Increased Interferon Alpha Expression in Circulating Plasmacytoid Dendritic Cells of HIV-1-Infected Patients

The EBI2 receptor is coexpressed with CCR5 in CD4 + T cells and boosts HIV-1 R5 replication

OBJECTIVE

CCR5, a G protein-coupled receptor (GPCR), is used by most HIV strains as a coreceptor. In this study, we looked for other GPCR able to modify HIV-1 infection.

DESIGN

We analyzed the effects of one GPCR coexpressed with CCR5, EBI2, on HIV-1 replicative cycle.

METHODS

We identified GPCR expressed in primary CD4 + CCR5 + T cells by multi-RT-qPCR. We studied GPCR dimerization by FRET technology. Cell lines expressing EBI2 were established by transduction with HIV vectors. HIV-1 entry was quantified with virions harboring β-lactamase fused to the viral protein vpr, early and late HIV-1 transcriptions by qPCR, NFkB nuclear activation by immunofluorescence and transfection, and viral production by measuring p24 concentration in culture supernatant by ELISA.

RESULTS

We showed that EBI2 is naturally expressed in primary CD4 + CCR5 + T cells, and that CCR5 and EBI2 heterodimerize. We observed that this coexpression reduced viral entry by 50%. The amount of HIV reverse transcripts was similar in cells expressing or not EBI2. Finally, the presence of EBI2 induced the translocation of NFkB and activated HIV-1 genome expression. Globally, the result was a drastic HIV-1 R5, but not X4, overproduction in EBI2 -transduced cells.

CONCLUSION

EBI2 expression in CD4 + CCR5 + cells boosts HIV-1 R5 productive infection. As the natural ligand for EBI2 is present in blood and lymphoid tissues, the constant EBI2 activation might increase HIV replication in CD4 + T cells. It might be of interest to test the effect of EBI2 antagonists on the residual viral production persisting in patients aviremic under treatment.

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

Co-Infections and Superinfections between HIV-1 and Other Human Viruses at the Cellular Level

Co-infection or superinfection of the host by two or more virus species is a common event, potentially leading to viral interference, viral synergy, or neutral interaction. The simultaneous presence of two or more viruses, even distantly related, within the same cell depends upon viral tropism, i.e., the entry of viruses via receptors present on the same cell type. Subsequently, productive infection depends on the ability of these viruses to replicate efficiently in the same cellular environment. HIV-1 initially targets CCR5-expressing tissue memory CD4+ T cells, and in the absence of early cART initiation, a co-receptor switch may occur, leading to the infection of naïve and memory CXCR4-expressing CD4+ T cells. HIV-1 infection of macrophages at the G1 stage of their cell cycle also occurs in vivo, broadening the possible occurrence of co-infections between HIV-1 and other viruses at the cellular level. Moreover, HIV-1-infected DCs can transfer the virus to CD4+ T cells via trans-infection. This review focuses on the description of reported co-infections within the same cell between HIV-1 and other human pathogenic, non-pathogenic, or low-pathogenic viruses, including HIV-2, HTLV, HSV, HHV-6/-7, GBV-C, Dengue, and Ebola viruses, also discussing the possible reciprocal interactions in terms of virus replication and virus pseudotyping.

HIV-1 activates oxidative phosphorylation in infected CD4 T cells in a human tonsil explant model

Introduction

Human immunodeficiency virus type 1 (HIV-1) causes a chronic, incurable infection leading to immune activation and chronic inflammation in people with HIV-1 (PWH), even with virologic suppression on antiretroviral therapy (ART). The role of lymphoid structures as reservoirs for viral latency and immune activation has been implicated in chronic inflammation mechanisms. Still, the specific transcriptomic changes induced by HIV-1 infection in different cell types within lymphoid tissue remain unexplored.

Methods

In this study, we utilized human tonsil explants from healthy human donors and infected them with HIV-1 ex vivo. We performed single-cell RNA sequencing (scRNA-seq) to analyze the cell types represented in the tissue and to investigate the impact of infection on gene expression profiles and inflammatory signaling pathways.

Results

Our analysis revealed that infected CD4+ T cells exhibited upregulation of genes associated with oxidative phosphorylation. Furthermore, macrophages exposed to the virus but uninfected showed increased expression of genes associated with the NLRP3 inflammasome pathway.

Discussion

These findings provide valuable insights into the specific transcriptomic changes induced by HIV-1 infection in different cell types within lymphoid tissue. The activation of oxidative phosphorylation in infected CD4+ T cells and the proinflammatory response in macrophages may contribute to the chronic inflammation observed in PWH despite ART. Understanding these mechanisms is crucial for developing targeted therapeutic strategies to eradicate HIV-1 infection in PWH.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

Plasmacytoid dendritic cells sense HIV replication before detectable viremia following treatment interruption

Plasmacytoid dendritic cells (pDCs) are robust producers of IFNα and one of the first immune cells to respond to SIV infection. To elucidate responses to early HIV-1 replication, we studied blood pDCs in 29 HIV-infected participants who initiated antiretroviral therapy during acute infection and underwent analytic treatment interruption (ATI). We observed an increased frequency of partially activated pDCs in the blood before detection of HIV RNA. Concurrent with peak pDC frequency, we detected a transient decline in the ability of pDCs to produce IFNα in vitro, which correlated with decreased phosphorylation of IFN regulatory factory 7 (IRF7) and NF-κB. The levels of phosphorylated IRF7 and NF-κB inversely correlated with plasma IFNα2 levels, implying that pDCs were refractory to in vitro stimulation after IFNα production in vivo. After ATI, decreased expression of IFN genes in pDCs inversely correlated with the time to viral detection, suggesting that pDC IFN loss is part of an effective early immune response. These data from a limited cohort provide a critical first step in understanding the earliest immune response to HIV-1 and suggest that changes in blood pDC frequency and function can be used as an indicator of viral replication before detectable plasma viremia.

RISK6, a 6-gene transcriptomic signature of TB disease risk, diagnosis and treatment response

Improved tuberculosis diagnostics and tools for monitoring treatment response are urgently needed. We developed a robust and simple, PCR-based host-blood transcriptomic signature, RISK6, for multiple applications: identifying individuals at risk of incident disease, as a screening test for subclinical or clinical tuberculosis, and for monitoring tuberculosis treatment. RISK6 utility was validated by blind prediction using quantitative real-time (qRT) PCR in seven independent cohorts. Prognostic performance significantly exceeded that of previous signatures discovered in the same cohort. Performance for diagnosing subclinical and clinical disease in HIV-uninfected and HIV-infected persons, assessed by area under the receiver-operating characteristic curve, exceeded 85%. As a screening test for tuberculosis, the sensitivity at 90% specificity met or approached the benchmarks set out in World Health Organization target product profiles for non-sputum-based tests. RISK6 scores correlated with lung immunopathology activity, measured by positron emission tomography, and tracked treatment response, demonstrating utility as treatment response biomarker, while predicting treatment failure prior to treatment initiation. Performance of the test in capillary blood samples collected by finger-prick was noninferior to venous blood collected in PAXgene tubes. These results support incorporation of RISK6 into rapid, capillary blood-based point-of-care PCR devices for prospective assessment in field studies.

Sustained IFN-I stimulation impairs MAIT cell responses to bacteria by inducing IL-10 during chronic HIV-1 infection

Mucosal-associated invariant T (MAIT) cells in HIV-1-infected individuals are functionally impaired by poorly understood mechanisms. Single-cell transcriptional and surface protein analyses revealed that peripheral MAIT cells from HIV-1-infected subjects were highly activated with the up-regulation of interferon (IFN)-stimulated genes as compared to healthy individuals. Sustained IFN-α treatment suppressed MAIT cell responses to Escherichia coli by triggering high-level interleukin-10 (IL-10) production by monocytes, which subsequently inhibited the secretion of IL-12, a crucial costimulatory cytokine for MAIT cell activation. Blocking IFN-α or IL-10 receptors prevented MAIT cell dysfunction induced by HIV-1 exposure in vitro. Moreover, blocking the IL-10 receptor significantly improved anti-Mycobacterium tuberculosis responses of MAIT cells from HIV-1-infected patients. Our findings demonstrate the central role of the IFN-I/IL-10 axis in MAIT cell dysfunction during HIV-1 infection, which has implications for the development of anti-IFN-I/IL-10 strategies against bacterial coinfections in HIV-1-infected patients.

When Dendritic Cells Go Viral: The Role of Siglec-1 in Host Defense and Dissemination of Enveloped Viruses

Dendritic cells (DCs) are among the first cells that recognize incoming viruses at the mucosal portals of entry. Initial interaction between DCs and viruses facilitates cell activation and migration to secondary lymphoid tissues, where these antigen presenting cells (APCs) prime specific adaptive immune responses. Some viruses, however, have evolved strategies to subvert the migratory capacity of DCs as a way to disseminate infection systemically. Here we focus on the role of Siglec-1, a sialic acid-binding type I lectin receptor potently upregulated by type I interferons on DCs, that acts as a double edge sword, containing viral replication through the induction of antiviral immunity, but also favoring viral spread within tissues. Such is the case for distant enveloped viruses like human immunodeficiency virus (HIV)-1 or Ebola virus (EBOV), which incorporate sialic acid-containing gangliosides on their viral membrane and are effectively recognized by Siglec-1. Here we review how Siglec-1 is highly induced on the surface of human DCs upon viral infection, the way this impacts different antigen presentation pathways, and how enveloped viruses have evolved to exploit these APC functions as a potent dissemination strategy in different anatomical compartments.

USP18 is a significant driver of memory CD4 T-cell reduced viability caused by type I IFN signaling during primary HIV-1 infection

The loss of Memory CD4 T-cells (Mem) is a major hallmark of HIV-1 immuno-pathogenesis and occurs early during the first months of primary infection. A lot of effort has been put into understanding the molecular mechanisms behind this loss, yet they still have not been fully identified. In this study, we unveil the unreported role of USP18 in the deleterious effects of sustained type I IFN signaling on Mem, including HIV-1-specific CD4 T-cells. We find that interfering with IFN-I signaling pathway in infected patients, notably by targeting the interferon-stimulated gene USP18, resulted in reduced PTEN expression similar to those observed in uninfected control donors. We show that AKT activation in response to cytokine treatment, T-cell receptor (TcR) triggering, as well as HIV-1 Gag stimulation was significantly improved in infected patients when PTEN or USP18 were inhibited. Finally, our data demonstrate that higher USP18 in Mem from infected patients prevent proper cell survival and long-lasting maintenance in an AKT-dependent manner. Altogether, we establish a direct role for type I IFN/USP18 signaling in the maintenance of total and virus-specific Mem and provide a new mechanism for the reduced survival of these populations during primary HIV-1 infection.

In this study, we expend our knowledge of how type I interferons (IFN-I) leads to memory CD4 T-cell defective survival by unveiling the molecular mechanism behind such impairments, placing USP18 at its center. Our data further deciphers the specific USP18-related mechanism that is responsible for such impairments by implicating AKT inhibition in a PTEN-dependent manner. Our findings also point to a potential use of neutralizing anti-interferon α/β receptor antibodies to rescue the defective memory CD4 T-cell survival during HIV-1 infection, even in HIV-1 specific CD4 T-cell. To conclude, our findings provide the characterization of the molecular pathway leading to disturbances caused by sustained IFN-I signaling which occurs early during primary HIV-1 infection, complementing current knowledge which placed sustained IFN-I signaling as detrimental to the host during this infection.

Role of Dendritic Cells in Natural Immune Control of HIV-1 Infection

Dendritic cells (DCs) are professional antigen-presenting cells that link innate and adaptive immunity and are critical for the induction of protective immune responses against pathogens. Proportions of these cells are markedly decreased in the blood of untreated HIV-1-infected individuals, suggesting they might be intrinsically involved in HIV-1 pathogenesis. However, despite several decades of active research, the precise role and contribution of these cells to protective or detrimental host responses against HIV-1 are still remarkably unclear. Recent studies have shown that DCs possess a fine-tuned machinery to recognize HIV-1 replication products through a variety of innate pathogen sensing mechanisms, which may be instrumental for generating both cellular and humoral protective immune responses in persons who naturally control HIV-1 replication. Yet, dysregulated and abnormal activation of DCs might also contribute to sustained inflammation and immune activation accelerating disease progression during chronic progressive infection. Emerging data also suggest that DCs can influence the induction of potent broadly-neutralizing antibodies, and may, for this reason, have to be considered as important components of future HIV-1 vaccination strategies. Apart from their involvement in antiviral host immunity, at least a subgroup of DCs seem intrinsically susceptible to HIV-1 infection and may serve as a viral target cell population. Indeed recent studies suggest that specific DC subpopulations residing in the genital mucosa are preferentially infected by HIV-1 and play an active role in sexual transmission; therefore, DCs may contribute to viral dissemination and possible persistence of the viral reservoirs through either direct or indirect mechanisms. Here, we analyze the distinct and partially opposing roles of DCs during HIV-1 disease pathogenesis, with a focus on implications of DC biology natural immune control and HIV cure research efforts.

Expression Pattern of Individual IFNA Subtypes in Chronic HIV Infection

Interferon-α (IFN-α) plays an important role in HIV pathogenesis. IFN-α consists of 13 individual IFN-α subtypes, which exhibit individual antiviral and immunomodulatory activities in HIV infection. Here, we determined the expression profiles of all IFN-α subtypes in treated and treatment-naive HIV⁺ patients and their impact on the induction of distinct HIV restriction factors. We collected blood samples of chronic HIV⁺ patients, which underwent antiretroviral therapy or were treatment-naive, and determined the individual expression levels of different IFN-α subtypes and HIV restriction factors. HIV infection transiently enhanced the expression of IFNA mRNA. The IFN-α response was dominated by the most abundantly expressed subtypes IFNA4, A5, A7, and A14 in all individuals. HIV infection affected the expression pattern of the IFN-α response, in particular for IFNA2 and IFNA16, which were elevated by chronic HIV infection. Elevated expression of HIV restriction factors was observed in chronically HIV-infected patients, which partly decreased during successful antiretroviral treatment. In vitro stimulation of peripheral blood mononuclear cells revealed that IFN-α6, -α14, and -α21 were most effective in inducing the expression of HIV restriction factors. These results indicate that HIV infection induces a specific expression pattern of IFN-α subtypes, which in turn induce the expression of various HIV restriction factors.

The involvement of plasmacytoid cells in HIV infection and pathogenesis

Plasmacytoid dendritic cells (pDCs) are a unique dendritic cell subset that are specialized in type I interferon (IFN) production. pDCs are key players in the antiviral immune response and serve as bridge between innate and adaptive immunity. Although pDCs do not represent the main reservoir of the Human Immunodeficiency Virus (HIV), they are a crucial subset in HIV infection as they influence viral transmission, target cell infection and antigen presentation. pDCs act as inflammatory and immunosuppressive cells, thus contributing to HIV disease progression. This review provides a state of art analysis of the interactions between HIV and pDCs and their potential roles in HIV transmission, chronic immune activation and immunosuppression. A thorough understanding of the roles of pDCs in HIV infection will help to improve therapeutic strategies to fight HIV infection, and will further increase our knowledge on this important immune cell subset.

Mechanisms regulating expansion of CD8+ T cells during HIV-1 infection

Abnormal immune activation and expansion of CD8+ T cells, especially of memory and effector phenotypes, take place during HIV-1 infection, and these abnormal features persist during administration of antiretroviral therapy (ART) to infected patients. The molecular mechanisms for CD8+ T-cell expansion remain poorly characterized. In this article, we review the literature addressing features of CD8+ T-cell immune pathology and present an integrated view on the mechanisms leading to abnormal CD8+ T-cell expansion during HIV-1 infection. The expression of molecules important for directing the homing of CD8+ T cells between the circulation and lymphoid tissues, in particular CCR5 and CXCR3, is increased in CD8+ T cells in circulation and in inflamed tissues during HIV-1 infection; these disturbances in the homing capacity of CD8+ T cells have been linked to increased CD8+ T-cell proliferation. The production of IL-15, a cytokine responsible for physiological proliferation of CD8+ T cells, is increased in lymphoid tissues during HIV-1 infection as result of microbial translocation and severe inflammation. IL-15, and additional inflammatory cytokines, may lead to deregulated proliferation of CD8+ T cells and explain the accumulation of CD8+ T cells in circulation. The decreased capacity of CD8+ T cells to localize to gut-associated lymphoid tissue also contributes to the accumulation of these cells in blood. Control of inflammation, through ART administration during primary HIV-1 infection or therapies aimed at controlling inflammation during HIV-1 infection, is pivotal to prevent abnormal expansion of CD8+ T cells during HIV-1 infection.

Characterization of innate immune viral sensors in patients following allogeneic hematopoietic stem cell transplantation

Viral infection is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplant (HSCT), with up to one in four deaths directly linked to viral disease. Whilst awaiting lymphocyte reconstitution post-HSCT, the innate antiviral immune response is the first line of defense against invading viruses. Several novel innate viral-sensing pathways have recently been characterized, but their physiological importance in humans is poorly understood. We analyzed a panel of innate viral-sensor genes in HSCT patients, and assessed whether differences in innate antiviral responses could account for variation in susceptibility to viral infections. Expression levels of innate viral sensors in HSCT patients with active viral infections, HSCT patients without active infections and healthy volunteers were highly homogenous. Although IFN-α expression was up-regulated in actively infected patients relative to controls, a corresponding up-regulation of innate viral sensor expression was not observed. IFN-α stimulation of patient PBMCs in vitro showed intact IFN-α signaling, but actively infected patients' PBMCs had reduced up-regulation of innate viral sensors. We show that the aberrant IFN-α responses in HSCT patients were not due to calcineurin inhibition. Our data therefore raises the possibility of an intrinsic defect in innate viral sensor up-regulation in HSCT patients following viral infection.

Sustained IFN-I Expression during Established Persistent Viral Infection: A "Bad Seed" for Protective Immunity

Type I interferons (IFN-I) are one of the primary immune defenses against viruses. Similar to all other molecular mechanisms that are central to eliciting protective immune responses, IFN-I expression is subject to homeostatic controls that regulate cytokine levels upon clearing the infection. However, in the case of established persistent viral infection, sustained elevation of IFN-I expression bears deleterious effects to the host and is today considered as the major driver of inflammation and immunosuppression. In fact, numerous emerging studies place sustained IFN-I expression as a common nexus in the pathogenesis of multiple chronic diseases including persistent infections with the human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus (SIV), as well as the rodent-borne lymphocytic choriomeningitis virus clone 13 (LCMV clone 13). In this review, we highlight recent studies illustrating the molecular dysregulation and resultant cellular dysfunction in both innate and adaptive immune responses driven by sustained IFN-I expression. Here, we place particular emphasis on the efficacy of IFN-I receptor (IFNR) blockade towards improving immune responses against viral infections given the emerging therapeutic approach of blocking IFNR using neutralizing antibodies (Abs) in chronically infected patients.

Dendritic Cell Immune Responses in HIV-1 Controllers

PURPOSE OF REVIEW

Robust HIV-1-specific CD8 T cell responses are currently regarded as the main correlate of immune defense in rare individuals who achieve natural, drug-free control of HIV-1; however, the mechanisms that support evolution of such powerful immune responses are not well understood. Dendritic cells (DCs) are specialized innate immune cells critical for immune recognition, immune regulation, and immune induction, but their possible contribution to HIV-1 immune defense in controllers remains ill-defined.

RECENT FINDINGS

Recent studies suggest that myeloid DCs from controllers have improved abilities to recognize HIV-1 through cytoplasmic immune sensors, resulting in more potent, cell-intrinsic type I interferon secretion in response to viral infection. This innate immune response may facilitate DC-mediated induction of highly potent antiviral HIV-1-specific T cells. Moreover, protective HLA class I isotypes restricting HIV-1-specific CD8 T cells may influence DC function through specific interactions with innate myelomonocytic MHC class I receptors from the leukocyte immunoglobulin-like receptor family. Bi-directional interactions between dendritic cells and HIV-1-specific T cells may contribute to natural HIV-1 immune control, highlighting the importance of a fine-tuned interplay between innate and adaptive immune activities for effective antiviral immune defense.

Tim-3 is a Marker of Plasmacytoid Dendritic Cell Dysfunction during HIV Infection and Is Associated with the Recruitment of IRF7 and p85 into Lysosomes and with the Submembrane Displacement of TLR9

In chronic diseases, such as HIV infection, plasmacytoid dendritic cells (pDCs) are rendered dysfunctional, as measured by their decreased capacity to produce IFN-α. In this study, we identified elevated levels of T cell Ig and mucin-domain containing molecule-3 (Tim-3)-expressing pDCs in the blood of HIV-infected donors. The frequency of Tim-3-expressing pDCs correlated inversely with CD4 T cell counts and positively with HIV viral loads. A lower frequency of pDCs expressing Tim-3 produced IFN-α or TNF-α in response to the TLR7 agonists imiquimod and Sendai virus and to the TLR9 agonist CpG. Thus, Tim-3 may serve as a biomarker of pDC dysfunction in HIV infection. The source and function of Tim-3 was investigated on enriched pDC populations from donors not infected with HIV. Tim-3 induction was achieved in response to viral and artificial stimuli, as well as exogenous IFN-α, and was PI3K dependent. Potent pDC-activating stimuli, such as CpG, imiquimod, and Sendai virus, induced the most Tim-3 expression and subsequent dysfunction. Small interfering RNA knockdown of Tim-3 increased IFN-α secretion in response to activation. Intracellular Tim-3, as measured by confocal microscopy, was dispersed throughout the cytoplasm prior to activation. Postactivation, Tim-3 accumulated at the plasma membrane and associated with disrupted TLR9 at the submembrane. Tim-3-expressing pDCs had reduced IRF7 levels. Furthermore, intracellular Tim-3 colocalized with p85 and IRF7 within LAMP1⁺ lysosomes, suggestive of a role in degradation. We conclude that Tim-3 is a biomarker of dysfunctional pDCs and may negatively regulate IFN-α, possibly through interference with TLR signaling and recruitment of IRF7 and p85 into lysosomes, enhancing their degradation.

Early treatment with reverse transcriptase inhibitors significantly suppresses peak plasma IFNα in vivo during acute simian immunodeficiency virus infection

Innate interferons (IFN) are comprised of multiple Type I and III subtypes. The in vivo kinetics of subtype responses during human immunodeficiency virus (HIV) infection is not well defined. Using the acute simian immunodeficiency virus (SIV) infection model, we show that plasma IFNα levels peak at day 10 post-infection (pi) after which they rapidly declined. The mRNA expression of Type I and III IFN subtypes were significantly elevated in the lymph nodes (LN) at day 10 pi. Though the expression levels of all subtypes declined by day 14-31 pi, numerous subtypes remained elevated suggesting that ongoing viral replication in LN continues to drive induction of these subtypes. Interestingly, treatment with reverse transcriptase (RT) inhibitors at day 7 pi significantly suppressed plasma IFNα responses by day 10 pi that significantly correlated with cell-associated SIV DNA loads suggesting that RT byproducts such as viral DNA likely plays a role in driving IFN responses during acute SIV infection. Quantification of Type I and III subtype transcripts in sorted subsets of LN CD4+ and CD8+ T cells, CD14+/CD14- monocytes/macrophages, and total CD11c/CD123+ dendritic cells (DC) at day 10 pi showed that DC expressed ∼3-4 log more subtype transcripts as compared to the other subsets. Taken together, our results provide new insights into the kinetics of innate interferon responses during early stages of infection, and provide evidence that DC's are a major in vivo source of innate IFN during acute SIV infection.

Lymph nodes from HIV-infected individuals harbor mature dendritic cells and increased numbers of PD-L1+ conventional dendritic cells

The immune response induced by dendritic cells (DC) during the HIV infection has been of remarkable interest because of the therapeutic potential of DC for vaccine development. However, their beneficial or detrimental contribution in HIV infection remains unclear. The activation state of DC in lymph nodes (LN) is essential to induce T cell responses against HIV. In the present study, we characterized the immunophenotype and function of conventional (cDC) and plasmacytoid (pDC) dendritic cells from peripheral blood (PB) and LN of HIV(+) individuals. We observed that the frequency of PB pDC was decreased and exhibited an immature phenotype; whereas in the LN, activated pDC accumulated (CD40(+) and CD83(+)). In addition, the frequency of PB cDC from HIV(+) individuals was decreased and exhibited an immature phenotype, whereas LN harbored activated and mature cDC (CD40(+), CD83(+), CD80(+) and CD86(+)). However, an increased number of PD-L1(+) cDC was also observed in the LN. Moreover, pDC and cDC were able to produce inflammatory cytokines (IFN-α, TNF-α and IL-12) after TLR stimulation. These findings suggests that LN cDC expressing PD-L1 from HIV(+) individuals may negatively impact the generation of HIV-specific T cells and that DC might be contributing to tissue chronic immune activation.

In vivo effects of methamphetamine on HIV-1 replication: A population-based study

BACKGROUND

Although a number of in vitro studies have shown that methamphetamine (METH) can increase HIV-1 replication in human immune cells, a direct link between METH use and HIV-1 pathogenesis remains to be determined among HIV-1 patients.

METHODS

According to the status of METH use and HIV-1 infection, we enrolled participants and divided them into four groups: METH+HIV+, METH-HIV+, METH+HIV-, and METH-HIV-. HIV viral loads and HIV-1-related cellular factors were measured and compared among different groups.

RESULTS

A total of 60 participants were enrolled into this study, 15 within each group. HIV viral loads in METH+HIV+ group were significantly higher than those in METH-HIV+ group, while CD4+ T cell counts had an inverse trend between the two groups (p<0.05). METH users or HIV-1 infected patients had lower CCR5+, CXCR4+ percentages in CD4+ T cells than METH-HIV- subjects (p<0.01). However, METH use had little effect on CD3 expression in PBMCs and the levels of MIP-1α, MIP-1β and IL-6 in PBMCs or plasma, which were increased by HIV-1 infection with or without METH. TLR-9 and IFN-α levels in PBMCs of METH users with or without HIV infection were higher than non-METH users (p<0.05).

CONCLUSIONS

METH use is associated with higher viral loads and lower CD4+ T cell counts in HIV-infected individuals. This finding may be mediated by activation of innate immunity (TLR-9, IFN-α) by METH use.

Immune activation in the course of HIV-1 infection: Causes, phenotypes and persistence under therapy

Systemic immune activation is a striking consequence of HIV-1 infection. Even in virologically suppressed patients, some hyperactivity of the immune system and even of the endothelium and of the coagulation pathway may persist. Apart from immune deficiency, this chronic activation may contribute to various morbidities including atherothrombosis, neurocognitive disorders, liver steatosis and osteoporosis, which are currently main challenges. It is therefore of major importance to better understand the causes and the phenotypes of immune activation in the course of HIV-1 infection. In this review we will discuss the various causes of immune activation in HIV-1 infected organisms: the presence of the virus together with other microbes, eventually coming from the gut, CD4+ T cell lymphopenia, senescence and dysregulation of the immune system, and/or genetic factors. We will also describe the activation of the immune system: CD4+ and CD8+ T cells, B cells, NKT and NK cells, dendritic cells, monocytes and macrophages, and neutrophils of the inflammation cascade, as well as of the endothelium and the coagulation system. Finally, we will see that antiretroviral therapy reduces the hyperactivity of the immune and coagulation systems and the endothelial dysfunction, but often does not abolish it. A better knowledge of this phenomenon might help us to identify biomarkers predictive of non AIDS-linked comorbidities, and to define new strategies aiming at preventing their emergence.

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.

Type I IFN--a blunt spear in fighting HIV-1 infection

For more than 50 years, Type I Interferon (IFN) has been recognized as critical in controlling viral infections. IFN is produced downstream germ-line encoded pattern recognition receptors (PRRs) upon engagement by pathogen-associated molecular patterns (PAMPs). As a result, hundreds of different interferon-stimulated genes (ISGs) are rapidly induced, acting in both autocrine and paracrine manner to build a barrier against viral replication and spread. ISGs encode proteins with direct antiviral and immunomodulatory activities affecting both innate and adaptive immune responses. During infection with viruses, as HIV-1, that can establish a persistent infection, IFN although produced, is not able to block the initial infection and a chronic IFN-mediated immune activation/inflammation becomes a pathogenic mechanism of disease progression. This review will briefly summarize when and how IFN is produced during HIV-1 infection and the way this innate immune response is manipulated by the virus to its own advantage to drive chronic immune activation and progression to AIDS.

Modulation of type I interferon-associated viral sensing during acute simian immunodeficiency virus infection in African green monkeys

Natural hosts of simian immunodeficiency virus (SIV), such as African green monkeys (AGMs), do not progress to AIDS when infected with SIV. This is associated with an absence of a chronic type I interferon (IFN-I) signature. It is unclear how the IFN-I response is downmodulated in AGMs. We longitudinally assessed the capacity of AGM blood cells to produce IFN-I in response to SIV and herpes simplex virus (HSV) infection. Phenotypes and functions of plasmacytoid dendritic cells (pDCs) and other mononuclear blood cells were assessed by flow cytometry, and expression of viral sensors was measured by reverse transcription-PCR. pDCs displayed low BDCA-2, CD40, and HLA-DR expression levels during AGM acute SIV (SIVagm) infection. BDCA-2 was required for sensing of SIV, but not of HSV, by pDCs. In acute infection, AGM peripheral blood mononuclear cells (PBMCs) produced less IFN-I upon SIV stimulation. In the chronic phase, the production was normal, confirming that the lack of chronic inflammation is not due to a sensing defect of pDCs. In contrast to stimulation by SIV, more IFN-I was produced upon HSV stimulation of PBMCs isolated during acute infection, while the frequency of AGM pDCs producing IFN-I upon in vitro stimulation with HSV was diminished. Indeed, other cells started producing IFN-I. This increased viral sensing by non-pDCs was associated with an upregulation of Toll-like receptor 3 and IFN-γ-inducible protein 16 caused by IFN-I in acute SIVagm infection. Our results suggest that, as in pathogenic SIVmac infection, SIVagm infection mobilizes bone marrow precursor pDCs. Moreover, we show that SIV infection modifies the capacity of viral sensing in cells other than pDCs, which could drive IFN-I production in specific settings.

IMPORTANCE

The effects of HIV/SIV infections on the capacity of plasmacytoid dendritic cells (pDCs) to produce IFN-I in vivo are still incompletely defined. As IFN-I can restrict viral replication, contribute to inflammation, and influence immune responses, alteration of this capacity could impact the viral reservoir size. We observed that even in nonpathogenic SIV infection, the frequency of pDCs capable of efficiently sensing SIV and producing IFN-I was reduced during acute infection. We discovered that, concomitantly, cells other than pDCs had increased abilities for viral sensing. Our results suggest that pDC-produced IFN-I upregulates viral sensors in bystander cells, the latter gaining the capacity to produce IFN-I. These results indicate that in certain settings, cells other than pDCs can drive IFN-I-associated inflammation in SIV infection. This has important implications for the understanding of persistent inflammation and the establishment of viral reservoirs.

IFN-α exerts opposing effects on activation-induced and IL-7-induced proliferation of T cells that may impair homeostatic maintenance of CD4+ T cell numbers in treated HIV infection

To determine whether IFN-α is a cause of the T cell hyperactivation and IL-7 signaling pathway defects that are observed in some HIV patients receiving antiretroviral therapy, we have investigated the effect of IFN-α on the proliferation of CD4(+) and CD8(+) T cells from healthy donors (n = 30) and treated HIV(+) donors (n = 20). PBMC were cultured for 7 d with staphylococcal enterotoxin B or IL-7 in the absence or presence of 100 U/ml IFN-α8. Total and naive CD4(+) and CD8(+) T cells were assessed for proliferation (via Ki67 expression), CD127 expression, and phosphorylated STAT5 levels using flow cytometry. IFN-α significantly enhanced activation-induced proliferation (via staphylococcal enterotoxin B stimulation) but inhibited homeostatic proliferation (IL-7 induced) of CD4(+) and CD8(+) T cells. Both of these effects may adversely affect CD4(+) T cell homeostasis in HIV patients. CD127 expression was increased in both healthy and HIV(+) donors following culture with IFN-α8, and levels of IL-7-induced phosphorylated STAT5 were increased by IFN-α8 in healthy donors only. Hence, the inhibitory effects of IFN-α on IL-7-induced proliferation of CD4(+) T cells are unlikely to be mediated by downregulation of CD127 expression or inhibition of STAT5 phosphorylation. These data suggest that increased IFN-α activity may promote the loss of T cells by accelerating cell turnover and activation-induced cell death while decreasing the renewal of T cells by inhibiting the proliferative effect of IL-7.

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.

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 IFNβ 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.

Interferon-alpha, immune activation and immune dysfunction in treated HIV infection

Type I interferons (IFNs) exert anti-viral effects through the induction of numerous IFN-stimulated genes and an immunomodulatory effect on innate and adaptive immune responses. This is beneficial in controlling virus infections but prolonged IFN-α activity in persistent virus infections, such as HIV infection, may contribute to immune activation and have a detrimental effect on the function of monocytes and T and B lymphocytes. Activation of monocytes, associated with increased IFN-α activity, contributes to atherosclerotic vascular disease, brain disease and other ‘age-related diseases' in HIV patients treated with long-term antiretroviral therapy (ART). In HIV patients receiving ART, the anti-viral effects of IFN-α therapy have the potential to contribute to eradication of HIV infection while IFN-α inhibitor therapy is under investigation for the treatment of immune activation. The management of HIV patients receiving ART will be improved by understanding more about the opposing effects of IFN-α on HIV infection and disease and by developing methods to assess IFN-α activity in clinical practice.

Plasmacytoid dendritic cell dynamics tune interferon-alfa production in SIV-infected cynomolgus macaques

IFN-I production is a characteristic of HIV/SIV primary infections. However, acute IFN-I plasma concentrations rapidly decline thereafter. Plasmacytoid dendritic cells (pDC) are key players in this production but primary infection is associated with decreased responsiveness of pDC to TLR 7 and 9 triggering. IFNα production during primary SIV infection contrasts with increased pDC death, renewal and dysfunction. We investigated the contribution of pDC dynamics to both acute IFNα production and the rapid return of IFNα concentrations to pre-infection levels during acute-to-chronic transition. Nine cynomolgus macaques were infected with SIVmac251 and IFNα-producing cells were quantified and characterized. The plasma IFN-I peak was temporally associated with the presence of IFNα(+) pDC in tissues but IFN-I production was not detectable during the acute-to-chronic transition despite persistent immune activation. No IFNα(+) cells other than pDC were detected by intracellular staining. Blood-pDC and peripheral lymph node-pDC both lost IFNα(-) production ability in parallel. In blood, this phenomenon correlated with an increase in the counts of Ki67(+)-pDC precursors with no IFNα production ability. In tissues, it was associated with increase of both activated pDC and KI67(+)-pDC precursors, none of these being IFNα(+) in vivo. Our findings also indicate that activation/death-driven pDC renewal rapidly blunts acute IFNα production in vivo: pDC sub-populations with no IFNα-production ability rapidly increase and shrinkage of IFNα production thus involves both early pDC exhaustion, and increase of pDC precursors.

Immune activation and the role of TLRs and TLR agonists in the pathogenesis of HIV-1 infection in the humanized mouse model

Immune activation plays a critical role in HIV-1 pathogenesis, but the pathways that are responsible for HIV-1-associated immune activation are not well understood. Recent advances in the development of a humanized mouse model for HIV-1 infection might provide new approaches to study the mechanisms of HIV-1 associated immune activation, and to test interventions aimed at reducing HIV-1 pathogenesis.

Longitudinal analysis of distribution and function of plasmacytoid dendritic cells in peripheral blood and gut mucosa of HIV infected patients

Aberrant activation of plasmacytoid dendritic cells (pDCs) with excessive production of interferon alpha (IFNα) represents one of the hallmarks of immune activation during chronic phase of human immunodeficiency virus (HIV) infection. A number of studies have shown that disruption of mucosal integrity in the gut is a cause of persistent immune activation. However, little is known about the role that pDCs play in this process, and our current understanding comes from the simian immunodeficiency virus macaque model. Thus, in the present study we sought to investigate the frequency and function of pDCs in peripheral blood and gut samples from HIV-infected individuals before and 6 months after initiation of antiretroviral therapy (ART). We show that circulating pDCs were depleted in ART-naive HIV+ patients, and upregulated the gut-homing receptor CD103 compared with uninfected controls. By converse, pDCs accumulated in the terminal ileum of ART-naive HIV individuals compared with controls. Baseline levels of IFNα production and markers of immune activation in gut samples of ART-naive HIV subjects were elevated. All these parameters declined after 6 months of ART. Our results suggest that in chronic HIV infection, pDCs migrate from peripheral blood to the gut-associated lymphatic tissue, where they may contribute to immune activation.

Dendritic cell dysregulation during HIV-1 infection

Dendritic cells (DCs) are a diverse subset of innate immune cells that are key regulators of the host response to human immunodeficiency virus-1 (HIV-1) infection. HIV-1 directly and indirectly modulates DC function to hinder the formation of effective antiviral immunity and fuel immune activation. This review focuses upon the differential dysregulation of myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) at various stages of HIV-1 infection providing insights into pathogenesis. HIV-1 evades innate immune sensing by mDCs resulting in suboptimal maturation, lending to poor generation of antiviral adaptive responses and contributing to T-regulatory cell (Treg) development. Dependent upon the stage of HIV-1 infection, mDC function is altered in response to Toll-like receptor ligands, which further hinders adaptive immunity and limits feasibility of therapeutic vaccine strategies. pDC interactions with HIV-1 are pleotropic, modulating immune responses on an axis between immunostimulatory and immunosuppressive. pDCs promote immune activation through an altered phenotype of persistent type I interferon secretion and weak antigen presentation capacity. Conversely, HIV-1 stimulates secretion of indolemine 2,3 dioxygenase (IDO) by pDCs resulting in Treg induction. An improved understanding of the roles and underlying mechanisms of DC dysfunction will be valuable to the development of therapeutics to enhance HIV-specific adaptive responses and to dampen immune activation.

Inhibitory effects of chloroquine on the activation of plasmacytoid dendritic cells in SIVmac239-infected Chinese rhesus macaques

It is currently widely accepted that immune activation in HIV-infected individuals leads to a severe loss of CD4⁺ T cells and the progression to AIDS. However, the underlying mechanism of this immune activation remains unclear. Experimental data suggest that the activation of plasmacytoid dendritic cells (pDCs) by plasma viremia may play a critical role in HIV-induced immune activation. In this study, we found that the level of immune activation was higher in the late phase of SIVmac239 infection compared with chronic infection, which suggests that immune activation might be related to disease progression in SIVmac239-infected non-human primate models. Our work also showed that chloroquine could effectively inhibit the activation of pDCs in vitro and in vivo. However, chloroquine treatment of SIVmac239-infected macaques had no significant influence on the Cellular composition of peripheral blood in these animals.

Differential regulation of toll-like receptor pathways in acute and chronic HIV-1 infection

OBJECTIVE AND DESIGN

The objective of this study was to determine changes in toll-like receptor (TLR) responses of monocytes, myeloid dendritic cells and plasmacytoid dendritic cells during primary and chronic HIV-1 infection. TLRs serve as important innate receptors to sense pathogens, and have been implicated in mediating immune activation in HIV-1 infection. Studies assessing the consequences of HIV-1 infection on the ability of innate immune cells to respond to TLR stimulation have come to varying conclusions.

METHODS

Using intracellular flow cytometry, cytokine production by cryopreserved peripheral blood mononuclear cells from healthy controls and HIV-1-infected individuals were examined after TLR stimulation.

RESULTS

We observed that the effect of HIV-1 infection on TLR responses not only depended on the stage of HIV-1 infection, but was also dependent on the individual receptor and cell type examined. Monocyte and myeloid dendritic cell responses to TLR8 stimulation were associated with HIV-1 viral load and CD4 T-cell count, whereas plasmacytoid dendritic cell responses to TLR7 stimulation were not. Responses to TLR2 stimulation were not affected by HIV-1 infection, whereas responses to TLR9 stimulation were universally decreased in all HIV-1-infected individuals examined regardless of treatment or clinical parameters.

CONCLUSION

Responsiveness to TLR7/8 stimulation, which have been shown to recognize HIV-1 ssRNA, did not decrease in chronic infection, and may represent a contributing factor to ongoing T-cell immune activation in the setting of chronic viremic HIV-1 infection.

A plasma biomarker signature of immune activation in HIV patients on antiretroviral therapy

BACKGROUND

Immune activation is a strong predictor of disease progression in HIV infection. Combinatorial plasma biomarker signatures that represent surrogate markers of immune activation in both viremic and aviremic HIV patients on combination antiretroviral therapy (cART) have not been defined. Here, we identify a plasma inflammatory biomarker signature that distinguishes between both viremic and aviremic HIV patients on cART and healthy controls and examine relationships of this signature to markers of disease progression.

METHODS

Multiplex profiling and ELISA were used to detect 15 cytokines/chemokines, soluble IL-2R (sIL-2R), and soluble CD14 (sCD14) in plasma from 57 HIV patients with CD4 nadir <300 cells/µl and 29 healthy controls. Supervised and unsupervised analyses were used to identify biomarkers explaining variance between groups defined by HIV status or drug abuse. Relationships between biomarkers and disease markers were examined by Spearman correlation.

RESULTS

The majority (91%) of HIV subjects were on cART, with 38% having undetectable viral loads (VL). Hierarchical clustering identified a biomarker cluster in plasma consisting of two interferon-stimulated gene products (CXCL9 and CXCL10), T cell activation marker (sIL-2R), and monocyte activation marker (sCD14) that distinguished both viremic and aviremic HIV patients on cART from controls (p<0.0001) and were top-ranked in variables important in projection plots. IL-12 and CCL4 were also elevated in viremic and aviremic patients compared to controls (p<0.05). IL-12 correlated with IFNα, IFNγ, CXCL9, and sIL-2R (p<0.05). CXCL10 correlated positively with plasma VL and percentage of CD16+ monocytes, and inversely with CD4 count (p = 0.001, <0.0001, and 0.04, respectively).

CONCLUSION

A plasma inflammatory biomarker signature consisting of CXCL9, CXCL10, sIL-2R, and sCD14 may be useful as a surrogate marker to monitor immune activation in both viremic and aviremic HIV patients on cART during disease progression and therapeutic responses.

HIV infection and aging of the innate immune system

The increased life expectancy of HIV-infected individuals due to improved treatment has revealed an unexpected increase in non-AIDS comorbidities that are typically associated with older age including cardiovascular disease, dementia and frailty. The majority of these diseases arise as the result of dysregulated systemic inflammation, and both the aged and HIV-infected individuals exhibit elevated basal levels of inflammation. In the elderly, increased inflammation and age-related diseases are associated with a state of impaired immunity called immunosenescence, which is thought to result from a lifetime of immune stimulation. It is now apparent that HIV induces premature immunosenescence within T-cells; however, the impact of HIV on aging of cells of the innate arm of the immune system is unknown. Innate immune cells play a central role in inflammation and are thus critical for the pathogenesis of inflammatory diseases. Limited evidence suggests HIV infection mimics age-related changes to innate immune cells; however, the extent of this effect and the mechanism underlying these changes remain to be defined. This review focuses on the impact of HIV infection on the function and aging of innate immune cells and discusses potential drivers of premature immunosenescence including chronic endotoxaemia, residual viraemia, telomere attrition and altered cellular signalling.

Plasmacytoid dendritic cells in HIV infection

Plasmacytoid dendritic cells (pDCs) are innate immune cells that are specialized to produce interferon-alpha (IFNα) and participate in activating adaptive immune responses. Although IFNα inhibits HIV-1 (HIV) replication in vitro, pDCs may act as inflammatory and immunosuppressive dendritic cells (DCs) rather than classical antigen-presenting cells during chronic HIV infection in vivo, contributing more to HIV pathogenesis than to protection. Improved understanding of HIV-pDC interactions may yield potential new avenues of discovery to prevent HIV transmission, to blunt chronic immune activation and exhaustion, and to enhance beneficial adaptive immune responses. In this chapter we discuss pDC biology, including pDC development from progenitors, trafficking and localization of pDCs in the body, and signaling pathways involved in pDC activation. We focus on the role of pDCs in HIV transmission, chronic disease progression and immune activation, and immunosuppression through regulatory T cell development. Lastly, we discuss potential future directions for the field which are needed to strengthen our current understanding of the role of pDCs in HIV transmission and pathogenesis.

HIV-1 targeting of IFN regulatory factors

Pathogens such as HIV-1 that cause chronic infections are particularly capable at adapting to the host in a manner that ensures long-term residence, and have evolved numerous mechanisms to evade various aspects of the innate and adaptive immune response. One of these mechanisms is the targeting of members of the IFN regulatory factor family. IFN regulatory factors are transcription factors that are implicated in the regulation of a variety of biological processes, including IFN induction and immune cell activation of downstream responses triggered by Toll-like receptors and other pattern-recognition receptors. Here, we report the specific targeting by HIV-1 of this class of cellular transcription factors, and describe how HIV-1 both makes them harmless and hijacks them, profoundly affecting their activity and turning them to its own advantage in order to facilitate its replication, survival, evasion of immune responses and spread.

CD4+ T-cell deficiency in HIV patients responding to antiretroviral therapy is associated with increased expression of interferon-stimulated genes in CD4+ T cells

Most patients with human immunodeficiency virus (HIV) who remain CD4(+) T-cell deficient on antiretroviral therapy (ART) exhibit marked immune activation. As CD4(+) T-cell activation may be mediated by microbial translocation or interferon-alpha (IFN-α), we examined these factors in HIV patients with good or poor CD4(+) T-cell recovery on long-term ART. Messenger RNA levels for 3 interferon-stimulated genes were increased in CD4(+) T cells of patients with poor CD4(+) T-cell recovery, whereas levels in patients with good recovery did not differ from those in healthy controls. Poor CD4(+) T-cell recovery was also associated with CD4(+) T-cell expression of markers of activation, senescence, and apoptosis, and with increased serum levels of the lipopolysaccharide receptor and soluble CD14, but these were not significantly correlated with expression of the interferon-stimulated genes. Therefore, CD4(+) T-cell recovery may be adversely affected by the effects of IFN-α, which may be amenable to therapeutic intervention.

Preferential depletion of CD2(low) plasmacytoid dendritic cells in HIV-infected subjects

Plasmacytoid dendritic cells (pDCs) are decreased in number and are functionally impaired in HIV act reasons for pDCs depletion are still unknown. It was recently reported that pDCs can be divided into two functionally distinct populations based on their CD2 expression level. To determine how the CD2(high) and CD2(low) populations are affected by HIV infection, we analyzed their frequencies in the peripheral blood of HIV-infected subjects and healthy controls. We found that the CD2(low) pDC subset was preferentially depleted in infected individuals. The frequency of CD2(low) pDCs correlated with the CD4(+) T-cell count but not with the plasma viral load. This finding furthers our understanding of the causes and consequences of pDC depletion during HIV infection.

DCs and NK cells: critical effectors in the immune response to HIV-1

Dendritic cells (DCs) and natural killer (NK) cells have central roles in antiviral immunity by shaping the quality of the adaptive immune response to viruses and by mediating direct antiviral activity. HIV-1 infection is characterized by a severe dysregulation of the antiviral immune response that starts during early infection. This Review describes recent insights into how HIV-1 infection affects DC and NK cell function, and the roles of these innate immune cells in HIV-1 pathogenesis. The importance of understanding DC and NK cell crosstalk during HIV infection for the development of effective antiviral strategies is also discussed.

Spatiotemporal trafficking of HIV in human plasmacytoid dendritic cells defines a persistently IFN-α-producing and partially matured phenotype

Plasmacytoid DCs (pDCs) are innate immune cells that are specialized to produce IFN-α and to activate adaptive immune responses. Although IFN-α inhibits HIV-1 replication in vitro, the production of IFN-α by HIV-activated pDCs in vivo may contribute more to HIV pathogenesis than to protection. We have now shown that HIV-stimulated human pDCs allow for persistent IFN-α production upon repeated stimulation, express low levels of maturation molecules, and stimulate weak T cell responses. Persistent IFN-α production by HIV-stimulated pDCs correlated with increased levels of IRF7 and was dependent upon the autocrine IFN-α/β receptor feedback loop. Because it has been shown that early endosomal trafficking of TLR9 agonists causes strong activation of the IFN-α pathway but weak activation of the NF-κB pathway, we sought to investigate whether early endosomal trafficking of HIV, a TLR7 agonist, leads to the IFN-α-producing phenotype we observed. We demonstrated that HIV preferentially traffics to the early endosome in human pDCs and therefore skews pDCs toward a partially matured, persistently IFN-α-secreting phenotype.

Changes in inflammatory and coagulation biomarkers: a randomized comparison of immediate versus deferred antiretroviral therapy in patients with HIV infection

OBJECTIVES

Among a subgroup of participants in the Strategies for Management of Antiretroviral Therapy (SMART) Trial that were naïve to antiretroviral therapy (ART) or off ART (6 months or longer) at study entry, risk of AIDS and serious non-AIDS events were increased for participants who deferred ART compared with those randomized to (re)initiate ART immediately. Our objective was to determine whether ART initiation in this group reduced markers of inflammation and coagulation that have been associated with increased mortality risk in SMART. Changes in these biomarkers have been described after stopping ART, but not after starting ART in SMART.

METHODS

Stored specimens for 254 participants (126 drug conservation [DC] and 128 viral suppression [VS]) who were naïve to ART or off ART (6 months or longer) were analyzed for interleukin-6, high sensitivity C-reactive protein, and D-dimer at baseline and Months 2 and 6.

RESULTS

At Month 6, 62% of the VS group had HIV RNA less than 400 copies/mL and median CD4 count was 190 cells/mm3 higher than for the DC group (590 versus 400 cells/mm3). Compared with DC, the VS group had 32% (95% confidence interval, 19%-43%) lower D-dimer levels at Month 6 (P < 0.001); differences were not significant for high sensitivity C-reactive protein or interleukin-6 levels.

CONCLUSIONS

In this randomized comparison of immediate versus delayed ART initiation, D-dimer, but not interleukin-6 and high sensitivity C-reactive protein, declined significantly after starting ART. Further studies are needed to determine whether improvements in D-dimer are associated with reduced risk of clinical disease and whether adjunct treatments used in combination with ART can reduce inflammation among individuals with HIV infection.

Gaining a foothold: how HIV avoids innate immune recognition

During the first week after sexual exposure to HIV, HIV infection does not appear to trigger a strong innate immune response. Here we describe some recent studies that show that HIV may avoid triggering antiviral innate immune responses by not replicating efficiently in dendritic cells and by avoiding detection in infected CD4 T cells and macrophages by harnessing a host cytoplasmic DNase TREX1 to digest nonproductive HIV reverse transcripts.

Biomarkers and HIV-associated cardiovascular disease

PURPOSE OF REVIEW

Our goal is to summarize recent literature on biomarkers of cardiovascular disease (CVD) in the setting of HIV infection with an emphasis on those associated with clinical events.

RECENT FINDINGS

Epidemiological data have demonstrated that HIV infection is associated with increases in well established markers of inflammation and thrombosis, and levels of high sensitivity C-reactive protein, interleukin-6, and D-dimer predict CVD and mortality risk in HIV cohorts. Levels of interleukin-6, D-dimer and endothelial adhesion molecules increase when antiretroviral therapy is interrupted, suggesting that HIV replication may be driving CVD risk in this context. However, data on changes in many CVD biomarkers after starting antiretroviral therapy are inconsistent or lacking. Finally, high-density lipoprotein particles may be more informative than other lipoprotein measures for CVD risk specifically among individuals with HIV infection.

SUMMARY

Biomarkers of inflammation and thrombosis have the potential to improve CVD risk stratification beyond traditional and HIV-specific factors, and may prove useful for evaluating CVD prevention strategies for individuals with HIV infection.

Association of TRIM22 with the type 1 interferon response and viral control during primary HIV-1 infection

Type 1 interferons (IFNs) induce the expression of the tripartite interaction motif (TRIM) family of E3 ligases, but the contribution of these antiviral factors to HIV pathogenesis is not completely understood. We hypothesized that the increased expression of select type 1 IFN and TRIM isoforms is associated with a significantly lower likelihood of HIV-1 acquisition and viral control during primary HIV-1 infection. We measured IFN-α, IFN-β, myxovirus resistance protein A (MxA), human TRIM5α (huTRIM5α), and TRIM22 mRNA levels in peripheral blood mononuclear cells (PBMCs) of high-risk, HIV-1-uninfected participants and HIV-1-positive study participants. Samples were available for 32 uninfected subjects and 28 infected persons, all within 1 year of infection. HIV-1-positive participants had higher levels of IFN-β (P = 0.0005), MxA (P = 0.007), and TRIM22 (P = 0.01) and lower levels of huTRIM5α (P < 0.001) than did HIV-1-negative participants. TRIM22 but not huTRIM5α correlated positively with type 1 IFN (IFN-α, IFN-β, and MxA) (all P < 0.0001). In a multivariate model, increased MxA expression showed a significant positive association with viral load (P = 0.0418). Furthermore, TRIM22 but not huTRIM5α, IFN-α, IFN-β, or MxA showed a negative correlation with plasma viral load (P = 0.0307) and a positive correlation with CD4(+) T-cell counts (P = 0.0281). In vitro studies revealed that HIV infection induced TRIM22 expression in PBMCs obtained from HIV-negative donors. Stable TRIM22 knockdown resulted in increased HIV-1 particle release and replication in Jurkat reporter cells. Collectively, these data suggest concordance between type 1 IFN and TRIM22 but not huTRIM5α expression in PBMCs and that TRIM22 likely acts as an antiviral effector in vivo.