing the response to two stimuli:1) the MHC self restricted response, termed self +X; and 2) the allogeneic response. Using this approach, lupus mice exhibited similar in vitro Th cell pattern i.e. an absent S+X response but preserved allogeneic (termed -/+). In contrast, human lupus patients exhibited three possible response patterns, +/+, - /+ or -/- with more severe in vitro T cell impairment correlated with more severe disease. Similarly, patients with other T cell mediated conditions i.e. HIV infection or renal allograft recipients, also exhibited more severe in vitro T cell impairment with greater disease activity or greater immunosuppression respectively. The similar Th response patterns in human and murine T cell mediated conditions indicates that the underlying mechanisms involved are not disease specific but instead reflect common immune responses and validate the use of the P --> F1 model for future studies of T cell mediated conditions. These results support the use of prospective monitoring of IL-2 responses in lupus patients. Successful adaptation of this approach to the clinical setting could allow not only earlier therapeutic intervention and reduced organ damage but also earlier tapering of pharmacological agents and reduced untoward effects.

Antiretroviral activity of the aminothiol WR1065 against Human Immunodeficiency virus (HIV-1) in vitro and Simian Immunodeficiency virus (SIV) ex vivo.

BACKGROUND: WR1065 is the free-thiol metabolite of the cytoprotective aminothiol amifostine, which is used clinically at very high doses to protect patients against toxicity induced by radiation and chemotherapy. In an earlier study we briefly reported that the aminothiol WR1065 also inhibits HIV-1 replication in phytohemagglutinin (PHA)-stimulated human T-cell blasts (TCBs) infected in culture for 2 hr before WR1065 exposure. In this study we expanded the original observations to define the dose-response curve for that inhibition, and address the question of additive effects for the combination of WR1065 plus Zidovudine (AZT). Here we also explored the effect of WR1065 on SIV by examining TCBs taken from macaques with well-established infections several months with SIV. RESULTS: TCBs from healthy human donors were infected for 2 hr with HIV-1, and viral replication (p24) was measured after 72 hr of incubation with or without WR1065, AZT, or both drugs. HIV-1 replication, in HIV-1-infected human TCBs, was inhibited by 50% at 13 microM WR1065, a dose at which 80% of the cells were viable. Cell cycle parameters were the same or equivalent at 0, 9.5 and 18.7 microM WR1065, showing no drug-related toxicity. Combination of AZT with WR1065 showed that AZT retained antiretroviral potency in the presence of WR1065. Cultured CD8+ T cell-depleted PHA-stimulated TCBs from Macaca mulatta monkeys chronically infected with SIV were incubated 17 days with WR1065, and viral replication (p27) and cell viability were determined. Complete inhibition (100%) of SIV replication (p27) was observed when TCBs from 3 monkeys were incubated for 17 days with 18.7 microM WR1065. A lower dose, 9.5 microM WR1065, completely inhibited SIV replication in 2 of the 3 monkeys, but cells from the third macaque, with the highest viral titer, only responded at the high WR1065 dose. CONCLUSION: The study demonstrates that WR1065 and the parent drug amifostine, the FDA-approved drug Ethyol, have antiretroviral activity. WR1065 was active against both an acute infection of HIV-1 and a chronic infection of SIV. The data suggest that the non-toxic drug amifostine may be a useful antiretroviral agent given either alone or in combination with other drugs as adjuvant therapy.

WR1065 mitigates AZT-ddI-induced mutagenesis and inhibits viral replication.

The success of nucleoside reverse transcriptase inhibitors (NRTIs) in treating HIV-1 infection and reducing mother-to-child transmission of the virus during pregnancy is accompanied by evidence that NRTIs cause long-term health risks for cancer and mitochondrial disease. Thus, agents that mitigate toxicities of the current combination drug therapies are needed. Previous work had shown that the NRTI-drug pair zidovudine (AZT)-didanosine (ddI) was highly cytotoxic and mutagenic; thus, we conducted preliminary studies to investigate the ability of the active moiety of amifostine, WR1065, to protect against the deleterious effects of this NRTI-drug pair. In TK6 cells exposed to 100 muM AZT-ddI (equimolar) for 3 days with or without 150 muM WR1065, WR1065 enhanced long-term cell survival and significantly reduced AZT-ddI-induced mutations. Follow-up studies were conducted to determine if coexposure to AZT and WR1065 abrogated the antiretroviral efficacy of AZT. In human T-cell blasts infected with HIV-1 in culture, inhibition of p24 protein production was observed in cells treated with 10 muM AZT in the absence or presence of 5-1,000 muM WR1065. Surprisingly, WR1065 alone exhibited dose-related inhibition of HIV-1 p24 protein production. WR1065 also had antiviral efficacy against three species of adenovirus and influenza A and B. Intracellular levels of unbound WR1065 were measured following in vitro/in vivo drug exposure. These pilot study results indicate that WR1065, at low intracellular levels, has cytoprotective and antimutagenic activities against the most mutagenic pair of NRTIs and has broad spectrum antiviral effects. These findings suggest that the activities have a possible common mode of action that merits further investigation.

Combined effect of antiretroviral therapy and blockade of IDO in SIV-infected rhesus macaques.

Increased activity of IDO, which catalyzes the degradation of Trp into kynurenine (Kyn), is observed during HIV/SIV infection, and it may contribute to the persistence of HIV/SIV by suppressing antiviral T cell responses. We administered the IDO inhibitor 1-methyl-d-tryptophan (d-1mT) for 13 days to SIV-infected rhesus macaques receiving antiretroviral therapy (ART). d-1mT treatment increased the plasma levels of Trp, without reducing the levels of Kyn, suggesting only a partial effect on IDO enzymatic activity. Surprisingly, d-1mT significantly reduced the virus levels in plasma and lymph nodes of ART-treated animals with incomplete responsiveness to ART. In SIV-infected animals that were not receiving ART, d-1mT was ineffective in reducing the plasma viral load and had only a marginal effect on the plasma Kyn/Trp ratio. Increased IDO and TGF-beta mRNA expression in lymph nodes of ART-treated macaques after d-1mT treatment suggested that compensatory counterregulatory mechanisms were activated by d-1mT, which may account for the lack of effect on plasma Kyn. Finally, d-1mT did not interfere with the ART-induced T cell dynamics in lymph nodes (increased frequency of total CD4 T cells, increase of CD8 T cells expressing the antiapoptotic molecule Bcl2, and reduction of regulatory T cells). Thus, d-1mT appeared to synergize with ART in inhibiting viral replication and did not interfere with the beneficial immunologic effects of ART. Further studies are required to elucidate the immunologic or virologic mechanism by which d-1mT inhibited SIV replication in vivo.

HAART reduces death ligand but not death receptors in lymphoid tissue of HIV-infected patients and simian immunodeficiency virus-infected macaques.

OBJECTIVE: To determine how antiretroviral therapy (ART) or HAART affects the expression of apoptotic ligands and their death receptors in the blood and lymphoid tissues of HIV-infected patients and simian immunodeficiency virus-infected macaques. METHODS: We analyzed the mRNA expression of death molecules [tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and FasL] and their receptors (DR5 and Fas) in blood and tonsils from HIV-infected patients (HIV positive), HIV-infected patients receiving HAART and HIV-uninfected (HIV negative) donors in a cross-sectional study. We comparatively analyzed mRNA expression of TRAIL and DR5 in blood and lymph nodes collected longitudinally from simian immunodeficiency virus-infected macaques before and after ART. RESULTS: Expression of TRAIL, FasL, DR5 and Fas was elevated in circulating CD4 T cells from a group of HIV-positive patients as compared with that from both HIV-negative donors and HAART patients. In a different study group, TRAIL, FasL, DR5 and Fas were increased in tonsils of HIV-positive patients as compared with HIV-negative donors and HAART patients. However, tonsils from HAART patients showed reduced expression of TRAIL and FasL but not DR5 and Fas as compared with HIV-positive patients. Similarly, data obtained in a longitudinal study of simian immunodeficiency virus-infected macaques showed that ART reduced both TRAIL and DR5 in peripheral blood but only TRAIL and not DR5 in lymph nodes from the same animals. CONCLUSION: These findings suggest that HAART or ART is ineffective in reducing the expression of apoptotic death receptors in lymphoid tissue. However, analysis limited to blood leukocytes may not reveal such a defect. Our results highlight the persistence of an underlying immunologic condition that may prevent therapy-induced restoration of CD4 T cells in lymphoid tissue.

HIV-induced type I interferon and tryptophan catabolism drive T cell dysfunction despite phenotypic activation.

Infection by the human immunodeficiency virus (HIV) is characterized by functional impairment and chronic activation of T lymphocytes, the causes of which are largely unexplained. We cultured peripheral blood mononuclear cells (PBMC) from HIV-uninfected donors in the presence or absence of HIV. HIV exposure increased expression of the activation markers CD69 and CD38 on CD4 and CD8 T cells. IFN-alpha/beta, produced by HIV-activated plasmacytoid dendritic cells (pDC), was necessary and sufficient for CD69 and CD38 upregulation, as the HIV-induced effect was inhibited by blockade of IFN-alpha/beta receptor and mimicked by recombinant IFN-alpha/beta. T cells from HIV-exposed PBMC showed reduced proliferation after T cell receptor stimulation, partially prevented by 1-methyl tryptophan, a competitive inhibitor of the immunesuppressive enzyme indoleamine (2,3)-dioxygenase (IDO), expressed by HIV-activated pDC. HIV-induced IDO inhibited CD4 T cell proliferation by cell cycle arrest in G1/S, and prevented CD8 T cell from entering the cell cycle by downmodulating the costimulatory receptor CD28. Finally, the expression of CHOP, a marker of the stress response activated by IDO, was upregulated by HIV in T cells in vitro and is increased in T cells from HIV-infected patients. Our data provide an in vitro model for HIV-induced T cell dysregulation and support the hypothesis that activation of pDC concomitantly contribute to phenotypic T cell activation and inhibition of T cell proliferative capacity during HIV infection.

PDL-1 upregulation on monocytes and T cells by HIV via type I interferon: restricted expression of type I interferon receptor by CCR5-expressing leukocytes.

The programmed death (PD)-1 interacts with its ligand (PDL-1) delivering a negative signal to T cells. During human immunodeficiency virus (HIV)-1 infection PD-1 and PDL-1 expressions are increased. Here we show that monocytes and CCR5(+) T cells of HIV-uninfected donors upregulated PDL-1 upon in vitro exposure to HIV. HIV-induced PDL-1 required interferon (IFN)-alpha, but not IFN-gamma, production. Inhibition of endocytosis, required for HIV-induced IFN-alpha production, prevented PDL-1 upregulation. IFN-alpha-inducing Toll-like receptor (TLR) agonists increased PDL-1 on monocytes and CCR5(+) T cells. CD80 and CD86 were also increased on monocytes and CCR5(+) T cells after HIV exposure, but only CD80 was IFN-alpha-dependent. IFN-alpha-receptor subunit 2 (IFNAR2), was expressed only by CCR5(+) T cells and monocytes, explaining why these leukocytes responded to HIV-induced IFN-alpha. Finally, T cell proliferation was improved by PDL-1 blockade in HIV-treated PBMC. In the setting of HIV infection, IFN-alpha may negatively affect T cell responses by inducing PDL-1.

Differential effect of type I and type II interferons on neopterin production and amino acid metabolism in human astrocyte-derived cells.

Intrathecal production of neopterin, a pteridine produced by interferon (IFN)-gamma-stimulated monocyte-derived macrophages, is associated with neurological disorders and infections. We investigated whether IFN-alpha/beta, IFN-gamma, or human immunodeficiency virus (HIV) induce neopterin production by human astroglioma cells. IFN-alpha/beta and IFN-gamma, but not HIV, induced neopterin. Interestingly, IFN-gamma, but not IFN-alpha/beta, increased expression and activity of the tryptophan-catabolizing enzyme indoleamine (2,3)-dioxygenase. In contrast, IFN-alpha/beta, but not IFN-gamma, reduced the uptake of three aromatic amino acids in U87MG and U138 astroglioma cells. Thus type I and type II IFN stimulate astrocyte-derived cells to produce neopterin and exert differential effects on amino acid metabolism.

Immune activation driven by CTLA-4 blockade augments viral replication at mucosal sites in simian immunodeficiency virus infection.

The importance of chronic immune activation in progression to AIDS has been inferred by correlative studies in HIV-infected individuals and in nonhuman primate models of SIV infection. Using the SIV(mac251) macaque model, we directly address the impact of immune activation by inhibiting CTLA-4, an immunoregulatory molecule expressed on activated T cells and a subset of regulatory T cells. We found that CTLA-4 blockade significantly increased T cell activation and viral replication in primary SIV(mac251) infection, particularly at mucosal sites, and increased IDO expression and activity. Accordingly, protracted treatment with anti-CTLA-4 Ab of macaques chronically infected with SIV(mac251) decreased responsiveness to antiretroviral therapy and abrogated the ability of therapeutic T cell vaccines to decrease viral set point. These data provide the first direct evidence that immune activation drives viral replication, and suggest caution in the use of therapeutic approaches for HIV infection in vivo that increase CD4(+) T cell proliferation.

Chronic innate immune activation as a cause of HIV-1 immunopathogenesis.

Human immunodeficiency virus (HIV)-1 infection causes progressive impairment of the immune system in humans, characterized by depletion of CD4 T cells and loss of T cell function. Increased markers of T cell activation and lymphoid hyperplasia suggest that chronic T cell activation persists in immunocompromised hosts, and contributes to the exhaustion of immune functions. Here we propose a revision of this hypothesis, in which we suggest that chronic activation of innate immunity may negatively affect adaptive T cell-mediated responses. We hypothesize that constant exposure of the effector cells of innate immunity to HIV results in their chronic hyperactivation, with deleterious effects on T cells. In particular, plasmacytoid dendritic cells (pDC) may be highly susceptible to HIV-induced activation due to its interaction with the cellular receptor CD4, expressed by pDC. Subsequent production of type I interferon and indoleamine 2,3-dioxygenase may exert suppressive and cytotoxic effects on T cells.

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

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.