Human immature Langerhans cells restrict CXCR4-using HIV-1 transmission

Dengue Virus Infects Human Skin Langerhans Cells through Langerin for Dissemination to Dendritic Cells

Dengue virus (DENV) is the most disease-causative flavivirus worldwide. DENV as a mosquito-borne virus infects human hosts through the skin; however, the initial target cells in the skin remain unclear. In this study, we have investigated whether epidermal Langerhans cells (LCs) play a role in DENV acquisition and dissemination. We have used a human epidermal ex vivo infection model as well as isolated LCs to investigate infection by DENV. Notably, both immature and mature LCs were permissive to DENV infection in vitro and ex vivo, and infection was dependent on C-type lectin receptor langerin because blocking antibodies against langerin significantly reduced DENV infection in vitro and ex vivo. DENV-infected LCs efficiently transmitted DENV to target cells such as dendritic cells. Moreover, DENV exposure increased the migration of LCs from epidermal explants. These results strongly suggest that DENV targets epidermal LCs for infection and dissemination in the human host. These findings could provide potential drug targets to combat the early stage of DENV infection.

Spermine and spermidine bind CXCR4 and inhibit CXCR4- but not CCR5-tropic HIV-1 infection

Semen is an important vector for sexual HIV-1 transmission. Although CXCR4-tropic (X4) HIV-1 may be present in semen, almost exclusively CCR5-tropic (R5) HIV-1 causes systemic infection after sexual intercourse. To identify factors that may limit sexual X4-HIV-1 transmission, we generated a seminal fluid-derived compound library and screened it for antiviral agents. We identified four adjacent fractions that blocked X4-HIV-1 but not R5-HIV-1 and found that they all contained spermine and spermidine, abundant polyamines in semen. We showed that spermine, which is present in semen at concentrations up to 14 mM, binds CXCR4 and selectively inhibits cell-free and cell-associated X4-HIV-1 infection of cell lines and primary target cells at micromolar concentrations. Our findings suggest that seminal spermine restricts sexual X4-HIV-1 transmission.

Immune activation of vaginal human Langerhans cells increases susceptibility to HIV-1 infection

Vaginal inflammation increases the risk for sexual HIV-1 transmission but underlying mechanisms remain unclear. In this study we assessed the impact of immune activation on HIV-1 susceptibility of primary human vaginal Langerhans cells (LCs). Vaginal LCs isolated from human vaginal tissue expressed a broad range of TLRs and became activated after exposure to both viral and bacterial TLR ligands. HIV-1 replication was restricted in immature vaginal LCs as only low levels of infection could be detected. Notably, activation of immature vaginal LCs by bacterial TLR ligands increased HIV-1 infection, whereas viral TLR ligands were unable to induce HIV-1 replication in vaginal LCs. Furthermore, mature vaginal LCs transmitted HIV-1 to CD4 T cells. This study emphasizes the role for vaginal LCs in protection against mucosal HIV-1 infection, which is abrogated upon activation. Moreover, our data suggest that bacterial STIs can increase the risk of HIV-1 acquisition in women.

Transmission of Zika virus by dendritic cell subsets in skin and vaginal mucosa

Zika virus is a member of the Flaviviridae family that has caused recent outbreaks associated with neurological malformations. Transmission of Zika virus occurs primarily via mosquito bite but also via sexual contact. Dendritic cells (DCs) and Langerhans cells (LCs) are important antigen presenting cells in skin and vaginal mucosa and paramount to induce antiviral immunity. To date, little is known about the first cells targeted by Zika virus in these tissues as well as subsequent dissemination of the virus to other target cells. We therefore investigated the role of DCs and LCs in Zika virus infection. Human monocyte derived DCs (moDCs) were isolated from blood and primary immature LCs were obtained from human skin and vaginal explants. Zika virus exposure to moDCs but not skin and vaginal LCs induced Type I Interferon responses. Zika virus efficiently infected moDCs but neither epidermal nor vaginal LCs became infected. Infection of a human full skin model showed that DC-SIGN expressing dermal DCs are preferentially infected over langerin+ LCs. Notably, not only moDCs but also skin and vaginal LCs efficiently transmitted Zika virus to target cells. Transmission by LCs was independent of direct infection of LCs. These data suggest that DCs and LCs are among the first target cells for Zika virus not only in the skin but also the genital tract. The role of vaginal LCs in dissemination of Zika virus from the vaginal mucosa further emphasizes the threat of sexual transmission and supports the investigation of prophylaxes that go beyond mosquito control.

Antigen transfer and its effect on vaccine-induced immune amplification and tolerance

Antigen transfer refers to the process of intercellular information exchange, where antigenic components including nucleic acids, antigen proteins/peptides and peptide-major histocompatibility complexes (p-MHCs) are transmitted from donor cells to recipient cells at the thymus, secondary lymphoid organs (SLOs), intestine, allergic sites, allografts, pathological lesions and vaccine injection sites via trogocytosis, gap junctions, tunnel nanotubes (TNTs), or extracellular vesicles (EVs). In the context of vaccine inoculation, antigen transfer is manipulated by the vaccine type and administration route, which consequently influences, even alters the immunological outcome, i.e., immune amplification and tolerance. Mainly focused on dendritic cells (DCs)-based antigen receptors, this review systematically introduces the biological process, molecular basis and clinical manifestation of antigen transfer.

Infection and transmission of SARS-CoV-2 depend on heparan sulfate proteoglycans

The current pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and outbreaks of new variants highlight the need for preventive treatments. Here, we identified heparan sulfate proteoglycans as attachment receptors for SARS-CoV-2. Notably, neutralizing antibodies against SARS-CoV-2 isolated from COVID-19 patients interfered with SARS-CoV-2 binding to heparan sulfate proteoglycans, which might be an additional mechanism of antibodies to neutralize infection. SARS-CoV-2 binding to and infection of epithelial cells was blocked by low molecular weight heparins (LMWH). Although dendritic cells (DCs) and mucosal Langerhans cells (LCs) were not infected by SARS-CoV-2, both DC subsets efficiently captured SARS-CoV-2 via heparan sulfate proteoglycans and transmitted the virus to ACE2-positive cells. Notably, human primary nasal cells were infected by SARS-CoV-2, and infection was blocked by pre-treatment with LMWH. These data strongly suggest that heparan sulfate proteoglycans are important attachment receptors facilitating infection and transmission, and support the use of LMWH as prophylaxis against SARS-CoV-2 infection.

Abortive HIV-1 RNA induces pro-IL-1β maturation via protein kinase PKR and inflammasome activation in humans

The proinflammatory cytokine IL-1β mediates high levels of immune activation observed during acute and chronic human immunodeficiency virus 1 (HIV-1) infection. Little is known about the mechanisms that drive IL-1β activation during HIV-1 infection. Here, we have identified a crucial role for abortive HIV-1 RNAs in inducing IL-1β in humans. Abortive HIV-1 RNAs were sensed by protein kinase RNA-activated (PKR), which triggered activation of the canonical NLRP3 inflammasome and caspase-1, leading to pro-IL-1β processing and secretion. PKR activated the inflammasome via ROS generation and MAP kinases ERK1/2, JNK, and p38. Inhibition of PKR during HIV-1 infection blocked IL-1β production. As abortive HIV-1 RNAs are produced during productive infection and latency, our data strongly suggest that targeting PKR signaling might attenuate immune activation during acute and chronic HIV-1 infection.

Mucosal Dendritic Cell Subsets Control HIV-1's Viral Fitness

Dendritic cell (DC) subsets are abundantly present in genital and intestinal mucosal tissue and are among the first innate immune cells that encounter human immunodeficiency virus type 1 (HIV-1) after sexual contact. Although DCs have specific characteristics that greatly enhance HIV-1 transmission, it is becoming evident that most DC subsets also have virus restriction mechanisms that exert selective pressure on the viruses during sexual transmission. In this review we discuss the current concepts of the immediate events following viral exposure at genital mucosal sites that lead to selection of specific HIV-1 variants called transmitted founder (TF) viruses. We highlight the importance of the TF HIV-1 phenotype and the role of different DC subsets in establishing infection. Understanding the biology of HIV-1 transmission will contribute to the design of novel treatment strategies preventing HIV-1 dissemination.

Mathematical analysis of multi-target cells and multi-strain age-structured model with two HIV infection routes

In this paper, we propose detailed and reasonable viral dynamics by using a multi-compartment model that incorporating the age since the infection of multiple infected cells, multiple target cells (Langerhans-cells and CD4[Formula: see text] T-cells), multiple viral strains (CCR5 and CXR4 HIV) and multiple infection routes (cell-to-cell and cell-to-virus). The basic reproduction number, [Formula: see text], of the whole model is derived from two transmission mechanisms: one is the potential trigger from the infection routes for a single target cell and other is the joint effect of multiple viral infections for multi-target cells. Accordingly, we study the global stability of the steady states for the single target model. For the whole model, we prove that the infection-free steady state is globally asymptotically stable if [Formula: see text], whereas viruses persist uniformly if [Formula: see text]. Numerical simulations are carried out to illustrate the theoretical results. Sensitive analyses expound the effect of model parameters on the comprehensive reproduction number. It is remarkable to find that simultaneous control of HIV infection for two target cells can effectively reduce the viral loads within-host. Finally, our work suggests that the synergetic mechanism of multi-target cells and multi-strain cannot be ignored during treatment.

Autophagy-enhancing drugs limit mucosal HIV-1 acquisition and suppress viral replication ex vivo

Current direct-acting antiviral therapies are highly effective in suppressing HIV-1 replication. However, mucosal inflammation undermines prophylactic treatment efficacy, and HIV-1 persists in long-lived tissue-derived dendritic cells (DCs) and CD4+ T cells of treated patients. Host-directed strategies are an emerging therapeutic approach to improve therapy outcomes in infectious diseases. Autophagy functions as an innate antiviral mechanism by degrading viruses in specialized vesicles. Here, we investigated the impact of pharmaceutically enhancing autophagy on HIV-1 acquisition and viral replication. To this end, we developed a human tissue infection model permitting concurrent analysis of HIV-1 cellular targets ex vivo. Prophylactic treatment with autophagy-enhancing drugs carbamazepine and everolimus promoted HIV-1 restriction in skin-derived CD11c+ DCs and CD4+ T cells. Everolimus also decreased HIV-1 susceptibility to lab-adapted and transmitted/founder HIV-1 strains, and in vaginal Langerhans cells. Notably, we observed cell-specific effects of therapeutic treatment. Therapeutic rapamycin treatment suppressed HIV-1 replication in tissue-derived CD11c+ DCs, while all selected drugs limited viral replication in CD4+ T cells. Strikingly, both prophylactic and therapeutic treatment with everolimus or rapamycin reduced intestinal HIV-1 productive infection. Our findings highlight host autophagy pathways as an emerging target for HIV-1 therapies, and underscore the relevancy of repurposing clinically-approved autophagy drugs to suppress mucosal HIV-1 replication.

HIV-1 subverts the complement system in semen to enhance viral transmission

Semen is important in determining HIV-1 susceptibility but it is unclear how it affects virus transmission during sexual contact. Mucosal Langerhans cells (LCs) are the first immune cells to encounter HIV-1 during sexual contact and have a barrier function as LCs are restrictive to HIV-1. As semen from people living with HIV-1 contains complement-opsonized HIV-1, we investigated the effect of complement on HIV-1 dissemination by human LCs in vitro and ex vivo. Notably, pre-treatment of HIV-1 with semen enhanced LC infection compared to untreated HIV-1 in the ex vivo explant model. Infection of LCs and transmission to target cells by opsonized HIV-1 was efficiently inhibited by blocking complement receptors CR3 and CR4. Complement opsonization of HIV-1 enhanced uptake, fusion, and integration by LCs leading to an increased transmission of HIV-1 to target cells. However, in the absence of both CR3 and CR4, C-type lectin receptor langerin was able to restrict infection of complement-opsonized HIV-1. These data suggest that complement enhances HIV-1 infection of LCs by binding CR3 and CR4, thereby bypassing langerin and changing the restrictive nature of LCs into virus-disseminating cells. Targeting complement factors might be effective in preventing HIV-1 transmission.

Immune activation correlates with and predicts CXCR4 co-receptor tropism switch in HIV-1 infection

HIV-1 cell entry is mediated by binding to the CD4-receptor and chemokine co-receptors CCR5 (R5) or CXCR4 (X4). R5-tropic viruses are predominantly detected during early infection. A switch to X4-tropism often occurs during the course of infection. X4-tropism switching is strongly associated with accelerated disease progression and jeopardizes CCR5-based HIV-1 cure strategies. It is unclear whether host immunological factors play a causative role in tropism switching. We investigated the relationship between immunological factors and X4-tropism in a cross-sectional study in HIV-1 subtype C (HIV-1C)-infected patients and in a longitudinal HIV-1 subtype B (HIV-1B) seroconverter cohort. Principal component analysis identified a cluster of immunological markers (%HLA-DR⁺ CD4⁺ T-cells, %CD38⁺HLA-DR⁺ CD4⁺ T-cells, %CD38⁺HLA-DR⁺ CD8⁺ T-cells, %CD70⁺ CD4⁺ T-cells, %CD169⁺ monocytes, and absolute CD4⁺ T-cell count) in HIV-1C patients that was independently associated with X4-tropism (aOR 1.044, 95% CI 1.003–1.087, p = 0.0392). Analysis of individual cluster contributors revealed strong correlations of two markers of T-cell activation (%HLA-DR⁺ CD4⁺ T-cells, %HLA-DR⁺CD38⁺ CD4⁺ T-cells) with X4-tropism, both in HIV-1C patients (p = 0.01;p = 0.03) and HIV-1B patients (p = 0.0003;p = 0.0001). Follow-up data from HIV-1B patients subsequently revealed that T-cell activation precedes and independently predicts X4-tropism switching (aHR 1.186, 95% CI 1.065–1.321, p = 0.002), providing novel insights into HIV-1 pathogenesis and CCR5-based curative strategies.

Syndecan 4 Upregulation on Activated Langerhans Cells Counteracts Langerin Restriction to Facilitate Hepatitis C Virus Transmission

Sexually transmitted Hepatitis C virus (HCV) infections and high reinfections are a major concern amongst men who have sex with men (MSM) living with HIV-1 and HIV-negative MSM. Immune activation and/or HIV-1 coinfection enhance HCV susceptibility via sexual contact, suggesting that changes in immune cells or external factors are involved in increased susceptibility. Activation of anal mucosal Langerhans cells (LCs) has been implicated in increased HCV susceptibility as activated but not immature LCs efficiently retain and transmit HCV to other cells. However, the underlying molecular mechanism of transmission remains unclear. Here we identified the Heparan Sulfate Proteoglycan Syndecan 4 as the molecular switch, controlling HCV transmission by LCs. Syndecan 4 was highly upregulated upon activation of LCs and interference with Heparan Sulfate Proteoglycans or silencing of Syndecan 4 abrogated HCV transmission. These data strongly suggest that Syndecan 4 mediates HCV transmission by activated LCs. Notably, our data also identified the C-type lectin receptor langerin as a restriction factor for HCV infection and transmission. Langerin expression abrogated HCV infection in HCV permissive cells, whereas langerin expression on the Syndecan 4 expressing cell line strongly decreased HCV transmission to a target hepatoma cell line. These data suggest that the balanced interplay between langerin restriction and Syndecan 4 transmission determines HCV dissemination. Silencing of langerin enhanced HCV transmission whereas silencing Syndecan 4 on activated LCs decreased transmission. Blocking Heparan Sulfate Proteoglycans abrogated HCV transmission by LCs ex vivo identifying Heparan Sulfate Proteoglycans and Syndecan 4 as potential targets to prevent sexual transmission of HCV. Thus, our data strongly suggest that the interplay between receptors promotes or restricts transmission and further indicate that Syndecan 4 is the molecular switch controlling HCV susceptibility after sexual contact.

Sexually transmitted founder HIV-1 viruses are relatively resistant to Langerhans cell-mediated restriction

A single HIV-1 variant establishes infection of the host after sexual contact. Identifying the phenotypic characteristics of these Transmitted Founder (T/F) viruses is important to understand the restriction mechanisms during transmission. Langerhans cells (LCs) are the mucosal dendritic cell subset that has been shown to have a protective role in HIV-1 transmission. Immature LCs efficiently capture and degrade HIV-1 via langerin-mediated restriction. Here we have investigated the capacity of T/F HIV-1 strains to infect mucosal Langerhans cells (LCs). Notably, most T/F variants efficiently infected immature LCs derived from skin and vaginal tissue in contrast to chronic HIV-1 laboratory strains. Next we screened a panel of T/F viruses and their matched 6-month consensus sequence viruses. Interestingly most T/F variants infected immature LCs whereas donor-matched 6-month consensus sequence viruses had lost the ability to infect LCs. However, we also identified 6-month consensus sequence viruses that had retained an ability to infect LCs similar to that of the donor-matched T/F virus. Moreover, some T/F viruses and 6-month consensus sequence viruses were unable to infect immature LCs. Further analyses indicated that T/F viruses are less sensitive to langerin-mediated restriction. These data suggest that T/F HIV-1 variants have the ability to infect immature LCs, which will facilitate transmission.

New HIV-1 circulating recombinant form 94: from phylogenetic detection of a large transmission cluster to prevention in the age of geosocial-networking apps in France, 2013 to 2017

BackgroundEnding the HIV pandemic must involve new tools to rapidly identify and control local outbreaks and prevent the emergence of recombinant strains with epidemiological advantages.AimThis observational study aimed to investigate in France a cluster of HIV-1 cases related to a new circulating recombinant form (CRF). The confirmation this CRF's novelty as well as measures to control its spread are presented.MethodsPhylogenetic analyses of HIV sequences routinely generated for drug resistance genotyping before 2018 in French laboratories were employed to detect the transmission chain. The CRF involved was characterised by almost full-length viral sequencing for six cases. Cases' clinical data were reviewed. Where possible, epidemiological information was collected with a questionnaire.ResultsThe transmission cluster comprised 49 cases, mostly diagnosed in 2016-2017 (n = 37). All were infected with a new CRF, CRF94_cpx. The molecular proximity of this CRF to X4 strains and the high median viraemia, exceeding 5.0 log₁₀ copies/mL, at diagnosis, even in chronic infection, raise concerns of enhanced virulence. Overall, 41 cases were diagnosed in the Ile-de-France region and 45 were men who have sex with men. Among 24 cases with available information, 20 reported finding partners through a geosocial networking app. Prevention activities in the area and population affected were undertaken.ConclusionWe advocate the systematic use of routinely generated HIV molecular data by a dedicated reactive network, to improve and accelerate targeted prevention interventions. Geosocial networking apps can play a role in the spread of outbreaks, but could also deliver local targeted preventive alerts.

HIV-1 exposure and immune activation enhance sexual transmission of Hepatitis C virus by primary Langerhans cells

INTRODUCTION

The significant rise in incidence of Hepatitis C virus (HCV) infection among men-who-have-sex-with-men (MSM) living with HIV-1 suggests that HCV under specific circumstances is transmitted via sexual contact. During sexual transmission HCV has to cross the epithelial barrier to either directly enter the blood stream or indirectly via mucosal immune cells. However, the mechanisms of sexual transmission of HCV remain unclear. We investigated the role of Langerhans cells (LCs) in HCV susceptibility during sexual contact as LCs are among the first cells in mucosal tissues to encounter invading viruses.

METHODS

We investigated the phenotype of primary LCs in anal biopsies from MSM living with HIV-1. To investigate the role of primary LCs in HCV infection and transmission, we have used both isolated primary skin LCs and the ex vivo tissue transmission model.

RESULTS

Our data identified an important role for mucosal LCs in facilitating HCV transmission after HIV-1 exposure or immune activation. LCs were detected within mucosal anal tissues obtained from HIV-1 positive MSM biopsies. In order to perform functional studies, we used primary LCs from skin, which have a similar phenotype as mucosal LCs. Immature LCs were neither infected nor transmitted HCV to hepatocytes. Notably, exposure to HIV-1 significantly increased HCV transmission by LCs in the ex vivo transmission model. HIV-1 replication was crucial for the increased HCV transmission as HIV-1 inhibitors significantly reduced HIV-1-induced HCV transmission. Moreover, tissue immune activation of LCs also increased HCV transmission to target cells.

CONCLUSIONS

Thus, our data strongly indicate that HIV-1 or immune activation in MSM leads to capture of HCV by mucosal LCs, which might facilitate transmission to other cells or allow entry of HCV into the blood. This novel transmission mechanism by LCs also implicates that the activation state of LCs is an important cellular determinant for HCV susceptibility after sexual contact.

Increased Cervical CD4+CCR5+ T Cells Among Kenyan Sex Working Women Using Depot Medroxyprogesterone Acetate

Depot medroxyprogesterone acetate (DMPA) is the most common hormonal contraceptive used by women in sub-Saharan Africa, however, it has been epidemiologically associated with HIV infections. To assess whether DMPA has an effect on the number and activation of HIV target cells, this study assessed the levels and phenotype of blood- and mucosal-derived HIV target cells among women using DMPA. Thirty-five HIV uninfected women from the Pumwani Sex Worker cohort from Nairobi, Kenya were enrolled in the study (15 using DMPA and 20 not using hormonal contraception). Blood (plasma and peripheral blood mononuclear cells) and cervicovaginal (lavage, cervical cells, and ectocervical biopsies) samples were collected. Cellular phenotype and activation status were determined by flow cytometry, cytokine levels were assessed by bead array and image analysis assessed cell number and phenotype in situ. In blood, the proportion of HIV target cells and activated T cells was lower in DMPA users versus those not using hormonal contraceptives. However, analysis of cervical mononuclear cells showed that DMPA users had elevated levels of activated T cells (CD4⁺CD69⁺) and expressed lower levels of the HIV co-receptor CCR5 on a per cell basis, while tissue samples showed that in the ectocervix, DMPA users had a higher proportion of CD4⁺CCR5⁺ T cells. This study demonstrates that DMPA users had higher levels of activated T cells and HIV target cells in the genital tract. The increased pool of mucosal HIV target cells provides new biological information about the potential impact of DMPA on HIV susceptibility.

Phenotypic properties of envelope glycoproteins of transmitted HIV-1 variants from patients belonging to transmission chains

OBJECTIVE

Transmission of HIV-1 involves a bottleneck in which generally a single HIV-1 variant from a diverse viral population in the transmitting partner establishes infection in the new host. It is still unclear to what extent this event is driven by specific properties of the transmitted viruses or the result of a stochastic process. Our study aimed to better characterize this phenomenon and define properties shared by transmitted viruses.

DESIGN

We compared antigenic and functional properties of envelope glycoproteins of viral variants found during primary infection in 27 patients belonging to eight transmission chains.

METHODS

We generated pseudotyped viruses expressing Env variants of the viral quasispecies infecting each patient and compared their sensitivity to neutralization by eight human monoclonal broadly neutralizing antibodies (HuMoNAbs). We also compared their infectious properties by measuring their infectivity and sensitivity to various entry inhibitors.

RESULTS

Transmitted viruses from the same transmission chain shared many properties, including similar neutralization profiles, sensitivity to inhibitors, and infectivity, providing evidence that the transmission bottleneck is mainly nonstochastic. Transmitted viruses were CCR5-tropic, sensitive to MVC, and resistant to soluble forms of CD4, irrespective of the cluster to which they belonged. They were also sensitive to HuMoNAbs that target V3, the CD4-binding site, and the MPER region, suggesting that the loss of these epitopes may compromise their capacity to be transmitted.

CONCLUSION

Our data suggest that the transmission bottleneck is governed by selective forces. How these forces confer an advantage to the transmitted virus has yet to be determined.

HIV-1 replicates and persists in vaginal epithelial dendritic cells

HIV-1 acquisition occurs most commonly after sexual contact. To establish infection, HIV-1 must infect cells that support high-level replication, namely CD4⁺ T cells, which are absent from the outermost genital epithelium. Dendritic cells (DCs), present in mucosal epithelia, potentially facilitate HIV-1 acquisition. We show that vaginal epithelial DCs, termed CD1a⁺ VEDCs, are unlike other blood- and tissue-derived DCs because they express langerin but not DC-SIGN, and unlike skin-based langerin⁺ DC subset Langerhans cells (LCs), they do not harbor Birbeck granules. Individuals primarily acquire HIV-1 that utilizes the CCR5 receptor (termed either R5 or R5X4) during heterosexual transmission, and the mechanism for the block against variants that only use the CXCR4 receptor (classified as X4) remains unclear. We show that X4 as compared with R5 HIV-1 shows limited to no replication in CD1a⁺ VEDCs. This differential replication occurs after fusion, suggesting that receptor usage influences postentry steps in the virus life cycle. Furthermore, CD1a⁺ VEDCs isolated from HIV-1–infected virologically suppressed women harbor HIV-1 DNA. Thus, CD1a⁺ VEDCs are potentially infected early during heterosexual transmission and also retain virus during treatment. Understanding the interplay between HIV-1 and CD1a⁺ VEDCs is important for future prevention and cure strategies.

Transcriptional profiling of primary endometrial epithelial cells following acute HIV-1 exposure reveals gene signatures related to innate immunity

PROBLEM

Genital epithelial cells (GECs) line the mucosal surface of the female genital tract (FGT) and are the first cells that interface with both commensal microbiota and sexually transmitted pathogens. Despite the protective barrier formed by GECs, the FGT is a major site of HIV-1 infection. This highlights the importance of studying the interaction of HIV-1 and GECs.

METHOD OF STUDY

Using microarray analysis, we characterized the transcriptional profile of primary endometrial GECs grown in the presence or absence of physiological levels of E2 (10^-9  mol/L) or P4 (10^-7  mol/L) following acute exposure to HIV-1 for 6 hours.

RESULTS

Acute exposure of primary endometrial GECs to HIV-1 resulted in the expression of genes related to inflammation, plasminogen activation, adhesion and diapedesis and interferon response. Interestingly, exposure to HIV-1 in the presence of E2 and P4 resulted in differential transcriptional profiles, suggesting that the response of primary endometrial GECs to HIV-1 exposure is modulated by female sex hormones.

CONCLUSION

The gene expression signature of endometrial GECs indicates that the response of these cells may be key to determining host susceptibility to HIV-1 and that sex hormones modulate these interactions. This study allows us to explore possible mechanisms that explain the hormone-mediated fluctuation of HIV-1 susceptibility in women.

Langerhans cell: exciting developments in health and disease

Langerhans cells (LCs) have been the subject of much research since their discovery in 1868. LCs belong to the subset of leucocytes called dendritic cells. They are present in the epidermis and the pilosebaceous apparatus and monitor the cutaneous environment for changes in homeostasis. During embryogenesis, a wave of yolk sac macrophages seed the fetal skin. Then, fetal liver monocytes largely replace the yolk sac macrophages and comprise the majority of adult LCs. In the presence of skin irritation, LCs process antigen and travel to regional lymph nodes to present antigen to reactive T lymphocytes. Changes in LCs' surface markers during the journey occur under the influence of cytokines. The difference in expression of surface markers and the ability to resist radiation have allowed researchers to differentiate LCs from the murine Langerin-positive dermal dendritic cells. Exciting discoveries have been made recently regarding their role in inflammatory skin diseases, cancer and HIV. New research has shown that antibodies blocking CD1a appear to mitigate inflammation in contact hypersensitivity reactions and psoriasis. While it has been established that LCs have the potential to induce effector cells of the adaptive immune system to counter oncogenesis, recent studies have demonstrated that LCs coordinate with natural killer cells to impair development of squamous cell carcinoma caused by chemical carcinogens. However, LCs may also physiologically suppress T cells and permit keratinocyte transformation and tumorigenesis. Although long known to play a primary role in the progression of HIV infection, it is now understood that LCs also possess the ability to restrict the progression of the disease. There is a pressing need to discover more about how these cells affect various aspects of health and disease; new information gathered thus far seems promising and exciting.

Modelling coupled within host and population dynamics of [Formula: see text] and [Formula: see text] HIV infection

Most existing models have considered the immunological processes occurring within the host and the epidemiological processes occurring at population level as decoupled systems. We present a new model using continuous systems of non linear ordinary differential equations by directly linking the within host dynamics capturing the interactions between Langerhans cells, CD4[Formula: see text] T-cells, R5 HIV and X4 HIV and the without host dynamics of a basic compartmental HIV/AIDS model. The model captures the biological theories of the cells that take part in HIV transmission. The study incorporates in its analysis the differences in time scales of the fast within host dynamics and the slow without host dynamics. In the mathematical analysis, important thresholds, the reproduction numbers, were computed which are useful in predicting the progression of the infection both within the host and without the host. The study results showed that the model exhibits four within host equilibrium points inclusive of three endemic equilibria whose effects translate into different scenarios at the population level. All the endemic equilibria were shown to be globally stable using Lyapunov functions and this is an important result in linking the within host dynamics to the population dynamics, because the disease free equilibrium point ceases to exist. The effects of linking were observed on the endemic equilibrium points of both the within host and population dynamics. Linking the two dynamics was shown to increase in the viral load within the host and increase in the epidemic levels in the population dynamics.

Mucosal dendritic cells in HIV-1 susceptibility: a critical role for C-type lectin receptors

Sexual transmission is the major route of HIV-1 infection worldwide. The interaction of HIV-1 with mucosal dendritic cells (DCs) might determine HIV-1 susceptibility as well as initial antiviral immunity controlling virus in the chronic phase. Different DC subsets reside in mucosal tissues and express specific C-type lectin receptors (CLRs) that interact with HIV-1 with different outcomes. HIV-1 has been shown to subvert CLRs for viral transmission and immune evasion, whereas CLRs can also protect against HIV-1 infection. Here, we will discuss the role of CLRs in HIV-1 transmission and adaptive immunity, and how the CLRs dictate the function of DCs in infection. Ultimately, understanding the interplay between CLRs and HIV-1 will lead to targeted approaches in the search for preventative measures.

Langerhans Cells: the 'Yin and Yang' of HIV Restriction and Transmission

Langerhans cells are specialized sentinels present in the epidermis expressing Langerin, a specific C-type lectin receptor involved in HIV capture and destruction. Recently, the specific mechanism leading to this HIV restriction was discovered. Nevertheless, Langerhans cells can be infected and the way HIV escapes this restriction needs to be unraveled.

HIV-1 blocks the signaling adaptor MAVS to evade antiviral host defense after sensing of abortive HIV-1 RNA by the host helicase DDX3

The mechanisms by which human immunodeficiency virus 1 (HIV-1) avoids immune surveillance by dendritic cells (DCs), and thereby prevents protective adaptive immune responses, remain poorly understood. Here we showed that HIV-1 actively arrested antiviral immune responses by DCs, which contributed to efficient HIV-1 replication in infected individuals. We identified the RNA helicase DDX3 as an HIV-1 sensor that bound abortive HIV-1 RNA after HIV-1 infection and induced DC maturation and type I interferon responses via the signaling adaptor MAVS. Notably, HIV-1 recognition by the C-type lectin receptor DC-SIGN activated the mitotic kinase PLK1, which suppressed signaling downstream of MAVS, thereby interfering with intrinsic host defense during HIV-1 infection. Finally, we showed that PLK1-mediated suppression of DDX3-MAVS signaling was a viral strategy that accelerated HIV-1 replication in infected individuals.

Receptor usage dictates HIV-1 restriction by human TRIM5α in dendritic cell subsets

The most prevalent route of HIV-1 infection is across mucosal tissues after sexual contact. Langerhans cells (LCs) belong to the subset of dendritic cells (DCs) that line the mucosal epithelia of vagina and foreskin and have the ability to sense and induce immunity to invading pathogens. Anatomical and functional characteristics make LCs one of the primary targets of HIV-1 infection. Notably, LCs form a protective barrier against HIV-1 infection and transmission. LCs restrict HIV-1 infection through the capture of HIV-1 by the C-type lectin receptor Langerin and subsequent internalization into Birbeck granules. However, the underlying molecular mechanism of HIV-1 restriction in LCs remains unknown. Here we show that human E3-ubiquitin ligase tri-partite-containing motif 5α (TRIM5α) potently restricts HIV-1 infection of LCs but not of subepithelial DC-SIGN⁺ DCs. HIV-1 restriction by TRIM5α was thus far considered to be reserved to non-human primate TRIM5α orthologues, but our data strongly suggest that human TRIM5α is a cell-specific restriction factor dependent on C-type lectin receptor function. Our findings highlight the importance of HIV-1 binding to Langerin for the routeing of HIV-1 into the human TRIM5α-mediated restriction pathway. TRIM5α mediates the assembly of an autophagy-activating scaffold to Langerin, which targets HIV-1 for autophagic degradation and prevents infection of LCs. By contrast, HIV-1 binding to DC-SIGN⁺ DCs leads to disassociation of TRIM5α from DC-SIGN, which abrogates TRIM5α restriction. Thus, our data strongly suggest that restriction by human TRIM5α is controlled by C-type-lectin-receptor-dependent uptake of HIV-1, dictating protection or infection of human DC subsets. Therapeutic interventions that incorporate C-type lectin receptors and autophagy-targeting strategies could thus provide cell-mediated resistance to HIV-1 in humans.

Human Immunodeficiency Virus Immune Cell Receptors, Coreceptors, and Cofactors: Implications for Prevention and Treatment

In the last three decades, extensive research on human immunodeficiency virus (HIV) has highlighted its capability to exploit a variety of strategies to enter and infect immune cells. Although CD4(+) T cells are well known as the major HIV target, with infection occurring through the canonical combination of the cluster of differentiation 4 (CD4) receptor and either the C-C chemokine receptor type 5 (CCR5) or C-X-C chemokine receptor type 4 (CXCR4) coreceptors, HIV has also been found to enter other important immune cell types such as macrophages, dendritic cells, Langerhans cells, B cells, and granulocytes. Interestingly, the expression of distinct cellular cofactors partially regulates the rate in which HIV infects each distinct cell type. Furthermore, HIV can benefit from the acquisition of new proteins incorporated into its envelope during budding events. While several publications have investigated details of how HIV manipulates particular cell types or subtypes, an up-to-date comprehensive review on HIV tropism for different immune cells is lacking. Therefore, this review is meant to focus on the different receptors, coreceptors, and cofactors that HIV exploits to enter particular immune cells. Additionally, prophylactic approaches that have targeted particular molecules associated with HIV entry and infection of different immune cells will be discussed. Unveiling the underlying cellular receptors and cofactors that lead to HIV preference for specific immune cell populations is crucial in identifying novel preventative/therapeutic targets for comprehensive strategies to eliminate viral infection.

The Evolving HIV-1 Epidemic in Warao Amerindians Is Dominated by an Extremely High Frequency of CXCR4-Utilizing Strains

We previously reported a high prevalence of HIV-1 infection in Warao Amerindians from Venezuela due to the rapid spread of a single B subtype strain. In this study we evaluated the coreceptor use of the HIV-1 strains infecting this Amerindian community. Sequences of the HIV-1 V3 loop from 56 plasma samples were genotyped for coreceptor use. An extremely high frequency of CXCR4 strains was found among HIV-1-infecting Waraos (47/49, 96%), compared to HIV-1 strains infecting the non-Amerindian Venezuelan population (35/79, 44%, p < 0.00001). Evolutionary analysis showed that a significant number of infections occurred between 1 and 12 months before collection and that a great proportion (50-70%) of HIV-1 transmissions occurred within the very early phase of infection (≤12 months). This is consistent with an initial infection dominated by an X4 strain or a very rapid selection of X4 variants after infection. This Amerindian population also exhibits the highest prevalence of tuberculosis in Venezuela, being synergistically bad prognostic factors for the evolution of morbidity and mortality in this vulnerable population.

HIV-1 border patrols: Langerhans cells control antiviral responses and viral transmission

Langerhans cells (LCs) reside in the mucosal epithelia and are refractory to HIV-1 infection; HIV-1 capture by C-type lectin receptor langerin and subsequent targeting to Birbeck granules prevents infection. Furthermore, LCs restrict transmission of CXCR4-using HIV-1 variants, which underscores the role of immature LCs as gatekeepers in the selection of HIV-1 variants. Interaction of langerin on LCs with hyaluronic acid on dendritic cells facilitates cross-presentation of HIV-1 to CD8+ T cells. Activation of LCs upon inflammation bypasses the langerin-dependent barrier, which favors cross-presentation and increases susceptibility of LCs to HIV-1 infection. These recent developments not only highlight the plasticity of LCs but also define an important role for LC-dendritic cell crosstalk at the periphery in directing adaptive immune responses to viruses.

Caveolin-1 mediated uptake via langerin restricts HIV-1 infection in human Langerhans cells

Background

Human Langerhans cells (LCs) reside in foreskin and vaginal mucosa and are the first immune cells to interact with HIV-1 during sexual transmission. LCs capture HIV-1 through the C-type lectin receptor langerin, which routes the virus into Birbeck granules (BGs), thereby preventing HIV-1 infection. BGs are langerin-positive organelles exclusively present in LCs, however, their origin and function are unknown.

Results

Here, we not only show that langerin and caveolin-1 co-localize at the cell membrane and in vesicles but also that BGs are langerin/caveolin-1-positive vesicles are linked to the lysosomal degradation pathway in LCs. Moreover, inhibition of caveolar endocytosis in primary LCs abrogated HIV-1 sequestering into langerin⁺ caveolar structures. Notably, both inhibition of caveolar uptake and silencing of caveolar structure protein caveolin-1 resulted in increased HIV-1 integration and subsequent infection. In contrast, inhibition of clathrin-mediated endocytosis did not affect HIV-1 integration, even though HIV-1 uptake was decreased, suggesting that clathrin-mediated endocytosis is not involved in HIV-1 restriction in LCs.

Conclusions

Thus, our data strongly indicate that BGs belong to the caveolar endocytosis pathway and that caveolin-1 mediated HIV-1 uptake is an intrinsic restriction mechanism present in human LCs that prevents HIV-1 infection. Harnessing this particular internalization pathway has the potential to facilitate strategies to combat HIV-1 transmission.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0123-7) contains supplementary material, which is available to authorized users.

Diminished transmission of drug resistant HIV-1 variants with reduced replication capacity in a human transmission model

Background

Different patterns of drug resistance are observed in treated and therapy naïve HIV-1 infected populations. Especially the NRTI-related M184I/V variants, which are among the most frequently encountered mutations in treated patients, are underrepresented in the antiretroviral naïve population. M184I/V mutations are known to have a profound effect on viral replication and tend to revert over time in the new host. However it is debated whether a diminished transmission efficacy of HIV variants with a reduced replication capacity can also contribute to the observed discrepancy in genotypic patterns.

As dendritic cells (DCs) play a pivotal role in HIV-1 transmission, we used a model containing primary human Langerhans cells (LCs) and DCs to compare the transmission efficacy M184 variants (HIV-M184V/I/T) to HIV wild type (HIV-WT). As control, we used HIV harboring the NNRTI mutation K103N (HIV-K103N) which has a minor effect on replication and is found at a similar prevalence in treated and untreated individuals.

Results

In comparison to HIV-WT, the HIV-M184 variants were less efficiently transmitted to CCR5⁺ Jurkat T cells by both LCs and DCs. The transmission rate of HIV-K103N was slightly reduced to HIV-WT in LCs and even higher than HIV-WT in DCs. Replication experiments in CCR5⁺ Jurkat T cells revealed no apparent differences in replication capacity between the mutant viruses and HIV-WT. However, viral replication in LCs and DCs was in concordance with the transmission results; replication by the HIV-M184 variants was lower than replication by HIV-WT, and the level of replication of HIV-K103N was intermediate for LCs and higher than HIV-WT for DCs.

Conclusions

Our data demonstrate that drug resistant M184-variants display a reduced replication capacity in LCs and DCs which directly impairs their transmission efficacy. As such, diminished transmission efficacy may contribute to the lower prevalence of drug resistant variants in therapy naive individuals.