Type I interferon production in HIV-infected patients

Carrier-free micellar CpG interacting with cell membrane for enhanced immunological treatment of HIV-1

Unmethylated CpG motifs activate toll-like receptor 9 (TLR9), leading to sequence- and species-specific immune stimulation. Here, we engineered a CpG oligodeoxyribonucleotide (ODN) with multiple hydrophobic moieties, so-called lipid-modified uracil, which resulted in a facile micelle formation of the stimulant. The self-assembled CpG nanostructure (U4CpG) containing the ODN 2216 sequence was characterized by various spectroscopic and microscopic methods together with molecular dynamics simulations. Next, we evaluated the nano-immunostimulant for enhancement of anti-HIV immunity. U4CpG treatment induced activation of plasmacytoid dendritic cells (pDCs) and natural killer (NK) cells in healthy human peripheral blood, which produced type I interferons (IFNs) and IFN-γ in human peripheral blood mononuclear cells (PBMCs). Moreover, we validated the activation and promotion efficacy of U4CpG in patient-derived blood cells, and HIV-1 spread was significantly suppressed by a low dosage of the immunostimulant. Furthermore, U4CpG-treated PBMC cultured medium elicited transcription of latent HIV-1 in U1 cells indicating that U4CpG reversed HIV-1 latency. Thus, the functions of U4CpG in eradicating HIV-1 by enhancing immunity and reversing latency make the material a potential candidate for clinical studies dealing with viral infection.

Alprazolam Prompts HIV-1 Transcriptional Reactivation and Enhances CTL Response Through RUNX1 Inhibition and STAT5 Activation

The HIV-1 pandemic is a significant challenge to the field of medicine. Despite advancements in antiretroviral (ART) development, 38 million people worldwide still live with this disease without a cure. A significant barrier to the eradication of HIV-1 lies in the persistently latent pool that establishes early in the infection. The “shock and kill” strategy relies on the discovery of a latency-reversing agent (LRA) that can robustly reactivate the latent pool and not limit immune clearance. We have found that a benzodiazepine (BDZ), that is commonly prescribed for panic and anxiety disorder, to be an ideal candidate for latency reversal. The BDZ Alprazolam functions as an inhibitor of the transcription factor RUNX1, which negatively regulates HIV-1 transcription. In addition to the displacement of RUNX1 from the HIV-1 5′LTR, Alprazolam potentiates the activation of STAT5 and its recruitment to the viral promoter. The activation of STAT5 in cytotoxic T cells may enable immune activation which is independent of the IL-2 receptor. These findings have significance for the potential use of Alprazolam in a curative strategy and to addressing the neuroinflammation associated with neuroHIV-1.

Hyperbaric hyperoxia exposure in suppressing human immunodeficiency virus replication: An experimental in vitro in peripheral mononuclear blood cells culture

Cellular immune has an important role in response HIV infection, which is attack the infected cells to activate signaling molecule. Hyperbaric Oxygen (HBO) worked as complementary treatment for HIV infection. The production of ROS and RNS molecules during hyperbaric exposure can affect gene expression which contributes to cellular adaptative response. This study was conducted to explore the mechanisms of cellular adaptive response to HIV infection during hyperbaric exposure. This study was carried on in vitro using healthy volunteers’ PBMCs (Peripheral Blood Mononuclear Cells) cultures infected with HIV-1. The study was conducted as a posttest only group design. The experimental unit was PBMC from venous blood of healthy volunteers which were cultured in vitro and infected by co-culturing with HIV- 1 in MT4 cell line. The experimental unit consist of treatment and control group. Each group examined the expression of transcription factor NFκB, Interferon α, reverse transcriptase inhibitors (p21), and the amount of HIV-1 p24 antigen. There were increasingly significant differences in the expression of the trancription factor of NFκB, p21, andHIV-1 p24 antigen,as well as mRNA transcription of interferon α2 between treatment and controlgroup. By decreasing p24 antigen showed that HBO exposure was able to suppress HIV-1 replication. The exposure to hyperbaric oxygen at the pressure of 2.4 ATAand 98% oxygen wasable to produce ROS and RNS molecules, which play a role in cellular adaptive responses through increasing the expression of nfĸb, p21 and mRNA of interferon α2 plays a role in inhibition mechanism of HIV-1 replication in cells.

Sources of Type I Interferons in Infectious Immunity: Plasmacytoid Dendritic Cells Not Always in the Driver's Seat

Type I Interferons (IFNs) are hallmark cytokines produced in immune responses to all classes of pathogens. Type I IFNs can influence dendritic cell (DC) activation, maturation, migration, and survival, but also directly enhance natural killer (NK) and T/B cell activity, thus orchestrating various innate and adaptive immune effector functions. Therefore, type I IFNs have long been considered essential in the host defense against virus infections. More recently, it has become clear that depending on the type of virus and the course of infection, production of type I IFN can also lead to immunopathology or immunosuppression. Similarly, in bacterial infections type I IFN production is often associated with detrimental effects for the host. Although most cells in the body are thought to be able to produce type I IFN, plasmacytoid DCs (pDCs) have been termed the natural "IFN producing cells" due to their unique molecular adaptations to nucleic acid sensing and ability to produce high amounts of type I IFN. Findings from mouse reporter strains and depletion experiments in in vivo infection models have brought new insights and established that the role of pDCs in type I IFN production in vivo is less important than assumed. Production of type I IFN, especially the early synthesized IFNβ, is rather realized by a variety of cell types and cannot be mainly attributed to pDCs. Indeed, the cell populations responsible for type I IFN production vary with the type of pathogen, its tissue tropism, and the route of infection. In this review, we summarize recent findings from in vivo models on the cellular source of type I IFN in different infectious settings, ranging from virus, bacteria, and fungi to eukaryotic parasites. The implications from these findings for the development of new vaccination and therapeutic designs targeting the respectively defined cell types are discussed.

Deficit of IgG2 in HIV-positive pregnant women is responsible of inadequate IgG2 levels in their HIV-uninfected children in Malawi

BACKGROUND

Transplacental passage of IgGs is impaired in HIV + pregnant women, possibly determining an inadequate immunological protection in their children. We aimed to determine the impact of maternal immunological IgG profile and immunoactivation status on the efficiency of transplacental passage of IgG subclasses in HIV + mothers.

METHODS

16 mother/infants pairs were studied in Malawi. Mothers received antiretroviral therapy (ART) from the third trimester of pregnancy. Determinations of pre-ART levels of maternal sCD14, of IgG subclasses in mothers at delivery and in their 1-month-old infants, were performed using commercial ELISA kits.

RESULTS

At delivery, after a median of 10 weeks of ART, 12/16 mothers were hypergammaglobulinemic, with IgG levels (20.5 mg/ml, 95% CI:18.8-26.8) directly correlated to the plasmatic levels of sCD14 (r = 0.640, p = 0.014). IgG1 levels (17.9 mg/ml) accounted for 82% of IgG, IgG3 and IgG4 levels were in the normal range. A profound deficit of IgG2 was observed both in mothers (0.60 mg/ml) and in infants (0.14 mg/ml). Placental transfer ratio (range 0.16-0.42) did not show a selective impairment between the different IgG subclasses. The transplacental passage of all IgG subclasses was decreased in the presence of maternal IgG over 16 mg/ml (significantly for IgG1, p = 0.031) and of high levels of sCD14 (p = 0.063).

CONCLUSIONS

Transplacental passage was reduced for all IgG subclasses and inversely correlated to high levels of maternal IgGs and to the degree of immunoactivation. The profound depression of IgG2 in mothers suggests that IgG2 neonatal levels mostly reflect the maternal deficit rather than a selective impairment of IgG2 transfer.

Impairment of the type I interferon response by HIV-1: Potential targets for HIV eradication

By interfering with the type I interferon (IFN1) response, human immunodeficiency virus 1 (HIV-1) can circumvent host antiviral signalling and establish persistent viral reservoirs. HIV-1-mediated defects in the IFN pathway are numerous, and include the impairment of protein receptors involved in pathogen detection, downstream signalling cascades required for IFN1 upregulation, and expression or function of key IFN1-inducible, antiviral proteins. Despite this, the activation of IFN1-inducible, antiviral proteins has been shown to facilitate the killing of latently HIV-infected cells in vitro. Understanding how IFN1 signalling is blocked in physiologically-relevant models of HIV-1 infection, and whether these defects can be reversed, is therefore of great importance for the development of novel therapeutic strategies aimed at eradicating the HIV-1 reservoir.

ADAR1 and PACT contribute to efficient translation of transcripts containing HIV-1 trans-activating response (TAR) element

Human immunodeficiency virus type 1 (HIV-1) has evolved various measures to counter the host cell's innate antiviral response during the course of infection. Interferon (IFN)-stimulated gene products are produced following HIV-1 infection to limit viral replication, but viral proteins and RNAs counteract their effect. One such mechanism is specifically directed against the IFN-induced Protein Kinase PKR, which is centrally important to the cellular antiviral response. In the presence of viral RNAs, PKR is activated and phosphorylates the translation initiation factor eIF2α. This shuts down the synthesis of both host and viral proteins, allowing the cell to mount an effective antiviral response. PACT (protein activator of PKR) is a cellular protein activator of PKR, primarily functioning to activate PKR in response to cellular stress. Recent studies have indicated that during HIV-1 infection, PACT's normal cellular function is compromised and that PACT is unable to activate PKR. Using various reporter systems and in vitro kinase assays, we establish in this report that interactions between PACT, ADAR1 and HIV-1-encoded Tat protein diminish the activation of PKR in response to HIV-1 infection. Our results highlight an important pathway by which HIV-1 transcripts subvert the host cell's antiviral activities to enhance their translation.

Chronic Type I IFN Is Sufficient To Promote Immunosuppression through Accumulation of Myeloid-Derived Suppressor Cells

Failure of the immune system to eradicate viruses results in chronic viral infections, which are associated with increased susceptibility to secondary infections. Pathogenic HIV or lymphocytic choriomeningitis virus chronic infections display a persistent type I IFN signature. In chronic lymphocytic choriomeningitis virus infection, blockade of type I IFN signaling partially restores antiviral responses. In a mouse model, we tested whether chronic administration of type I IFN, at doses mimicking chronic viral infection, induced immunosuppression. Chronic exposure of mice to IFN-α alone was sufficient to strongly suppress specific CD8⁺ T cells responses to subsequent vaccinia virus infection. It resulted in the accumulation of Ly6C^hi monocytes. These monocytes were similar, phenotypically and functionally, to the myeloid-derived suppressor cells found in cancer because they exerted a potent suppression on CD8⁺ T cell responses in vitro. They acted at least partly through the l-arginine pathway. In vivo, their elimination restored antiviral CD8⁺ T cell responses. Our work provides a specific mechanism accounting for the role of IFN-α in immunosuppression and predicts that type I IFN modulation will be pivotal to cure human chronic infections, cancer, or autoimmune diseases.

Human Immunodeficiency Virus-1 Impairs IFN-Alpha Production Induced by TLR-7 Agonist in Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) play an important role in innate immune response against viruses, mainly through interferon-α (IFN-α) secretion. Impaired IFN-α secretion has been observed in patients with acute human immunodeficiency virus type 1 (HIV-1) infection and the reasons for this impairment are still obscure. To know the grounds behind this situation, HIV-1 viral copy numbers similar to those found in primary HIV-1 infection were used to stimulate peripheral blood mononuclear cells (PBMCs) and pDCs in this study. Intracellular IFN-α production was seen as early as 2 h in pDCs with TLR-7 agonist (imiquimod) stimulation, but HIV-1 required 48 h to induce secretion of IFN-α in supernatants and it was 10 times less compared to imiquimod. Thus, it shows that HIV-1 delays and impairs IFN-α production from pDCs. Furthermore, the IFN-α inhibitory activity of HIV-1 was checked by stimulating PBMCs and pDCs with imiquimod either simultaneously with HIV-1 or after 2 h pre-exposure to HIV-1. Pre-exposure to HIV-1 resulted in significant reduction in IFN-α secretion by pDCs and PBMCs when compared to imiquimod alone. In addition, simultaneous stimulation of these populations with HIV-1 and imiquimod resulted in significant impairment in IFN-α production in pDCs but not in PBMCs. HIV-1 not only fails to induce IFN-α in adequate quantities but also inhibits IFN-α secretary capacity of pDCs. HIV-1 particles were found to bind CD303 receptor on pDC surface probably blocking initiation of cascade leading to IFN-α impairment. The understanding of the pathways that lead to this suppression may help in devising the HIV control strategies.

Placental transfer of anti-group B Streptococcus immunoglobulin G antibody subclasses from HIV-infected and uninfected women to their uninfected infants

OBJECTIVES

Placental antibody transfer is impaired in the context of HIV infection, which may render HIV-exposed, uninfected infants vulnerable to group B Streptococcus (GBS) disease. The GBS antibody response predominately consists of immunoglobulin G2 (IgG2) antibody. Thus we determined whether concentration and placental transfer of anti-GBS antibody subclasses was altered in HIV-infected compared with HIV-uninfected mothers.

DESIGN

A retrospective analysis of anti-GBS antibody subclasses in 38 HIV-infected and 33 HIV-uninfected mothers and their uninfected infants.

METHODS

Sera were analysed using a novel flow cytometric assay that quantified binding of IgG1, IgG2, IgG3 and IgG4 to serotype (ST)Ia, STIII and STV GBS bacteria.

RESULTS

IgG2 binding to GBS STIa and V was lower in HIV-infected women compared with HIV-uninfected women. Moreover, IgG2 binding to GBS STIa was also lower in HIV-exposed, uninfected infants compared with unexposed infants. However, there were no statistically significant differences in the transplacental transfer ratio of IgG2 for any GBS serotype. The transplacental transfer of total IgG was reduced for GBS STIII and V and IgG1 subclass for STIII; placental transfer of all other subclasses was comparable in HIV-affected and HIV-unaffected pregnancies.

CONCLUSION

Anti-GBS IgG2 placental transfer is not affected by HIV infection. This is important for functional antibody against the capsular polysaccharide of GBS and provides confidence that maternal GBS vaccination may result in functional activity in HIV-infected and uninfected women.

Gut-Resident Lactobacillus Abundance Associates with IDO1 Inhibition and Th17 Dynamics in SIV-Infected Macaques

Gut microbes can profoundly modulate mucosal barrier-promoting Th17 cells in mammals. A salient feature of HIV/simian immunodeficiency virus (SIV) immunopathogenesis is the loss of Th17 cells, which has been linked to increased activity of the immunomodulatory enzyme, indoleamine 2,3-dioxygenase 1 (IDO 1). The role of gut microbes in this system remains unknown, and the SIV-infected rhesus macaque provides a well-described model for HIV-associated Th17 loss and mucosal immune disruption. We observed a specific depletion of gut-resident Lactobacillus during acute and chronic SIV infection of rhesus macaques, which was also seen in early HIV-infected humans. This depletion in rhesus macaques correlated with increased IDO1 activity and Th17 loss. Macaques supplemented with a Lactobacillus-containing probiotic exhibited decreased IDO1 activity during chronic SIV infection. We propose that Lactobacillus species inhibit mammalian IDO1 and thus may help to preserve Th17 cells during pathogenic SIV infection, providing support for Lactobacillus species as modulators of mucosal immune homeostasis.

Plasmacytoid dendritic cells promote HIV-1-induced group 3 innate lymphoid cell depletion

Group 3 innate lymphoid cells (ILC3s) have demonstrated roles in promoting antibacterial immunity, maintaining epithelial barrier function, and supporting tissue repair. ILC3 alterations are associated with chronic inflammation and inflammatory disease; however, the characteristics and relevant regulatory mechanisms of this cell population in HIV-1 infection are poorly understood due in part to a lack of a robust model. Here, we determined that functional human ILC3s develop in lymphoid organs of humanized mice and that persistent HIV-1 infection in this model depletes ILC3s, as observed in chronic HIV-1-infected patients. In HIV-1-infected mice, effective antiretroviral therapy reversed the loss of ILC3s. HIV-1-dependent reduction of ILC3s required plasmacytoid dendritic cells (pDCs), IFN-I, and the CD95/FasL pathway, as targeted depletion or blockade of these prevented HIV-1-induced ILC3 depletion in vivo and in vitro, respectively. Finally, we determined that HIV-1 infection induces CD95 expression on ILC3s via a pDC- and IFN-I-dependent mechanism that sensitizes ILC3s to undergo CD95/FasL-mediated apoptosis. We conclude that chronic HIV-1 infection depletes ILC3s through pDC activation, induction of IFN-I, and CD95-mediated apoptosis.

Interfering with immunity: detrimental role of type I IFNs during infection

Type I IFNs are known to inhibit viral replication and mediate protection against viral infection. However, recent studies revealed that these cytokines play a broader and more fundamental role in host responses to infections beyond their well-established antiviral function. Type I IFN induction, often associated with microbial evasion mechanisms unique to virulent microorganisms, is now shown to increase host susceptibility to a diverse range of pathogens, including some viruses. This article presents an overview of the role of type I IFNs in infections with bacterial, fungal, parasitic, and viral pathogens and discusses the key mechanisms mediating the regulatory function of type I IFNs in pathogen clearance and tissue inflammation.

HIV-1 translation and its regulation by cellular factors PKR and PACT

The synthesis of proteins from viral mRNA is the first step towards viral assembly. Viruses are dependent upon the cellular translation machinery to synthesize their own proteins. The synthesis of proteins from the human immunodeficiency virus (HIV) type 1 and 2 RNAs utilize several alternative mechanisms. The regulation of viral protein production requires a constant interplay between viral requirements and the cell response to viral infection. Among the antiviral cell responses, the interferon-induced RNA activated protein kinase, PKR, regulates the cellular and viral translation. During HIV-1 infection, PKR activation is highly regulated by viral and cellular factors. The cellular TAR RNA Binding Protein, TRBP, the Adenosine Deaminase acting on RNA, ADAR1, and the PKR Activator, PACT, play important roles. Recent data show that PACT changes its function from activator to inhibitor in HIV-1 infected cells. Therefore, HIV-1 has evolved to replicate in cells in which TRBP, ADAR1 and PACT prevent PKR activation to allow efficient viral protein synthesis. This proper translation will initiate the assembly of viral particles.

Innate immune responses and rapid control of inflammation in African green monkeys treated or not with interferon-alpha during primary SIVagm infection

Chronic immune activation (IA) is considered as the driving force of CD4⁺ T cell depletion and AIDS. Fundamental clues in the mechanisms that regulate IA could lie in natural hosts of SIV, such as African green monkeys (AGMs). Here we investigated the role of innate immune cells and IFN-α in the control of IA in AGMs. AGMs displayed significant NK cell activation upon SIVagm infection, which was correlated with the levels of IFN-α. Moreover, we detected cytotoxic NK cells in lymph nodes during the early acute phase of SIVagm infection. Both plasmacytoid and myeloid dendritic cell (pDC and mDC) homing receptors were increased, but the maturation of mDCs, in particular of CD16⁺ mDCs, was more important than that of pDCs. Monitoring of 15 cytokines showed that those, which are known to be increased early in HIV-1/SIVmac pathogenic infections, such as IL-15, IFN-α, MCP-1 and CXCL10/IP-10, were significantly increased in AGMs as well. In contrast, cytokines generally induced in the later stage of acute pathogenic infection, such as IL-6, IL-18 and TNF-α, were less or not increased, suggesting an early control of IA. We then treated AGMs daily with high doses of IFN-α from day 9 to 24 post-infection. No impact was observed on the activation or maturation profiles of mDCs, pDCs and NK cells. There was also no major difference in T cell activation or interferon-stimulated gene (ISG) expression profiles and no sign of disease progression. Thus, even after administration of high levels of IFN-α during acute infection, AGMs were still able to control IA, showing that IA control is independent of IFN-α levels. This suggests that the sustained ISG expression and IA in HIV/SIVmac infections involves non-IFN-α products.

Chronic inflammation is considered as directly involved in AIDS pathogenesis. The role of IFN-α as a driving force of chronic inflammation is under debate. Natural hosts of SIV, such as African green monkeys (AGMs), avoid chronic inflammation. We show for the first time that NK cells are strongly activated during acute SIVagm infection. This further demonstrates that AGMs mount a strong early innate immune response. Myeloid and plasmacytoid dendritic cells (mDCs and pDCs) homed to lymph nodes; however mDCs showed a stronger maturation profile than pDCs. Monitoring of cytokine profiles in plasma suggests that the control of inflammation in AGMs is starting earlier than previously considered, weeks before the end of the acute infection. We tested whether the capacity to control inflammation depends on the levels of IFN-α produced. When treated with high doses of IFN-α during acute SIVagm infection, AGMs did not show increase of immune activation or signs of disease progression. Our study provides evidence that the control of inflammation in SIVagm infection is not the consequence of weaker IFN-α levels. These data indicate that the sustained interferon-stimulated gene induction and chronic inflammation in HIV/SIVmac infections is driven by factors other than IFN-α.

Serial cervicovaginal exposures with replication-deficient SIVsm induce higher dendritic cell (pDC) and CD4+ T-cell infiltrates not associated with prevention but a more severe SIVmac251 infection of rhesus macaques

OBJECTIVE

Intravaginal exposure to simian immunodeficiency virus (SIV) acutely recruits interferon-alpha (IFN-α) producing plasmacytoid dendritic cells (pDC) and CD4 T-lymphocyte targets to the endocervix of nonhuman primates. We tested the impact of repeated cervicovaginal exposures to noninfectious, defective SIV particles over 72 hours on a subsequent cervicovaginal challenge with replication competent SIV.

METHODS

Thirty-four female Indian Rhesus macaques were given a 3-day twice-daily vaginal exposures to either SIVsmB7, a replication-deficient derivative of SIVsmH3 produced by a T lymphoblast CEMx174 cell clone (n = 16), or to CEM supernatant controls (n = 18). On the fourth day, animals were either euthanized to assess cervicovaginal immune cell infiltration or intravaginally challenged with SIVmac251. Challenged animals were tracked for plasma viral load and CD4 counts and euthanized at 42 days after infection.

RESULTS

At the time of challenge, macaques exposed to SIVsmB7, had higher levels of cervical CD123 pDCs (P = 0.032) and CD4 T cells (P = 0.036) than those exposed to CEM control. Vaginal tissues showed a significant increase in CD4 T-cell infiltrates (P = 0.048) and a trend toward increased CD68 cellular infiltrates. After challenge, 12 SIVsmB7-treated macaques showed 2.5-fold greater daily rate of CD4 decline (P = 0.0408), and viral load rise (P = 0.0036) as compared with 12 control animals.

CONCLUSIONS

Repeated nonproductive exposure to viral particles within a short daily time frame did not protect against infection despite pDC recruitment, resulting instead in an accelerated CD4 T-cell loss with an increased rate of viral replication.

Decoding the complexity of type I interferon to treat persistent viral infections

Type I interferons (IFN-I) are a broad family of cytokines that are central to the innate immune response. These proteins have long been appreciated for the critical roles they play in restraining viral infections and shaping antiviral immune responses. However, in recent years there has been increased awareness of the immunosuppressive actions of these proteins as well. Although there are many current therapeutic applications to manipulate IFN-I pathways, we have limited understanding of the mechanisms by which these therapies are actually functioning. In this review, we highlight the diversity and temporal impact of IFN-I signaling, discuss the current therapeutic uses of IFN-I, and explore the strategy of blocking IFN-I to alleviate immune dysfunction in persistent virus infections.

Type I interferon upregulates Bak and contributes to T cell loss during human immunodeficiency virus (HIV) infection

The role of Type I interferon (IFN) during pathogenic HIV and SIV infections remains unclear, with conflicting observations suggesting protective versus immunopathological effects. We therefore examined the effect of IFNα/β on T cell death and viremia in HIV infection. Ex vivo analysis of eight pro- and anti-apoptotic molecules in chronic HIV-1 infection revealed that pro-apoptotic Bak was increased in CD4+ T cells and correlated directly with sensitivity to CD95/Fas-mediated apoptosis and inversely with CD4+ T cell counts. Apoptosis sensitivity and Bak expression were primarily increased in effector memory T cells. Knockdown of Bak by RNA interference inhibited CD95/Fas-induced death of T cells from HIV-1-infected individuals. In HIV-1-infected patients, IFNα-stimulated gene expression correlated positively with ex vivo T cell Bak levels, CD95/Fas-mediated apoptosis and viremia and negatively with CD4+ T cell counts. In vitro IFNα/β stimulation enhanced Bak expression, CD95/Fas expression and CD95/Fas-mediated apoptosis in healthy donor T cells and induced death of HIV-specific CD8+ T cells from HIV-1-infected patients. HIV-1 in vitro sensitized T cells to CD95/Fas-induced apoptosis and this was Toll-like receptor (TLR)7/9- and Type I IFN-dependent. This sensitization by HIV-1 was due to an indirect effect on T cells, as it occurred in peripheral blood mononuclear cell cultures but not purified CD4+ T cells. Finally, peak IFNα levels and viral loads correlated negatively during acute SIV infection suggesting a potential antiviral effect, but positively during chronic SIV infection indicating that either the virus drives IFNα production or IFNα may facilitate loss of viral control. The above findings indicate stage-specific opposing effects of Type I IFNs during HIV-1 infection and suggest a novel mechanism by which these cytokines contribute to T cell depletion, dysregulation of cellular immunity and disease progression.

Insights from host genomics into HIV infection and disease: Identification of host targets for drug development

HIV susceptibility and disease progression show a substantial degree of individual heterogeneity, ranging from fast progressors to long-term non progressors or elite controllers, that is, subjects that control infection in the absence of therapy. Recent years have seen a significant increase in understanding of the host genetic determinants of susceptibility to HIV infection and disease progression, driven in large part by candidate gene studies, genome-wide association studies, genome-wide transcriptome analyses, and large-scale functional screens. These studies have identified common variants in host loci that clearly influence disease progression, characterized the scale and dynamics of gene and protein expression changes in response to infection, and provided the first comprehensive catalogue of genes and pathways involved in viral replication. This review highlights the potential of host genomic influences in antiviral therapy by pointing to promising novel drug targets but also providing the basis of the identification and validation of host mechanisms that might be susceptible targets for novel antiviral therapies.

The PKR activator, PACT, becomes a PKR inhibitor during HIV-1 replication

Background

HIV-1 translation is modulated by the activation of the interferon (IFN)-inducible Protein Kinase RNA-activated (PKR). PKR phosphorylates its downstream targets, including the alpha subunit of the eukaryotic translation Initiation Factor 2 (eIF2α), which decreases viral replication. The PKR Activator (PACT) is known to activate PKR after a cellular stress. In lymphocytic cell lines, HIV-1 activates PKR only transiently and not when cells replicate the virus at high levels. The regulation of this activation is due to a combination of viral and cellular factors that have been only partially identified.

Results

PKR is transiently induced and activated in peripheral blood mononuclear cells after HIV-1 infection. The addition of IFN reduces viral replication, and induces both the production and phosphorylation of PKR. In lymphocytic Jurkat cells infected by HIV-1, a multiprotein complex around PKR contains the double-stranded RNA binding proteins (dsRBPs), adenosine deaminase acting on RNA (ADAR)1 and PACT. In HEK 293T cells transfected with an HIV-1 molecular clone, PACT unexpectedly inhibited PKR and eIF2α phosphorylation and increased HIV-1 protein expression and virion production in the presence of either endogenous PKR alone or overexpressed PKR. The comparison between different dsRBPs showed that ADAR1, TAR RNA Binding Protein (TRBP) and PACT inhibit PKR and eIF2α phosphorylation in HIV-infected cells, whereas Staufen1 did not. Individual or a combination of short hairpin RNAs against PACT or ADAR1 decreased HIV-1 protein expression. In the astrocytic cell line U251MG, which weakly expresses TRBP, PACT mediated an increased HIV-1 protein expression and a decreased PKR phosphorylation. In these cells, a truncated PACT, which constitutively activates PKR in non-infected cells showed no activity on either PKR or HIV-1 protein expression. Finally, PACT and ADAR1 interact with each other in the absence of RNAs.

Conclusion

In contrast to its previously described activity, PACT contributes to PKR dephosphorylation during HIV-1 replication. This activity is in addition to its heterodimer formation with TRBP and could be due to its binding to ADAR1. HIV-1 has evolved to replicate in cells with high levels of TRBP, to induce the expression of ADAR1 and to change the function of PACT for PKR inhibition and increased replication.

Modulation of inflammasome-mediated pulmonary immune activation by type I IFNs protects bone marrow homeostasis during systemic responses to Pneumocystis lung infection

Although acquired bone marrow failure (BMF) is considered a T cell-mediated autoimmune disease, possible innate immune defects as a cause for systemic immune deviations in response to otherwise innocuous infections have not been extensively explored. In this regard, we recently demonstrated an important role of type I IFNs in protecting hematopoiesis during systemic stress responses to the opportunistic fungal pathogen Pneumocystis in lymphocyte-deficient mice. Mice deficient in both lymphocytes and type I IFN receptor (IFrag(-/-) mice) develop rapidly progressing BMF due to accelerated bone marrow (BM) cell apoptosis associated with innate immune deviations in the BM in response to Pneumocystis lung infection. However, the communication pathway between lung and BM eliciting the induction of BMF in response to this strictly pulmonary infection has been unclear. In this study, we report that absence of an intact type I IFN system during Pneumocystis lung infection not only causes BMF in lymphocyte-deficient mice but also transient BM stress in lymphocyte-competent mice. This is associated with an exuberant systemic IFN-γ response. IFN-γ neutralization prevented Pneumocystis lung infection-induced BM depression in type I IFN receptor-deficient mice and prolonged neutrophil survival time in BM from IFrag(-/-) mice. IL-1β and upstream regulators of IFN-γ, IL-12, and IL-18 were also upregulated in lung and serum of IFrag(-/-) mice. In conjunction, there was exuberant inflammasome-mediated caspase-1 activation in pulmonary innate immune cells required for processing of IL-18 and IL-1β. Thus, absence of type I IFN signaling during Pneumocystis lung infection may result in deregulation of inflammasome-mediated pulmonary immune activation, causing systemic immune deviations triggering BMF in this model.

KIR2DL4 copy number variation is associated with CD4+ T-cell depletion and function of cytokine-producing NK cell subsets in SIV-infected Mamu-A*01-negative rhesus macaques

Here, we demonstrate that KIR2DL4 copy number variation (CNV) is associated with CD4(+) T-cell decline and functionality of cytokine-producing NK cells during primary simian immunodeficiency virus (SIV) infection in Mamu-A*01(-) Indian-origin rhesus macaques, with higher KIR2DL4 copy numbers being associated with a better preservation of CD4(+) T cells and an increased gamma interferon (IFN-γ) production from stimulated cytokine-producing NK cell subsets during acute SIVmac251 infection. These findings underscore the crucial role of activating killer-cell immunoglobulin-like receptors (KIRs) in NK cell-mediated SIV responses during early SIV infection.

Interferon block to HIV-1 transduction in macrophages despite SAMHD1 degradation and high deoxynucleoside triphosphates supply

Background

Interferon-α (IFN-α) is an essential mediator of the antiviral response, which potently inhibits both early and late phases of HIV replication. The SAMHD1 deoxynucleoside triphosphate (dNTP) hydrolase represents the prototype of a new antiviral strategy we referred to as “nucleotide depletion”. SAMHD1 depletes dNTP levels in myeloid cells below those required for optimal synthesis of HIV viral DNA. HIV-2 and its SIVsm and SIVmac close relatives encode a protein termed Vpx, which counteracts SAMHD1. The potentiality of IFN-α to cooperate with nucleotide depletion has been poorly investigated so far. Here we wondered whether IFN-α affects SAMHD1 expression, Vpx-induced SAMHD1 degradation, Vpx-mediated rescue of HIV-1 transduction and the dNTP supply in monocyte-derived macrophages (MDMs).

Results

IFN-α inhibited HIV-1 transduction in monocytes and in MDMs while SAMHD1 expression was not up-regulated. Vpx triggered SAMHD1 degradation in IFN-α treated cells, and weakly restored HIV-1 transduction from the IFN-α block. Vpx helper effect towards HIV-1 transduction was gradually inhibited with increasing doses of IFN-α. dNTP levels were not significantly affected in MDMs and CD4+ primary activated T lymphocytes by IFN-α and, in correlation with SAMHD1 degradation, restoration of dNTP levels by Vpx was efficient in MDMs treated with the cytokine. In contrast, IFN-α inhibited Vpx-mediated SAMHD1 degradation in THP-1 cells, where, accordingly, Vpx could not rescue HIV-1 transduction.

Conclusion

Our results suggest that the early antiviral effect of IFN-α results from a mechanism independent of nucleotide depletion in MDMs. In addition, they indicate that the macrophage-like THP-1 cell line may provide a system to characterize an IFN-α-induced cell response that inhibits Vpx-mediated SAMHD1 degradation.

Concurrent measures of total and integrated HIV DNA monitor reservoirs and ongoing replication in eradication trials

OBJECTIVES

Interest in targeting HIV reservoirs is fueling trials that may decrease reservoir size and/or induce viral replication. Therefore, we aimed to develop strategies to sensitively measure changes in these parameters in patients on and off antiretroviral therapy (ART). Achieving these goals may help evaluate the effects of future clinical trials.

DESIGN

To determine the relationship between measurements of total and integrated HIV DNA and their role as markers of reservoir size and ongoing replication, these parameters were measured during the first year of ART, during long-term effective ART, and during a clinical trial aimed at targeting reservoirs.

METHODS

Total and integrated HIV DNA were measured in patient samples using quantitative PCR techniques. CD4(+)T cell counts and plasma viremia were also monitored.

RESULTS

Unintegrated HIV DNA became undetectable during the first year of ART. Total and integrated HIV DNA levels were generally equal in well controlled patients on ART, and low-level plasma viremia correlated best with integration measures. Finally, patients who controlled plasma viremia (<400 copies/ml) during interferon-α monotherapy exhibited a decrease in the level of integrated but not total HIV DNA and a rise in the ratio of total to integrated HIV DNA over time.

CONCLUSION

Our findings suggest that appearance of unintegrated HIV DNA reflects residual HIV expression and de-novo reverse transcription, providing insight into the mechanism by which interferon-α reduces the HIV reservoir. We conclude that concurrent measurements of total and integrated HIV DNA provide information regarding reservoir size and ongoing replication in trials targeting HIV.

Biology of plasmacytoid dendritic cells and natural killer cells in HIV-1 infection

PURPOSE

This review summarizes recent literature on the biology of dendritic cells and natural killer cells in HIV-1 infection and the importance of crosstalk between them in the development of strong antiviral immunity.

RECENT FINDINGS

Type I interferons produced by dendritic cells in response to HIV-1 have been suggested to act as a double-edged sword, stemming HIV-1 replication on the one hand and causing T-cell loss on the other. Recent epidemiologic evidence demonstrates a strong association between the natural killer cell receptor KIR3DS1 (along with its presumed ligand HLA-B Bw4-80I) in the control of HIV-1 replication.

SUMMARY

Dendritic and natural killer cells play a central role in the innate immune response to viral infections through both the direct elimination of infected cells and modulation of each other's function.

Interferon-alpha subtype 11 activates NK cells and enables control of retroviral infection

The innate immune response mediated by cells such as natural killer (NK) cells is critical for the rapid containment of virus replication and spread during acute infection. Here, we show that subtype 11 of the type I interferon (IFN) family greatly potentiates the antiviral activity of NK cells during retroviral infection. Treatment of mice with IFN-α11 during Friend retrovirus infection (FV) significantly reduced viral loads and resulted in long-term protection from virus-induced leukemia. The effect of IFN-α11 on NK cells was direct and signaled through the type I IFN receptor. Furthermore, IFN-α11-mediated activation of NK cells enabled cytolytic killing of FV-infected target cells via the exocytosis pathway. Depletion and adoptive transfer experiments illustrated that NK cells played a major role in successful IFN-α11 therapy. Additional experiments with Mouse Cytomegalovirus infections demonstrated that the therapeutic effect of IFN-α11 is not restricted to retroviruses. The type I IFN subtypes 2 and 5, which bind the same receptor as IFN-α11, did not elicit similar antiviral effects. These results demonstrate a unique and subtype-specific activation of NK cells by IFN-α11.

The innate immune response mediated by cells such as natural killer (NK) cells can contribute to immunity against viral infections. NK cells can kill virus-infected cells and thus inhibit virus replication and spread during acute infection. However, in infections with retroviruses, like HIV, these cells are not sufficient to prevent pathology. Here, we describe a new strategy to augment natural killer cell responses during virus infections by using a subtype of the type I interferon family as antiviral drug. This therapy strongly activated NK cells and enabled them to control retrovirus as well as herpes virus infections in mice. The new approach might have great potential for the treatment of many infectious and tumor diseases in which natural killer cells play a significant role in immunity.

Evaluation of different antiretroviral drug protocols on naturally infected feline immunodeficiency virus (FIV) cats in the late phase of the asymptomatic stage of infection

The aim of this study was to evaluate the efficacy of the antiretrovirals: Zidovudine (ZDV) alone; ZDV + Recombinant Human Interferon-α (rHuIFN-α); ZDV + Lamivudine (3TC) and ZDV + valproic acid (Valp) on naturally feline immunodeficiency virus (FIV)-infected cats, in the late phase of the asymptomatic stage of infection. The follow-up was performed over one year, through clinical evaluation and the determination of viral loads and CD4+/CD8+ ratios. Neurological signs were studied by visual and auditory evoked potentials (VEP, AEP) and the responses were abnormal in 80% of the FIV-infected cats. After one year, an improvement in VEP and AEP was observed in the ZDV + Valp group and a worsening in the group receiving ZDV + rHuIFN-α. The CD4+/CD8+ ratio showed a significant increase (both intra and inter-groups) only in ZDV and ZDV + 3TC, between their pre-treatment and one year values, as well as among the other groups. Viral load only showed a significant decrease in ZDV and ZDV + 3TC groups, when comparing the values at one year of treatment vs. pre-treatment values and when the different groups were compared. In addition, the viral load decrease was significantly more pronounced in the ZDV + 3TC vs. ZDV group. We conclude that ZDV and ZDV + 3TC produce significant reductions in viral load and stimulate a recovery of the CD4+/CD8+ ratio, compared with the other protocols. It is clear that the addition of 3TC resulted in a greater reduction in viral load than use of ZDV as a single drug. Therefore, the combination ZDV + 3TC could be more effective than the sole use of ZDV.

Type 1 interferons suppress accelerated osteoclastogenesis and prevent loss of bone mass during systemic inflammatory responses to Pneumocystis lung infection

HIV infection causes loss of CD4(+) T cells and type 1 interferon (IFN)-producing and IFN-responsive dendritic cells, resulting in immunodeficiencies and susceptibility to opportunistic infections, such as Pneumocystis. Osteoporosis and bone marrow failure are additional unexplained complications in HIV-positive patients and patients with AIDS, respectively. We recently demonstrated that mice that lack lymphocytes and IFN a/b receptor (IFrag(-/-)) develop bone marrow failure after Pneumocystis lung infection, whereas lymphocyte-deficient, IFN α/β receptor-competent mice (RAG(-/-)) had normal hematopoiesis. Interestingly, infected IFrag(-/-) mice also exhibited bone fragility, suggesting loss of bone mass. We quantified bone changes and evaluated the potential connection between progressing bone fragility and bone marrow failure after Pneumocystis lung infection in IFrag(-/-) mice. We found that Pneumocystis infection accelerated osteoclastogenesis as bone marrow failure progressed. This finding was consistent with induction of osteoclastogenic factors, including receptor-activated nuclear factor-κB ligand and the proapoptotic factor tumor necrosis factor-related apoptosis-inducing ligand, in conjunction with their shared decoy receptor osteoprotegerin, in the bone marrow of infected IFrag(-/-) mice. Deregulation of this axis has also been observed in HIV-positive individuals. Biphosphonate treatment of IFrag(-/-) mice prevented bone loss and protected loss of hematopoietic precursor cells that maintained activity in vitro but did not prevent loss of mature neutrophils. Together, these data show that bone loss and bone marrow failure are partially linked, which suggests that the deregulation of the receptor-activated nuclear factor-κB ligand/osteoprotegerin/tumor necrosis factor-related apoptosis-inducing ligand axis may connect the two phenotypes in our model.

Alpha interferon and HIV infection cause activation of human T cells in NSG-BLT mice

The development of small animal models for the study of HIV transmission is important for evaluation of HIV prophylaxis and disease pathogenesis. In humanized bone marrow-liver-thymus (BLT) mice, hematopoiesis is reconstituted by implantation of human fetal liver and thymus tissue (Thy/Liv) plus intravenous injection of autologous liver-derived hematopoietic stem progenitor cells (HSPC). This results in reconstitution of human leukocytes in the mouse peripheral blood, lymphoid organs, and mucosal sites. NOD-scid interleukin-2 receptor-negative (IL-2Rγ(-/-)) (NSG)-BLT mice were inoculated intravaginally with HIV and were monitored for plasma viremia by a branched DNA assay 4 weeks later. T-cell activation was determined by expression of CD38 and HLA-DR on human CD4(+) and CD8(+) T cells in mouse peripheral blood at the time of inoculation and 4 weeks later. Additional BLT mice were treated with human alpha interferon 2b (IFN-α2b) (intron A) and assessed for T-cell activation. Productive HIV infection in BLT mice was associated with T-cell activation (increases in CD38 mean fluorescence intensity and both the frequency and absolute number of CD38(+) HLA-DR(+) T cells) that correlated strongly with plasma viral load and was most pronounced in the CD8(+) T-cell compartment. This T-cell activation phenotype was recapitulated in NSG-BLT mice treated with intron A. HIV susceptibility correlated with the number of HSPC injected, yet a number of mice receiving the Thy/Liv implant alone, with no HSPC injection, were also susceptible to intravaginal HIV. These results are consistent with studies linking T-cell activation to progressive disease in humans and lend support for the use of NSG-BLT mice in studies of HIV pathogenesis.

The human transcriptome during nontyphoid Salmonella and HIV coinfection reveals attenuated NFkappaB-mediated inflammation and persistent cell cycle disruption

Background. Invasive nontyphoid Salmonella (iNTS) disease is common and severe in adults with human immunodeficiency virus (HIV) infection in Africa. We previously observed that ex vivo macrophages from HIV-infected subjects challenged with Salmonella Typhimurium exhibit dysregulated proinflammatory cytokine responses.

Methods. We studied the transcriptional response in whole blood from HIV-positive patients during acute and convalescent iNTS disease compared to other invasive bacterial diseases, and to HIV-positive and -negative controls.

Results. During iNTS disease, there was a remarkable lack of a coordinated inflammatory or innate immune signaling response. Few interferon γ (IFNγ)--induced genes or Toll-like receptor/transcription factor nuclear factor κB (TLR/NFκB) gene pathways were upregulated in expression. Ex vivo lipopolysacharide (LPS) or flagellin stimulation of whole blood, however, showed that convalescent iNTS subjects and controls were competent to mount prominent TLR/NFκB-associated patterns of mRNA expression. In contrast, HIV-positive patients with other invasive bacterial infections (Escherichia coli and Streptococcus pneumoniae) displayed a pronounced proinflammatory innate immune transcriptional response. There was also upregulated mRNA expression in cell cycle, DNA replication, translation and repair, and viral replication pathways during iNTS. These patterns persisted for up to 2 months into convalescence.

Conclusions. Attenuation of NFκB-mediated inflammation and dysregulation of cell cycle and DNA-function gene pathway expression are key features of the interplay between iNTS and HIV.

The gp41 epitope, QARVLAVERY, is highly conserved and a potent inducer of IgA that neutralizes HIV-1 and inhibits viral transcytosis

Mucosal surfaces are the predominant site of human immunodeficiency virus (HIV)-1 transmission. For prophylactic approaches to effectively prevent HIV infection and subsequent dissemination, the induction of mucosally relevant protective immunity will be critical. Here, we have characterized the antibody (Ab) response generated by a highly conserved gp41epitope, QARVLAVERY, in an optimized immunization model that elicits potent epitope-specific Abs in the serum, vaginal washes, and fecal secretions of immunized mice. Our results show that QARVLAVERY is indeed a potent inducer of IgA and importantly, QARVLAVERY-specific IgA was effective in neutralizing HIV and inhibiting viral transcytosis. Intriguingly, QARVLAVERY also generated an approximate 1:1 ratio of IgG:IgA in the serum of immunized mice, independent of the delivery regimen and produced early systemic IgA, even before IgG. In light of the significantly high IgA induction by QARVLAVERY and the functionality of epitope-specific Abs in the inhibition of HIV infection and transcytosis, QARVLAVERY is an attractive epitope to be considered in mucosal vaccination strategies against HIV.

Innate sensing of HIV-infected cells

Cell-free HIV-1 virions are poor stimulators of type I interferon (IFN) production. We examined here how HIV-infected cells are recognized by plasmacytoid dendritic cells (pDCs) and by other cells. We show that infected lymphocytes are more potent inducers of IFN than virions. There are target cell-type differences in the recognition of infected lymphocytes. In primary pDCs and pDC-like cells, recognition occurs in large part through TLR7, as demonstrated by the use of inhibitors and by TLR7 silencing. Donor cells expressing replication-defective viruses, carrying mutated reverse transcriptase, integrase or nucleocapsid proteins induced IFN production by target cells as potently as wild-type virus. In contrast, Env-deleted or fusion defective HIV-1 mutants were less efficient, suggesting that in addition to TLR7, cytoplasmic cellular sensors may also mediate sensing of infected cells. Furthermore, in a model of TLR7-negative cells, we demonstrate that the IRF3 pathway, through a process requiring access of incoming viral material to the cytoplasm, allows sensing of HIV-infected lymphocytes. Therefore, detection of HIV-infected lymphocytes occurs through both endosomal and cytoplasmic pathways. Characterization of the mechanisms of innate recognition of HIV-infected cells allows a better understanding of the pathogenic and exacerbated immunologic events associated with HIV infection.

AIDS is characterized by a hyperactivation of the immune system. Innate and inflammatory responses, associated with an exacerbated production of cytokines like type I interferons (IFN) and of chemokines, deregulate the normal functioning of T lymphocytes and other cells. The events that trigger this inappropriate activation remain poorly understood. Plasmacytoid dendritic cells (pDCs) normally produce IFN when they encounter viruses. Here we examined how HIV-infected cells are recognized by pDCs, as well as by other immune and non-immune cells. We show that viruses transmitted via cell-to-cell contacts are more potent inducers of IFN than cell-free viral particles. In pDCs, recognition occurs in large part through TLR7, a cellular receptor detecting viral genetic materials after capture in intracellular vesicles. Donor cells expressing replication-defective viruses are also able to trigger IFN production by target cells. We further show that in TLR7-negative, non-hematopoietic cells an additional cytoplasmic pathway allows sensing of HIV-infected lymphocytes. Therefore, detection of HIV-infected lymphocytes occurs at different intracellular localizations, and does not require ongoing viral replication. Characterization of the mechanisms of innate HIV-1 recognition allows a better understanding of the pathology of HIV infection, and has consequences for the design of vaccine strategies.

Multiple levels of PKR inhibition during HIV-1 replication

Recent therapeutic approaches against HIV-1 include IFN in combination therapy for patients with coinfections or as an alternative strategy against the virus. These treatment options require a better understanding of the weak efficacy of the IFN-stimulated genes, such as the protein kinase RNA-activated (PKR), which results in viral progression. Activated PKR has a strong antiviral activity on HIV-1 expression and production in cell culture. However, PKR is not activated upon HIV-1 infection when the virus reaches high levels of replication, due to viral and cellular controls. PKR is activated by low levels of the HIV-1 trans-activation response (TAR) RNA element, but is inhibited by high levels of this double-stranded RNA. The viral Tat protein also counteracts PKR activation by several mechanisms. In addition, HIV-1 replicates only in cells that have a high level of the TAR RNA binding protein (TRBP), a strong inhibitor of PKR activation. Furthermore, increased levels of adenosine deaminase acting on RNA (ADAR1) are observed when HIV-1 replicates at high levels and the protein binds to PKR and inhibits its activation. Finally, the PKR activator (PACT) also binds to PKR during HIV-1 replication with no subsequent kinase activation. The combination of all the inhibiting pathways that prevent PKR phosphorylation contributes to a high HIV-1 production in permissive cells. Enhancing PKR activation by counteracting its inhibitory partners could establish an increased innate immune antiviral pathway against HIV-1 and could enhance the efficacy of the IFN treatment.

Immune mechanisms of HIV control

HIV-1 can be contained by the immune system, as demonstrated by the existence of rare individuals who spontaneously control HIV-1 replication in the absence of antiretroviral therapy. Emerging evidence points to the importance of a very active cellular immune response in mediating HIV-1 control. The rapid induction of interferon-dependent HIV restriction factors, the presence of protective MHC class I alleles, and the development of a high avidity T-cell response may all cooperate in limiting HIV replication at an early stage. This review will focus on recent advances in understanding the immune mechanisms of HIV control, and on the lessons that may be drawn for the development of candidate HIV vaccines.

HIV-1 matrix protein p17: a candidate antigen for therapeutic vaccines against AIDS

The success in the development of anti-retroviral therapies (HAART) that contain human immunodeficiency virus type 1 (HIV-1) infection is challenged by the cost of this lifelong therapy and by its toxicity. Immune-based therapeutic strategies that boost the immune response against HIV-1 proteins or protein subunits have been recently proposed to control virus replication in order to provide protection from disease development, reduce virus transmission, and help limit the use of anti-retroviral treatments. HIV-1 matrix protein p17 is a structural protein that is critically involved in most stages of the life cycle of the retrovirus. Besides its well established role in the virus life cycle, increasing evidence suggests that p17 may also be active extracellularly in deregulating biological activities of many different immune cells that are directly or indirectly involved in AIDS pathogenesis. Thus, p17 might represent a promising target for developing a therapeutic vaccine as a contribution to combating AIDS. In this article we review the biological characteristics of HIV-1 matrix protein p17 and we describe why a synthetic peptide representative of the p17 functional epitope may work as a vaccine molecule capable of inducing anti-p17 neutralizing response against p17 derived from divergent HIV-1 strains.

Suppression of human immunodeficiency virus type 1 replication in macrophages by commensal bacteria preferentially stimulating Toll-like receptor 4

Protection from primary human immunodeficiency virus type 1 (HIV-1) infection has not yet been accomplished by vaccines inducing HIV-1-specific acquired immunity. Nevertheless, it has been reported that a small subgroup of women remain resistant to HIV-1 infection under natural conditions. If similar conditions can be induced in uninfected individuals, it will contribute the first line of protection against HIV-1 infection, and also improve the effects of anti-HIV-1 vaccines. We reasoned that innate immunity may be involved in the resistance to HIV-1 infection, and investigated the effects of various Toll-like receptor (TLR) ligands and commensal bacteria on HIV-1 replication in macrophages, one of the initial targets of HIV-1 infection and also the main mediators of innate immunity. We established the HIV-1 reporter monocytic cell line, THP-1/NL4-3luc, which could be differentiated into macrophage-like cells in vitro. In these cells, stimulation of TLR3 and TLR4 by their ligands suppressed HIV-1 expression partly through type I interferon (IFN). Among the commensal bacteria tested, Escherichia coli, Veillonella parvula and Neisseria mucosa suppressed HIV-1 expression, whereas Lactobacillus acidophilus, Prevotella melaninogenica, P. bivia and Mycobacterium smegmatis enhanced it. The bacteria with suppressive effects preferentially stimulated TLR4, whereas the ones with enhancing effects stimulated TLR2. Neutralizing antibodies against TLR4 and IFN-α/β receptor abrogated bacterially mediated HIV-1 suppression. Suppressive effects of E. coli, V. parvula and N. mucosa on HIV-1 replication were reproducible in primary monocyte-derived macrophages following acute HIV-1 infection. These findings suggest that certain commensal bacteria preferentially stimulating TLR4 potentially produce local environments resistant to HIV-1 infection.

Nonpathogenic SIV infection of African green monkeys induces a strong but rapidly controlled type I IFN response

African green monkeys (AGMs) infected with the AGM type of SIV (SIVagm) do not develop chronic immune activation and AIDS, despite viral loads similar to those detected in humans infected with HIV-1 and rhesus macaques (RMs) infected with the RM type of SIV (SIVmac). Because chronic immune activation drives progressive CD4+ T cell depletion and immune cell dysfunctions, factors that characterize disease progression, we sought to understand the molecular basis of this AGM phenotype. To this end, we longitudinally assessed the gene expression profiles of blood- and lymph node-derived CD4+ cells from AGMs and RMs in response to SIVagm and SIVmac infection, respectively, using a genomic microarray platform. The molecular signature of acute infection was characterized, in both species, by strong upregulation of type I IFN-stimulated genes (ISGs). ISG expression returned to basal levels after postinfection day 28 in AGMs but was sustained in RMs, especially in the lymph node-derived cells. We also found that SIVagm induced IFN-alpha production by AGM cells in vitro and that low IFN-alpha levels were sufficient to induce strong ISG responses. In conclusion, SIV infection triggered a rapid and strong IFN-alpha response in vivo in both AGMs and RMs, with this response being efficiently controlled only in AGMs, possibly as a result of active regulatory mechanisms.

Inability of plasmacytoid dendritic cells to directly lyse HIV-infected autologous CD4+ T cells despite induction of tumor necrosis factor-related apoptosis-inducing ligand

The function of plasmacytoid dendritic cells (PDC) in chronic human immunodeficiency virus type 1 (HIV-1) infection remains controversial with regard to its potential for sustained alpha interferon (IFN-alpha) production and induction of PDC-dependent tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated cytotoxicity of HIV-infected cells. We address these areas by a study of chronically HIV-1-infected subjects followed through antiretroviral therapy (ART) interruption and by testing PDC cytolytic function against autologous HIV-infected CD4(+) T cells. Rebound in viremia induced by therapy interruption showed a positive association between TRAIL and viral load or T-cell activation, but comparable levels of plasma IFN-alpha/beta were found in viremic ART-treated and control subjects. While PDC from HIV-infected subjects expressed less interferon regulator factor 7 (IRF-7) and produced significantly less IFN-alpha upon Toll-like receptor 7/9 (TLR7/9) engagement than controls, membrane TRAIL expression in PDC from HIV(+) subjects was increased. Moreover, no significant increase in death receptor 5 (DR5) expression was seen in CD4(+) T cells from viremic HIV(+) subjects compared to controls or following in vitro infection/exposure to infectious and noninfectious virus or exogenous IFN-alpha, respectively. Although activated PDC killed the DR5-expressing HIV-infected Sup-T1 cell line, PDC did not lyse primary autologous HIV(+) CD4(+) T cells yet could provide accessory help for NK cells in killing HIV-infected autologous CD4(+) T cells. Taken together, our data show a lack of sustained high levels of soluble IFN-alpha in chronic HIV-1 infection in vivo and document a lack of direct PDC cytolytic activity against autologous infected or uninfected CD4(+) T cells.

Plasmacytoid dendritic cells and the control of herpesvirus infections

Type-I interferons (IFN-I) are cytokines essential for vertebrate antiviral defense, including against herpesviruses. IFN-I have potent direct antiviral activities and also mediate a multiplicity of immunoregulatory functions, which can either promote or dampen antiviral adaptive immune responses. Plasmacytoid dendritic cells (pDCs) are the professional producers of IFN-I in response to many viruses, including all of the herpesviruses tested. There is strong evidence that pDCs could play a major role in the initial orchestration of both innate and adaptive antiviral immune responses. Depending on their activation pattern, pDC responses may be either protective or detrimental to the host. Here, we summarize and discuss current knowledge regarding pDC implication in the physiopathology of mouse and human herpesvirus infections, and we discuss how pDC functions could be manipulated in immunotherapeutic settings to promote health over disease.

Partial inhibition of human immunodeficiency virus replication by type I interferons: impact of cell-to-cell viral transfer

Type I interferons (IFN) inhibit several steps of the human immunodeficiency virus type 1 (HIV) replication cycle. Some HIV proteins, like Vif and Vpu, directly counteract IFN-induced restriction factors. Other mechanisms are expected to modulate the extent of IFN inhibition. Here, we studied the impact of IFN on various aspects of HIV replication in primary T lymphocytes. We confirm the potent effect of IFN on Gag p24 production in supernatants. Interestingly, IFN had a more limited effect on HIV spread, measured as the appearance of Gag-expressing cells. Primary isolates displayed similar differences in the inhibition of p24 release and virus spread. Virus emergence was the consequence of suboptimal inhibition of HIV replication and was not due to the selection of resistant variants. Cell-to-cell HIV transfer, a potent means of virus replication, was less sensitive to IFN than infection by cell-free virions. These results suggest that IFN are less active in cell cultures than initially thought. They help explain the incomplete protection by naturally secreted IFN during HIV infection and the unsatisfactory outcome of IFN treatment in HIV-infected patients.

Dendritic cell anergy results from endotoxemia in severe malnutrition

Malnutrition predicts an increased risk of morbidity and mortality from infection. Defects in cell-mediated immunity, such as thymic atrophy, impaired cutaneous tuberculin responses, and reduced T cell mitogenesis in vitro, are well characterized. There has been no convincing mechanism proposed for these T cell defects. However, as T cell responses rely on signals received from APCs, this study evaluates dendritic cell (DC) function in children with severe malnutrition. Repeated sampling of peripheral blood from 81 severely malnourished children at the University Teaching Hospital, Lusaka, Zambia, demonstrated for the first time a defect in DC numbers in children with malnutrition (28 per microliter) and a recovery in cell number (48 per microliter; p < 0.01) with standard treatment. We describe normal DC maturation in the majority of malnourished children. However, in 17% of our study patients, in association with endotoxemia we describe the novel finding of DC maturation failure (down-regulation rather than up-regulation of HLA-DR). There was a strong correlation between the strength of HLA-DR up or down-regulation and the generation of IL-10 (r = -0.481; p = 0.003). These "anergic" DCs failed to support T cell proliferation. Defects in DC number and the immunosuppressive phenotype of DCs from severely malnourished children with endotoxemia provide a rational basis for the anergy found in severe malnutrition.

ADAR1 interacts with PKR during human immunodeficiency virus infection of lymphocytes and contributes to viral replication

The interferon-induced protein kinase RNA activated (PKR) is activated after virus infection. This activation is transient during the human immunodeficiency virus type 1 (HIV-1) infection of lymphocytes, and the protein is not activated at the peak of infection. We observed that interferon-induced adenosine deaminase acting on RNA 1-p150 (ADAR1-p150) and ADAR1-p110 expression increases while the virus replicates actively. Furthermore, both forms of ADAR1 show enhanced interactions with PKR at the peak of HIV infection, suggesting a role for this protein in the regulation of PKR activation. We observed that ADAR1-p150, as previously shown for the TAR RNA binding protein (TRBP), reverses the PKR inhibition of HIV expression and production in HEK 293T cells. This activity requires the Z-DNA binding motif and the three double-stranded RNA binding domains but not the catalytic domain. In astrocytic cells, ADAR1-p150 increased HIV expression and production to an extent similar to that of TRBP. Small interfering RNAs against ADAR1-p150 moderately decreased HIV production. These results indicate that two interferon-induced proteins, ADAR1 and PKR, have antagonistic functions on HIV production. They suggest that ADAR1 and TRBP belong to a multiprotein complex that inhibits PKR during the HIV infection of lymphocytes.

Plasmacytoid dendritic cells accumulate in spleens from chronically HIV-infected patients but barely participate in interferon-α expression

We characterized the localization, phenotype, and some functions of plasmacytoid dendritic cells (pDCs) in the human spleen. pDCs were localized in the marginal zone and the periarteriolar region. Some were also found in the red pulp. pDCs were immature by phenotypic labeling, consistently with their capacity to internalize Dextran in a functional assay. In spleens from HIV-infected patients with thrombocytopenic purpura, these characteristics were unaffected. However, an accumulation of pDCs, but not myeloid dendritic cells (mDCs), was observed in some HIV+ patients, correlating with high proviral loads. Moreover, although undetectable in most HIV− patients, interferon-α (IFN-α) production was evidenced in situ and by flow cytometry in most HIV+ patients. IFN-α was located in the marginal zone. Surprisingly, IFN-α colocalized only with few pDCs, but rather with other cells, including T and B lymphocytes, mDCs, and macrophages. Therefore, pDCs accumulated in spleens from HIV+ patients with high proviral loads, but they did not seem to be the main IFN-α producers.

Rapid influx and death of plasmacytoid dendritic cells in lymph nodes mediate depletion in acute simian immunodeficiency virus infection

Plasmacytoid dendritic cells (pDC) are essential innate immune system cells that are lost from the circulation in human immunodeficiency virus (HIV)-infected individuals associated with CD4(+) T cell decline and disease progression. pDC depletion is thought to be caused by migration to tissues or cell death, although few studies have addressed this directly. We used precise methods of enumeration and in vivo labeling with 5-bromo-2'-deoxyuridine to track recently divided pDC in blood and tissue compartments of monkeys with acute pathogenic simian immunodeficiency virus (SIV) infection. We show that pDC are lost from blood and peripheral lymph nodes within 14 days of infection, despite a normal frequency of pDC in bone marrow. Paradoxically, pDC loss masked a highly dynamic response characterized by rapid pDC mobilization into blood and a 10- to 20-fold increase in recruitment to lymph nodes relative to uninfected animals. Within lymph nodes, pDC had increased levels of apoptosis and necrosis, were uniformly activated, and were infected at frequencies similar to CD4(+) T cells. Nevertheless, remaining pDC had essentially normal functional responses to stimulation through Toll-like receptor 7, with half of lymph node pDC producing both TNF-alpha and IFN-alpha. These findings reveal that cell migration and death both contribute to pDC depletion in acute SIV infection. We propose that the rapid recruitment of pDC to inflamed lymph nodes in lentivirus infection has a pathologic consequence, bringing cells into close contact with virus, virus-infected cells, and pro-apoptotic factors leading to pDC death.

Type I interferon in HIV treatment: from antiviral drug to therapeutic target

Type I interferons (IFNs) are soluble molecules that exert potent antiviral activity and are currently used for the treatment of a panel of viral infections. In the case of HIV, the use of type I IFN has had limited success, and has almost been abandoned. During the last decade, a series of studies has highlighted how HIV infection may cause overactivation of type I IFN production, which contributes to the exhaustion of the immune system and to disease progression. This review describes the transition from the proposed use of type I IFN as antiviral drugs in HIV infection, to the idea that blocking their activity or production may provide an immunologic benefit of much greater importance than their antiviral activity.

A frequent functional toll-like receptor 7 polymorphism is associated with accelerated HIV-1 disease progression

OBJECTIVES

Toll-like receptors (TLRs) play an important role in the innate immune response to pathogens. TLR7 recognizes RNA of various viruses including HIV. The objective of this study was to examine the influence of individual genetic variations of TLR7 on the susceptibility to and progression of HIV disease.

METHOD

We genotyped a population of 734 HIV-positive adults and 545 healthy controls for three TLR7 single nucleotide polymorphisms. The frequency of TLR7 genetic variations was assessed and related to HIV disease progression. Furthermore, we analyzed peripheral blood mononuclear cells obtained from healthy individuals differing in their TLR7 genotype and assessed their response to a TLR7-specific ligand ex vivo.

RESULTS

Presence of the most frequent TLR7 polymorphism, TLR7 Gln11Leu, was associated with higher viral loads and accelerated progression to advanced immune suppression in HIV patients. Furthermore, in women this polymorphism may be associated with increased HIV-1 susceptibility as it was found more frequently among patients as compared with controls. Peripheral blood mononuclear cells from polymorphism carriers secreted significantly less IFN-alpha following TLR7 activation, whereas IL-6 production remained unaltered.

CONCLUSION

This is the first report of a functional TLR7 variant to be associated with susceptibility to and a more severe clinical course of HIV-1 disease. These results may have implications for the risk assessment of individual patients as well as for HIV-1 therapy and vaccination strategies in the future.

Immune dysregulation in human immunodeficiency virus infection: know it, fix it, prevent it?

Infection of humans by the human immunodeficiency virus (HIV) causes a progressive, multifactorial impairment of the immune system eventually leading to the acquired immunodeficiency syndrome (AIDS). No cure or vaccine exists yet against HIV infection. More worrisome is the fact that despite having identified HIV as the cause of the AIDS, we still do not understand what pathogenic mechanisms lead to the debacle of the immune system. In this review we consider the extent and the limits of our knowledge of HIV pathogenesis, and how this knowledge may be used to design preventive and therapeutic approaches.

HIV-activated human plasmacytoid DCs induce Tregs through an indoleamine 2,3-dioxygenase-dependent mechanism

Plasmacytoid DCs (pDCs) have been implicated as crucial cells in antiviral immune responses. On recognizing HIV, they become activated, secreting large amounts of IFN-alpha and inflammatory cytokines, thereby potentiating innate and adaptive antiviral immune responses. Here, we have shown that HIV-stimulated human pDCs can also induce the differentiation of naive CD4+ T cells into Tregs with suppressive function. This differentiation was independent of pDC production of IFN-alpha and primarily dependent on pDC expression of indoleamine 2,3-dioxygenase, which was induced through the TLR/MyD88 pathway, following binding of HIV to CD4 and triggering of TLR7 by HIV genomic RNA. Functionally, the Tregs induced by pDCs were shown to inhibit the maturation of bystander conventional DCs. This study therefore reveals what we believe to be a novel mechanism by which pDC may regulate and potentially limit anti-HIV immune responses.