HIV transmitting mononuclear phagocytes; integrating the old and new

HIV-1 cell-to-cell infection of macrophages escapes type I interferon and host restriction factors, and is resistant to antiretroviral drugs

HIV-1-infected macrophages participate in viral transmission, dissemination, and establishment of tissue virus reservoirs. Despite counteracting viral proteins (Vif, Vpu, Vpr and Nef), cell-free virus macrophage infection is restricted by host cell factors, including those induced by interferons. Here, we show that these viral proteins and type I interferon do not influence HIV-1 cell-to-cell transfer to macrophages by cell-cell fusion with infected T cells, still leading to the formation of multinucleated giant cells (MGCs). Accordingly, depletion of SERINC5 and APOBEC3G do not alter virus spreading and formation of virus-producing MGCs. We further show that the nuclei derived from infected T cells remains transcriptionally active in MGCs and may explain resistance to restriction factors and antiretroviral drugs. Unexpectedly, we detect viral DNA in myeloid nuclei shortly after the initial fusion with macrophages. Together, these findings unravel how HIV-1 macrophage infection by cell-cell fusion escapes type I interferon and cellular restriction factors independently of the viral auxiliary proteins, while displaying resistance to antiretroviral drugs.

Innate lymphoid cells in HIV pathogenesis and in the human female genital tract

PURPOSE OF REVIEW

Women are underrepresented in HIV infection and prevention research despite making up half of people living with HIV. The female genital tract (FGT) serves as a primary site of HIV acquisition, but gaps in knowledge remain regarding protective innate immune mechanisms. Innate lymphoid cells are tissue-resident cells involved in mucosal barrier maintenance and protection, and innate lymphoid cells (ILCs) are altered during chronic HIV infection. However, ILCs role in mucosal HIV pathogenesis is unclear and they are poorly characterized in the FGT.

RECENT FINDINGS

Human ILCs differ from their mouse counterparts and plastically adjust to their tissue of residency. Human ILC characterization is difficult due to tissue-specific adaptations and transition between subsets. While evidence for ILC involvement in antiviral activity and barrier maintenance is provided in mouse models, human ILC role in mucosal immunity remain understudied, particularly in the FGT. In chronic HIV/simian immunodeficiency virus (SIV) infection, ILCs are altered in a tissue-specific manner, and SIV models indicate potential for antiviral responses.

SUMMARY

ILCs are tissue-resident plastic cells that provide barrier protection at mucosal surfaces and display antiviral capacity. Considering that HIV is primarily transmitted through mucosal exposure, more research is needed to understand ILC contribution to HIV pathogenesis in human mucosal surfaces relevant for HIV acquisition.

Bacterial vaginosis is associated with transcriptomic changes but not higher concentrations of cervical leukocytes in a study of women at high risk for HIV acquisition

BACKGROUND

The association between bacterial vaginosis (BV) and increased HIV acquisition risk may be related to concentrations of HIV-susceptible immune cells in the cervix.

METHODS

Participants (31 with BV and 30 with normal microbiota) underwent cervical biopsy at a single visit. Immune cells were quantified and sorted using flow cytometry (N=55), localization assessed by immunofluorescence (N=16), and function determined by bulk RNA sequencing (RNA-seq) of live CD45+ cells (N=21).

RESULTS

Linear regression analyses demonstrated no differences in mean log2 [cells/mg tissue] between women with BV vs normal microbiota for antigen presenting cell (APC) subtypes linked to HIV risk (including CD1a+HLA-DR+ Langerhans cells, CD11c+CD14+ dendritic cells [DCs], and CD11c+HLA-DR+ DCs) and CD4+ T cells. Women with BV had a higher median proportion of CD11c+HLA-DR+ APCs (out of total cells) in cervical epithelium (0.1% vs 0.0%; p=0.03 using Mann-Whitney testing). RNA-seq identified 1,032 differentially expressed genes (adjusted p-value <0.05) in CD45+ cells between women with BV vs normal microbiota. Women with BV demonstrated downregulation of pathways linked to translation, metabolism, cell stress, and immune signaling.

CONCLUSIONS

BV alters immune cell localization and function; future studies are needed to address how these changes may mediate HIV acquisition risk.

Recent Advances in Our Understanding of Human Inflammatory Dendritic Cells in Human Immunodeficiency Virus Infection

Anogenital inflammation is a critical risk factor for HIV acquisition. The primary preventative HIV intervention, pre-exposure prophylaxis (PrEP), is ineffective in blocking transmission in anogenital inflammation. Pre-existing sexually transmitted diseases (STIs) and anogenital microbiota dysbiosis are the leading causes of inflammation, where inflammation is extensive and often asymptomatic and undiagnosed. Dendritic cells (DCs), as potent antigen-presenting cells, are among the first to capture HIV upon its entry into the mucosa, and they subsequently transport the virus to CD4 T cells, the primary HIV target cells. This increased HIV susceptibility in inflamed tissue likely stems from a disrupted epithelial barrier integrity, phenotypic changes in resident DCs and an influx of inflammatory HIV target cells, including DCs and CD4 T cells. Gaining insight into how HIV interacts with specific inflammatory DC subsets could inform the development of new therapeutic strategies to block HIV transmission. However, little is known about the early stages of HIV capture and transmission in inflammatory environments. Here, we review the currently characterised inflammatory-tissue DCs and their interactions with HIV.

Massive endocytosis mechanisms are involved in uptake of HIV-1 particles by monocyte-derived dendritic cells

Introduction

HIV-1 exploits dendritic cells (DCs) to spread throughout the body via specific recognition of gangliosides present on the viral envelope by the CD169/Siglec-1 membrane receptor. This interaction triggers the internalization of HIV-1 within a structure known as the sac-like compartment. While the mechanism underlying sac-like compartment formation remains elusive, prior research indicates that the process is clathrin-independent and cell membrane cholesterol-dependent and involves transient disruption of cortical actin. Here, we investigate the potential involvement of massive endocytosis (MEND) in this process.

Methods

We used live cell confocal imaging to measure the dimensions and dynamics of the compartment. We assessed the role of actin and cholesterol in fixed and live cells using confocal microscopy and evaluated the effect of PI3K and protein palmytoilation inhibitors during viral uptake.

Results

Our data demonstrate extensive plasma membrane invagination based on sac-like compartment dimensions (2.9 μm in diameter and 20 μm3 in volume). We showed that the cholesterol concentration doubles within the regions of viral uptake, suggesting lipid-phase separation, and that development of the sac-like compartment is accompanied by transient depolarization of cortical actin. Moreover, we observed that protein palmitoylation and PI3K inhibition reduce the sac-like compartment formation rate from 70% to 20% and 40%, respectively.

Conclusions

Our results indicate the involvement of MEND mechanisms during sac-like compartment formation.

The spatial biology of HIV infection

HIV infection implicates a spectrum of tissues in the human body starting with viral transmission in the anogenital tract and subsequently persisting in lymphoid tissues and brain. Though studies using isolated cells have contributed significantly towards our understanding of HIV infection, the tissue microenvironment is characterised by a complex interplay of a range of factors, all of which can influence the course of infection but are otherwise missed in ex vivo studies. To address this knowledge gap, it is necessary to investigate the dynamics of infection and the host immune response in situ using imaging-based approaches. Over the last decade, emerging imaging techniques have continually redefined the limits of detection, both in terms of the scope and the scale of the targets. In doing so, this has opened up new questions that can be answered by in situ studies. This review discusses the high-dimensional imaging modalities that are now available and their application towards understanding the spatial biology of HIV infection.

Deciphering lung granulomas in HIV & TB co-infection: unveiling macrophages aggregation with IL6R/STAT3 activation

Tuberculosis (TB) remains a leading cause of mortality among individuals coinfected with HIV, characterized by progressive pulmonary inflammation. Despite TB's hallmark being focal granulomatous lung lesions, our understanding of the histopathological features and regulation of inflammation in HIV & TB coinfection remains incomplete. In this study, we aimed to elucidate these histopathological features through an immunohistochemistry analysis of HIV & TB co-infected and TB patients, revealing marked differences. Notably, HIV & TB granulomas exhibited aggregation of CD68 + macrophage (Mφ), while TB lesions predominantly featured aggregation of CD20+ B cells, highlighting distinct immune responses in coinfection. Spatial transcriptome profiling further elucidated CD68+ Mφ aggregation in HIV & TB, accompanied by activation of IL6 pathway, potentially exacerbating inflammation. Through multiplex immunostaining, we validated two granuloma types in HIV & TB versus three in TB, distinguished by cell architecture. Remarkably, in the two types of HIV & TB granulomas, CD68 + Mφ highly co-expressed IL6R/pSTAT3, contrasting TB granulomas' high IFNGRA/SOCS3 expression, indicating different signaling pathways at play. Thus, activation of IL6 pathway may intensify inflammation in HIV & TB-lungs, while SOCS3-enriched immune microenvironment suppresses IL6-induced over-inflammation in TB. These findings provide crucial insights into HIV & TB granuloma formation, shedding light on potential therapeutic targets, particularly for granulomatous pulmonary under HIV & TB co-infection. Our study emphasizes the importance of a comprehensive understanding of the immunopathogenesis of HIV & TB coinfection and suggests potential avenues for targeting IL6 signaling with SOCS3 activators or anti-IL6R agents to mitigate lung inflammation in HIV & TB coinfected individuals.

Human genital dendritic cell heterogeneity confers differential rapid response to HIV-1 exposure

Dendritic cells (DCs) play critical roles in HIV pathogenesis and require further investigation in the female genital tract, a main portal of entry for HIV infection. Here we characterized genital DC populations at the single cell level and how DC subsets respond to HIV immediately following exposure. We found that the genital CD11c+HLA-DR+ myeloid population contains three DC subsets (CD1c+ DC2s, CD14+ monocyte-derived DCs and CD14+CD1c+ DC3s) and two monocyte/macrophage populations with distinct functional and phenotypic properties during homeostasis. Following HIV exposure, the antiviral response was dominated by DCs' rapid secretory response, activation of non-classical inflammatory pathways and host restriction factors. Further, we uncovered subset-specific differences in anti-HIV responses. CD14+ DCs were the main population activated by HIV and mediated the secretory antimicrobial response, while CD1c+ DC2s activated inflammasome pathways and IFN responses. Identification of subset-specific responses to HIV immediately after exposure could aid targeted strategies to prevent HIV infection.

Tissue resident cells differentiate S. aureus from S. epidermidis via IL-1β following barrier disruption in healthy human skin

The Staphylococcus sp. are a dominant part of the human skin microbiome and present across the body. Staphylococcus epidermidis is a ubiquitous skin commensal, while S. aureus is thought to colonize at least 30% of the population. S. aureus are not only colonizers but a leading cause of skin and soft tissue infections and a critical healthcare concern. To understand how healthy human skin may differentiate commensal bacteria, such as S. epidermidis, from the potential pathogen methicillin-resistant S. aureus (MRSA), we use ex vivo human skin models that allow us to study this host-bacterial interaction in the most clinically relevant environment. Our work highlights the role of the outer stratum corneum as a protective physical barrier against invasion by colonizing Staphylococci. We show how the structural cells of the skin can internalize and respond to different Staphylococci with increasing sensitivity. In intact human skin, a discriminatory IL-1β response was identified, while disruption of the protective stratum corneum triggered an increased and more diverse immune response. We identified and localized tissue resident Langerhans cells (LCs) as a potential source of IL-1β and go on to show a dose-dependent response of MUTZ-LCs to S. aureus but not S. epidermidis. This suggests an important role of LCs in sensing and discriminating between bacteria in healthy human skin, particularly in intact skin and provides a detailed snapshot of how human skin differentiates between friend and potential foe. With the rise in antibiotic resistance, understanding the innate immune response of healthy skin may help us find ways to enhance or manipulate these natural defenses to prevent invasive infection.

Retinoic acid enhances HIV-1 reverse transcription and transcription in macrophages via mTOR-modulated mechanisms

The intestinal environment facilitates HIV-1 infection via mechanisms involving the gut-homing vitamin A-derived retinoic acid (RA), which transcriptionally reprograms CD4+ T cells for increased HIV-1 replication/outgrowth. Consistently, colon-infiltrating CD4+ T cells carry replication-competent viral reservoirs in people with HIV-1 (PWH) receiving antiretroviral therapy (ART). Intriguingly, integrative infection in colon macrophages, a pool replenished by monocytes, represents a rare event in ART-treated PWH, thus questioning the effect of RA on macrophages. Here, we demonstrate that RA enhances R5 but not X4 HIV-1 replication in monocyte-derived macrophages (MDMs). RNA sequencing, gene set variation analysis, and HIV interactor NCBI database interrogation reveal RA-mediated transcriptional reprogramming associated with metabolic/inflammatory processes and HIV-1 resistance/dependency factors. Functional validations uncover post-entry mechanisms of RA action including SAMHD1-modulated reverse transcription and CDK9/RNA polymerase II (RNAPII)-dependent transcription under the control of mammalian target of rapamycin (mTOR). These results support a model in which macrophages residing in the intestine of ART-untreated PWH contribute to viral replication/dissemination in an mTOR-sensitive manner.

OMIP-103: A 35-marker imaging mass cytometry panel for the co-detection of HIV and immune cell populations in human formalin fixed paraffin embedded intestinal tissue

We introduce a 35-marker imaging mass cytometry (IMC) panel for a detailed examination of immune cell populations and HIV RNA in formalin fixed paraffin embedded (FFPE) human intestinal tissue. The panel has broad cell type coverage and particularly excels in delineating subsets of mononuclear phagocytes and T cells. Markers for key tissue structures are included, enabling identification of epithelium, blood vessels, lymphatics, and musculature. The described method for HIV RNA detection can be generalized to other low abundance RNA targets, whether endogenous or pathogen derived. As such, the panel presented here is useful for high parameter spatial mapping of intestinal immune cells and their interactions with pathogens such as HIV.

Epithelial dendritic cells vs. Langerhans cells: Implications for mucosal vaccines

Next-generation vaccines may be delivered via the skin and mucosa. The stratified squamous epithelium (SSE) represents the outermost layer of the skin (epidermis) and type II mucosa (epithelium). Langerhans cells (LCs) have been considered the sole antigen-presenting cells (APCs) to inhabit the SSE; however, it is now clear that dendritic cells (DCs) are also present. Importantly, there are functional differences in how LCs and DCs take up and process pathogens as well as their ability to activate and polarize T cells, though whether DCs participate in neuroimmune interactions like LCs is yet to be elucidated. A correct definition and functional characterization of APCs in the skin and anogenital tissues are of utmost importance for the design of better vaccines and blocking pathogen transmission. Here, we provide a historical perspective on the evolution of our understanding of the APCs that inhabit the SSE, including a detailed review of the most recent literature.

Nerve-myeloid cell interactions in persistent human pain: a reappraisal using updated cell subset classifications

ABSTRACT

The past 20 years have seen a dramatic shift in our understanding of the role of the immune system in initiating and maintaining pain. Myeloid cells, including macrophages, dendritic cells, Langerhans cells, and mast cells, are increasingly implicated in bidirectional interactions with nerve fibres in rodent pain models. However, our understanding of the human setting is still poor. High-dimensional functional analyses have substantially changed myeloid cell classifications, with recently described subsets such as epidermal dendritic cells and DC3s unveiling new insight into how myeloid cells interact with nerve fibres. However, it is unclear whether this new understanding has informed the study of human chronic pain. In this article, we perform a scoping review investigating neuroimmune interactions between myeloid cells and peripheral nerve fibres in human chronic pain conditions. We found 37 papers from multiple pain states addressing this aim in skin, cornea, peripheral nerve, endometrium, and tumour, with macrophages, Langerhans cells, and mast cells the most investigated. The directionality of results between studies was inconsistent, although the clearest pattern was an increase in macrophage frequency across conditions, phases, and tissues. Myeloid cell definitions were often outdated and lacked correspondence with the stated cell types of interest; overreliance on morphology and traditional structural markers gave limited insight into the functional characteristics of investigated cells. We therefore critically reappraise the existing literature considering contemporary myeloid cell biology and advocate for the application of established and emerging high-dimensional proteomic and transcriptomic single-cell technologies to clarify the role of specific neuroimmune interactions in chronic pain.

Macrophages: Key Cellular Players in HIV Infection and Pathogenesis

Although cells of the myeloid lineages, including tissue macrophages and conventional dendritic cells, were rapidly recognized, in addition to CD4+ T lymphocytes, as target cells of HIV-1, their specific roles in the pathophysiology of infection were initially largely neglected. However, numerous studies performed over the past decade, both in vitro in cell culture systems and in vivo in monkey and humanized mouse animal models, led to growing evidence that macrophages play important direct and indirect roles as HIV-1 target cells and in pathogenesis. It has been recently proposed that macrophages are likely involved in all stages of HIV-1 pathogenesis, including virus transmission and dissemination, but above all, in viral persistence through the establishment, together with latently infected CD4+ T cells, of virus reservoirs in many host tissues, the major obstacle to virus eradication in people living with HIV. Infected macrophages are indeed found, very often as multinucleated giant cells expressing viral antigens, in almost all lymphoid and non-lymphoid tissues of HIV-1-infected patients, where they can probably persist for long period of time. In addition, macrophages also likely participate, directly as HIV-1 targets or indirectly as key regulators of innate immunity and inflammation, in the chronic inflammation and associated clinical disorders observed in people living with HIV, even in patients receiving effective antiretroviral therapy. The main objective of this review is therefore to summarize the recent findings, and also to revisit older data, regarding the critical functions of tissue macrophages in the pathophysiology of HIV-1 infection, both as major HIV-1-infected target cells likely found in almost all tissues, as well as regulators of innate immunity and inflammation during the different stages of HIV-1 pathogenesis.

Single-cell RNA-seq analysis reveals dual sensing of HIV-1 in blood Axl+ dendritic cells

Sensing of incoming viruses is a pivotal task of dendritic cells (DCs). Human primary blood DCs encompass various subsets that are diverse in their susceptibility and response to HIV-1. The recent identification of the blood Axl⁺DC subset, endowed with unique capacities to bind, replicate, and transmit HIV-1 prompted us to evaluate its anti-viral response. We demonstrate that HIV-1 induced two main broad and intense transcriptional programs in different Axl⁺DCs potentially induced by different sensors; an NF-κB-mediated program that led to DC maturation and efficient CD4⁺ T cell activation, and a program mediated by STAT1/2 that activated type I IFN and ISG responses. These responses were absent from cDC2 exposed to HIV-1 except when viral replication was allowed. Finally, Axl⁺DCs actively replicating HIV-1 identified by quantification of viral transcripts exhibited a mixed NF-κB/ISG innate response. Our results suggest that the route of HIV-1 entry may dictate different innate sensing pathways by DCs.

An in situ analysis pipeline for initial host-pathogen interactions reveals signatures of human colorectal HIV transmission

The initial immune response to HIV determines transmission. However, due to technical limitations we still do not have a comparative map of early mucosal transmission events. By combining RNAscope, cyclic immunofluorescence, and image analysis tools, we quantify HIV transmission signatures in intact human colorectal explants within 2 h of topical exposure. We map HIV enrichment to mucosal dendritic cells (DCs) and submucosal macrophages, but not CD4⁺ T cells, the primary targets of downstream infection. HIV⁺ DCs accumulate near and within lymphoid aggregates, which act as early sanctuaries of high viral titers while facilitating HIV passage to the submucosa. Finally, HIV entry induces recruitment and clustering of target cells, facilitating DC- and macrophage-mediated HIV transfer and enhanced infection of CD4⁺ T cells. These data demonstrate a rapid response to HIV structured to maximize the likelihood of mucosal infection and provide a framework for in situ studies of host-pathogen interactions and immune-mediated pathologies.

Langerin-expressing dendritic cells in pulmonary immune-related diseases

Dendritic cells (DCs) are “frontline” immune cells dedicated to antigen presentation. They serve as an important bridge connecting innate and adaptive immunity, and express various receptors for antigen capture. DCs are divided into various subclasses according to their differential expression of cell surface receptors and different subclasses of DCs exhibit specific immunological characteristics. Exploring the common features of each sub-category has became the focus of many studies. There are certain amounts of DCs expressing langerin in airways and peripheral lungs while the precise mechanism by which langerin⁺ DCs drive pulmonary disease is unclear. Langerin-expressing DCs can be further subdivided into numerous subtypes based on the co-expressed receptors, but here, we identify commonalities across these subtypes that point to the major role of langerin. Better understanding is required to clarify key disease pathways and determine potential new therapeutic approaches.