Monocyte heterogeneity underlying phenotypic changes in monocytes according to SIV disease stage

Simian immunodeficiency virus-infected rhesus macaques with AIDS co-develop cardiovascular pathology and encephalitis

Despite effective antiretroviral therapy, HIV co-morbidities remain where central nervous system (CNS) neurocognitive disorders and cardiovascular disease (CVD)-pathology that are linked with myeloid activation are most prevalent. Comorbidities such as neurocogntive dysfunction and cardiovascular disease (CVD) remain prevalent among people living with HIV. We sought to investigate if cardiac pathology (inflammation, fibrosis, cardiomyocyte damage) and CNS pathology (encephalitis) develop together during simian immunodeficiency virus (SIV) infection and if their co-development is linked with monocyte/macrophage activation. We used a cohort of SIV-infected rhesus macaques with rapid AIDS and demonstrated that SIV encephalitis (SIVE) and CVD pathology occur together more frequently than SIVE or CVD pathology alone. Their co-development correlated more strongly with activated myeloid cells, increased numbers of CD14+CD16+ monocytes, plasma CD163 and interleukin-18 (IL-18) than did SIVE or CVD pathology alone, or no pathology. Animals with both SIVE and CVD pathology had greater numbers of cardiac macrophages and increased collagen and monocyte/macrophage accumulation, which were better correlates of CVD-pathology than SIV-RNA. Animals with SIVE alone had higher levels of activated macrophage biomarkers and cardiac macrophage accumulation than SIVnoE animals. These observations were confirmed in HIV infected individuals with HIV encephalitis (HIVE) that had greater numbers of cardiac macrophages and fibrosis than HIV-infected controls without HIVE. These results underscore the notion that CNS and CVD pathologies frequently occur together in HIV and SIV infection, and demonstrate an unmet need for adjunctive therapies targeting macrophages.

Viral dissemination and immune activation modulate antiretroviral drug levels in lymph nodes of SIV-infected rhesus macaques

Introduction and methods

To understand the relationship between immunovirological factors and antiretroviral (ARV) drug levels in lymph nodes (LN) in HIV therapy, we analyzed drug levels in twenty-one SIV-infected rhesus macaques subcutaneously treated with daily tenofovir (TFV) and emtricitabine (FTC) for three months.

Results

The intracellular active drug-metabolite (IADM) levels (TFV-dp and FTC-tp) in lymph node mononuclear cells (LNMC) were significantly lower than in peripheral blood mononuclear cells (PBMC) (P≤0.005). Between Month 1 and Month 3, IADM levels increased in both LNMC (P≤0.001) and PBMC (P≤0.01), with a steeper increase in LNMC (P≤0.01). The viral dissemination in plasma, LN, and rectal tissue at ART initiation correlated negatively with IADM levels at Month 1. Physiologically-based pharmacokinetic model simulations suggest that, following subcutaneous ARV administration, ART-induced reduction of immune activation improves the formation of active drug-metabolites through modulation of kinase activity and/or through improved parent drug accessibility to LN cellular compartments.

Conclusion

These observations have broad implications for drugs that need to phosphorylate to exert their pharmacological activity, especially in the settings of the pre-/post-exposure prophylaxis and efficacy of antiviral therapies targeting pathogenic viruses such as HIV or SARS-CoV-2 replicating in highly inflammatory anatomic compartments.

Differential expression of chemokine receptors on monocytes in TB and HIV

In the present study, we defined multiple chemokine receptors expressed by classical, intermediate and non-classical monocyte subsets in TB, HIV and TB/HIV co-infection and associate it with the perturbation of monocyte subsets due to the diseases. Peripheral blood mononuclear cells from TB+ (n = 34), HIV+ (n = 35), TB + HIV+ (n = 12), as well as TB-HIV- healthy controls (n = 39), were tested for monocyte phenotyping by flow cytometry. Frequencies of intermediate and non-classical monocytes were significantly higher in TB and/or HIV disease relative to healthy controls. CCR2 and CX3CR1 were significantly higher on monocytes in TB disease, whereas CCR4 and CCR5 were present at higher levels in HIV disease. TB/HIV co-infected patients exhibited CCR2, CCR5 and CX3CR1 levels intermediate to TB and HIV subjects, while CCR4 was at a higher level than HIV. Despite the increase in the expression of chemokine receptors due to disease conditions, chemokine receptors maintained their original expression pattern on monocyte subsets. Our data provided new insight into the disease-specific but not monocyte subsets-specific modulation of chemokine receptors in TB and HIV.

Monocyte subpopulations display disease-specific miRNA signatures depending on the subform of Spondyloarthropathy

Spondyloarthropathies (SpA) are a family of rheumatic disorders that could be divided into axial (axSpA) and peripheral (perSpA) sub-forms depending on the disease clinical presentation. The chronic inflammation is believed to be driven by innate immune cells such as monocytes, rather than self-reactive cells of adaptive immune system. The aim of the study was to investigate the micro-RNA (miRNA) profiles in monocyte subpopulations (classical, intermediate and non-classical subpopulations) acquired from SpA patients or healthy individuals in search for prospective disease specific and/or disease subtype differentiating miRNA markers. Several SpA-specific and axSpA/perSpA differentiating miRNAs have been identified that appear to be characteristic for specific monocyte subpopulation. For classical monocytes, upregulation of miR-567 and miR-943 was found to be SpA-specific, whereas downregulation of miR-1262 could serve as axSpA-differentiating, and the expression pattern of miR-23a, miR-34c, mi-591 and miR-630 as perSpA-differentiating markers. For intermediate monocytes, expression levels of miR-103, miR-125b, miR-140, miR-374, miR-376c and miR-1249 could be used to distinguish SpA patients from healthy donors, whereas the expression pattern of miR-155 was identified as characteristic for perSpA. For non-classical monocytes, differential expression of miR-195 was recognized as general SpA indicator, while upregulation of miR-454 and miR-487b could serve as axSpA-differentiating, and miR-1291 as perSpA-differentiating markers. Our data indicate for the first time that in different SpA subtypes, monocyte subpopulations bear disease-specific miRNA signatures that could be relevant for SpA diagnosis/differentiation process and may help to understand SpA etiopathology in the context of already known functions of monocyte subpopulations.

Effect of Single Housing on Innate Immune Activation in Immunodeficiency Virus-Infected Pigtail Macaques ( Macaca nemestrina ) as a Model of Psychosocial Stress in Acute HIV Infection

OBJECTIVE

Simian immunodeficiency virus (SIV) infection of macaques recapitulates many aspects of HIV pathogenesis and is similarly affected by both genetic and environmental factors. Psychosocial stress is associated with immune system dysregulation and worse clinical outcomes in people with HIV. This study assessed the impact of single housing, as a model of psychosocial stress, on innate immune responses of pigtailed macaques ( Macaca nemestrina ) during acute SIV infection.

METHODS

A retrospective analysis of acute SIV infection of 2- to si6-year-old male pigtailed macaques was performed to compare the innate immune responses of socially ( n = 41) and singly ( n = 35) housed animals. Measures included absolute monocyte count and subsets, and in a subset ( n ≤ 18) platelet counts and activation data.

RESULTS

SIV infection resulted in the expected innate immune parameter changes with a modulating effect from housing condition. Monocyte number increased after infection for both groups, driven by classical monocytes (CD14 + CD16 - ), with a greater increase in socially housed animals (227%, p < .001, by day 14 compared with preinoculation time points). Platelet numbers recovered more quickly in the socially housed animals. Platelet activation (P-selectin) increased by 65% ( p = .004) and major histocompatibility complex class I surface expression by 40% ( p = .009) from preinoculation only in socially housed animals, whereas no change in these measures occurred in singly housed animals.

CONCLUSIONS

Chronic psychosocial stress produced by single housing may play an immunomodulatory role in the innate immune response to acute retroviral infection. Dysregulated innate immunity could be one of the pathways by which psychosocial stress contributes to immune suppression and increased disease severity in people with HIV.

Phenotypic and Kinetic Changes of Myeloid Lineage Cells in Innate Response to Chikungunya Infection in Cynomolgus Macaques

Chikungunya (CHIKV) is an emerging worldwide viral threat. The immune response to infection can lead to protection and convalescence or result in long-term sequelae such as arthritis. Early innate immune events during acute infection have been characterized for some cell types, but more must be elucidated with respect to cellular responses of monocytes and other myeloid lineage cells. In addition to their roles in protection and inflammation resolution, monocytes and macrophages are sites for viral replication and may also act as viral reservoirs. These cells are also found in joints postinfection, possibly playing a role in long-term CHIKV-induced pathology. We examined kinetic and phenotypic changes in myeloid lineage cells, including monocytes, in cynomolgus macaques early after experimental infection with CHIKV. We found increased proliferation of monocytes and decreased proliferation of myeloid dendritic cells early during infection, with an accompanying decrease in absolute numbers of both cell types, as well as a simultaneous increase in plasmacytoid dendritic cell number. An increase in CD16 and CD14 was seen along with a decrease in monocyte Human Leukocyte Antigen-DR isotype expression within 3 days of infection, potentially indicating monocyte deactivation. A transient decrease in T cells, B cells, and natural killer cells correlated with lymphocytopenia observed during human infections with CHIKV. CD4⁺ T cell proliferation decreased in blood, indicating relocation of cells to effector sites. These data indicate CHIKV influences proliferation rates and kinetics of myeloid lineage cells early during infection and may prove useful in development of therapeutics and evaluation of infection-induced pathogenesis.

Monocytes in HIV and SIV Infection and Aging: Implications for Inflamm-Aging and Accelerated Aging

Before the antiretroviral therapy (ART) era, people living with HIV (PLWH) experienced complications due to AIDS more so than aging. With ART and the extended lifespan of PLWH, HIV comorbidities also include aging—most likely due to accelerated aging—as well as a cardiovascular, neurocognitive disorders, lung and kidney disease, and malignancies. The broad evidence suggests that HIV with ART is associated with accentuated aging, and that the age-related comorbidities occur earlier, due in part to chronic immune activation, co-infections, and possibly the effects of ART alone. Normally the immune system undergoes alterations of lymphocyte and monocyte populations with aging, that include diminished naïve T- and B-lymphocyte numbers, a reliance on memory lymphocytes, and a skewed production of myeloid cells leading to age-related inflammation, termed “inflamm-aging”. Specifically, absolute numbers and relative proportions of monocytes and monocyte subpopulations are skewed with age along with myeloid mitochondrial dysfunction, resulting in increased accumulation of reactive oxygen species (ROS). Additionally, an increase in biomarkers of myeloid activation (IL-6, sCD14, and sCD163) occurs with chronic HIV infection and with age, and may contribute to immunosenescence. Chronic HIV infection accelerates aging; meanwhile, ART treatment may slow age-related acceleration, but is not sufficient to stop aging or age-related comorbidities. Overall, a better understanding of the mechanisms behind accentuated aging with HIV and the effects of myeloid activation and turnover is needed for future therapies.

So Pathogenic or So What?-A Brief Overview of SIV Pathogenesis with an Emphasis on Cure Research

HIV infection requires lifelong antiretroviral therapy (ART) to control disease progression. Although ART has greatly extended the life expectancy of persons living with HIV (PWH), PWH nonetheless suffer from an increase in AIDS-related and non-AIDS related comorbidities resulting from HIV pathogenesis. Thus, an HIV cure is imperative to improve the quality of life of PWH. In this review, we discuss the origins of various SIV strains utilized in cure and comorbidity research as well as their respective animal species used. We briefly detail the life cycle of HIV and describe the pathogenesis of HIV/SIV and the integral role of chronic immune activation and inflammation on disease progression and comorbidities, with comparisons between pathogenic infections and nonpathogenic infections that occur in natural hosts of SIVs. We further discuss the various HIV cure strategies being explored with an emphasis on immunological therapies and "shock and kill".

Cerebrospinal fluid CD4+ T cell infection in humans and macaques during acute HIV-1 and SHIV infection

HIV-1 replication within the central nervous system (CNS) impairs neurocognitive function and has the potential to establish persistent, compartmentalized viral reservoirs. The origins of HIV-1 detected in the CNS compartment are unknown, including whether cells within the cerebrospinal fluid (CSF) produce virus. We measured viral RNA+ cells in CSF from acutely infected macaques longitudinally and people living with early stages of acute HIV-1. Active viral transcription (spliced viral RNA) was present in CSF CD4+ T cells as early as four weeks post-SHIV infection, and among all acute HIV-1 specimens (N = 6; Fiebig III/IV). Replication-inactive CD4+ T cell infection, indicated by unspliced viral RNA in the absence of spliced viral RNA, was even more prevalent, present in CSF of >50% macaques and human CSF at ~10-fold higher frequency than productive infection. Infection levels were similar between CSF and peripheral blood (and lymph nodes in macaques), indicating comparable T cell infection across these compartments. In addition, surface markers of activation were increased on CSF T cells and monocytes and correlated with CSF soluble markers of inflammation. These studies provide direct evidence of HIV-1 replication in CD4+ T cells and broad immune activation in peripheral blood and the CNS during acute infection, likely contributing to early neuroinflammation and reservoir seeding. Thus, early initiation of antiretroviral therapy may not be able to prevent establishment of CNS viral reservoirs and sources of long-term inflammation, important targets for HIV-1 cure and therapeutic strategies.

Neurological pathologies are associated with HIV-1 infection and remain common in the ongoing AIDS epidemic. Despite the advent of successful viremia suppression by anti-retroviral therapy, increased life expectancies and co-morbidities have led to higher prevalence of milder forms of neurocognitive dysfunction. How HIV-1 causes neurocognitive dysfunction is currently unclear, though it is widely believed that viral replication within the central nervous system (CNS) prior to therapy triggers these detrimental processes. The appearance of HIV-1 in the cerebrospinal fluid during the earliest stages of infection suggests that these processes may begin very early. Here, we use novel techniques to probe cells for viral infection during the first few weeks of infection in the CNS of humans and animals to determine the source of this virus. We found HIV-1 replication in T cells in the cerebrospinal fluid during this early window. In addition, infected T cells were present at similar frequencies in the CNS and other anatomic compartments, suggesting equilibration of T cell infection levels across these sites and potential for establishment of long-term reservoirs in the CNS. Our study provides new insights to the early events of viral entry and replication in the CNS with implications for subsequent viral persistence and neuronal injury.

Predator-Prey Dynamics of Intra-Host Simian Immunodeficiency Virus Evolution Within the Untreated Host

The dynamic nature of the SIV population during disease progression in the SIV/macaque model of AIDS and the factors responsible for its behavior have not been documented, largely owing to the lack of sufficient spatial and temporal sampling of both viral and host data from SIV-infected animals. In this study, we detail Bayesian coalescent inference of the changing collective intra-host viral effective population size (N_e ) from various tissues over the course of infection and its relationship with what we demonstrate is a continuously changing immune cell repertoire within the blood. Although the relative contribution of these factors varied among hosts and time points, the adaptive immune response best explained the overall periodic dynamic behavior of the effective virus population. Data exposing the nature of the relationship between the virus and immune cell populations revealed the plausibility of an eco-evolutionary mathematical model, which was able to mimic the large-scale oscillations in N_e through virus escape from relatively few, early immunodominant responses, followed by slower escape from several subdominant and weakened immune populations. The results of this study suggest that SIV diversity within the untreated host is governed by a predator-prey relationship, wherein differing phases of infection are the result of adaptation in response to varying immune responses. Previous investigations into viral population dynamics using sequence data have focused on single estimates of the effective viral population size (N_e ) or point estimates over sparse sampling data to provide insight into the precise impact of immune selection on virus adaptive behavior. Herein, we describe the use of the coalescent phylogenetic frame- work to estimate the relative changes in N_e over time in order to quantify the relationship with empirical data on the dynamic immune composition of the host. This relationship has allowed us to expand on earlier simulations to build a predator-prey model that explains the deterministic behavior of the virus over the course of disease progression. We show that sequential viral adaptation can occur in response to phases of varying immune pressure, providing a broader picture of the viral response throughout the entire course of progression to AIDS.

Systemic and mucosal mobilization of granulocyte subsets during lentiviral infection

Granulocytes mediate broad immunoprotection through phagocytosis, extracellular traps, release of cytotoxic granules, antibody effector functions and recruitment of other immune cells against pathogens. However, descriptions of granulocytes in HIV infection and mucosal tissues are limited. Our goal was to characterize granulocyte subsets in systemic, mucosal and lymphoid tissues during lentiviral infection using the rhesus macaque (RM) model. Mononuclear cells from jejunum, colon, cervix, vagina, lymph nodes, spleen, liver and whole blood from experimentally naïve and chronically SHIVsf162p3-infected RM were analysed by microscopy and polychromatic flow cytometry. Granulocytes were identified using phenotypes designed specifically for RM: eosinophils-CD45+  CD66+  CD49d+ ; neutrophils-CD45+  CD66+  CD14+ ; and basophils-CD45+  CD123+  FcRε+ . Nuclear visualization with DAPI staining and surface marker images by ImageStream (cytometry/microscopy) further confirmed granulocytic phenotypes. Flow cytometric data showed that all RM granulocytes expressed CD32 (FcRγII) but did not express CD16 (FcRγIII). Additionally, constitutive expression of CD64 (FcRγI) on neutrophils and FcRε on basophils indicates the differential expression of Fc receptors on granulocyte subsets. Granulocytic subsets in naïve whole blood ranged from 25·4% to 81·5% neutrophils, 0·59% to 13·3% eosinophils and 0·059% to 1·8% basophils. Interestingly, elevated frequencies of circulating neutrophils, colorectal neutrophils and colorectal eosinophils were all observed in chronic lentiviral disease. Conversely, circulating basophils, jejunal eosinophils, vaginal neutrophils and vaginal eosinophils of SHIVsf162p3-infected RM declined in frequency. Overall, our data suggest modulation of granulocytes in chronic lentiviral infection, most notably in the gastrointestinal mucosae where a significant inflammation and disruption occurs in lentivirus-induced disease. Furthermore, granulocytes may migrate to inflamed tissues during infection and could serve as targets of immunotherapeutic intervention.

HIV-1 Nef Induces Hck/Lyn-Dependent Expansion of Myeloid-Derived Suppressor Cells Associated with Elevated Interleukin-17/G-CSF Levels

Human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) infection causes myelodysplasia, anemia, and accumulation of inflammatory monocytes (CD14⁺ CD16⁺) through largely unknown cellular and molecular pathways. The mouse cells thought to be equivalent to human CD14⁺ CD16⁺ cells are CD11b⁺ Gr1⁺ myeloid-derived suppressor cells (MDSC). We used HIV transgenic (Tg) mouse models to study MDSC, namely, CD4C/Nef Tg mice expressing nef in dendritic cells (DC), pDC, CD4⁺ T, and other mature and immature myeloid cells and CD11c/Nef Tg mice with a more restricted expression, mainly in DC and pDC. Both Tg strains showed expansion of granulocytic and CD11b⁺ Gr1^low/int cells with MDSC characteristics. Fetal liver cell transplantation revealed that this expansion was stroma-independent and abrogated in mixed Tg/non-Tg 50% chimera. Tg bone marrow (BM) erythroid progenitors were decreased and myeloid precursors increased, suggesting an aberrant differentiation likely driving CD11b⁺ Gr1⁺ cell expansion, apparently cell autonomously in CD4C/Nef Tg mice and likely through a bystander effect in CD11c/Nef Tg mice. Hck was activated in Tg spleen, and Nef-mediated CD11b⁺ Gr1⁺ cell expansion was abrogated in Hck/Lyn-deficient Nef Tg mice, indicating a requirement of Hck/Lyn for this Nef function. IL-17 and granulocyte colony-stimulating factor (G-CSF) were elevated in Nef Tg mice. Increased G-CSF levels were normalized in Tg mice treated with anti-IL-17 antibodies. Therefore, Nef expression in myeloid precursors causes severe BM failure, apparently cell autonomously. More cell-restricted expression of Nef in DC and pDC appears sufficient to induce BM differentiation impairment, granulopoiesis, and expansion of MDSC at the expense of erythroid maturation, with IL-17→G-CSF as one likely bystander contributor. IMPORTANCE HIV-1 and SIV infection often lead to myelodysplasia, anemia, and accumulation of inflammatory monocytes (CD14⁺ CD16⁺), with the latter likely involved in neuroAIDS. We found that some transgenic (Tg) mouse models of AIDS also develop accumulation of mature and immature cells of the granulocytic lineage, decreased erythroid precursors, and expansion of MDSC (equivalent to human CD14⁺ CD16⁺ cells). We identified Nef as being responsible for these phenotypes, and its expression in mouse DC appears sufficient for their development through a bystander mechanism. Nef expression in myeloid progenitors may also favor myeloid cell expansion, likely in a cell-autonomous way. Hck/Lyn is required for the Nef-mediated accumulation of myeloid cells. Finally, we identified G-CSF under the control of IL-17 as one bystander mediator of MDSC expansion. Our findings provide a framework to determine whether the Nef>Hck/Lyn>IL-17>G-CSF pathway is involved in human AIDS and whether it represents a valid therapeutic target.

Innate Immune Response Against HIV-1

The innate immune system is comprised of both cellular and humoral players that recognise and eradicate invading pathogens. Therefore, the interplay between retroviruses and innate immunity has emerged as an important component of viral pathogenesis. HIV-1 infection in humans that results in hematologic abnormalities and immune suppression is well represented by changes in the CD4/CD8 T cell ratio and consequent cell death causing CD4 lymphopenia. The innate immune responses by mucosal barriers such as complement, DCs, macrophages, and NK cells as well as cytokine/chemokine profiles attain great importance in acute HIV-1 infection, and thus, prevent mucosal capture and transmission of HIV-1. Conversely, HIV-1 has evolved to overcome innate immune responses through RNA-mediated rapid mutations, pathogen-associated molecular patterns (PAMPs) modification, down-regulation of NK cell activity and complement receptors, resulting in increased secretion of inflammatory factors. Consequently, epithelial tissues lining up female reproductive tract express innate immune sensors including anti-microbial peptides responsible for forming primary barriers and have displayed an effective potent anti-HIV activity during phase I/II clinical trials.

Plasticity of monocyte development and monocyte fates

Monocytes are circulating myeloid immune precursor cells that are generated in the bone marrow. Mature monocytes are released into the circulation and, in case of need, recruited to peripheral sites of inflammation to differentiate into monocyte-derived effector cells. In absence of overt inflammation, monocytes also extravasate into selected tissues, where they complement tissue-resident macrophage compartments. Adjustment of these homeostatic monocyte infiltrates to local environment is critical to maintain health, as best established for the intestine. Defined gene expression changes that differ between gut segments presumably help strike the fine balance between the crucial function of these monocyte-derived macrophages as tissue rheostats and their detrimental hyperactivation. Environmental factors that dictate local monocyte differentiation remain incompletely understood. Definition of the latter could aid our general understanding of in vivo monocyte functions and their relation to inflammatory disorders. In this review, we summarize recent advances in our understanding of monocyte subsets, their differentiation into tissue macrophages, and selected contributions of monocyte-derived cells to steady-state physiology. Moreover, we will discuss emerging evidence for an intriguing bifurcation of monocyte development in the bone marrow and potential functional implications. Emphasis will be given to points of controversies, but we will largely focus on the healthy organism. For a discussion of monocyte and macrophage contributions to inflammatory conditions, we refer the reader to other dedicated reviews.

Early Antiretroviral Therapy Prevents Viral Infection of Monocytes and Inflammation in Simian Immunodeficiency Virus-Infected Rhesus Macaques

Despite early antiretroviral therapy (ART), treatment interruption is associated with viral rebound, indicating early viral reservoir (VR) seeding and absence of full eradication of human immunodeficiency virus type 1 (HIV-1) that may persist in tissues. Herein, we address the contributing role of monocytes in maintaining VRs under ART, since these cells may represent a source of viral dissemination due to their ability to replenish mucosal tissues in response to injury. To this aim, monocytes with classical (CD14⁺), intermediate (CD14⁺ CD16⁺), and nonclassical (CD16⁺) phenotypes and CD4⁺ T cells were sorted from the blood, spleen, and intestines of untreated and early-ART-treated simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) before and after ART interruption. Cell-associated SIV DNA and RNA were quantified. We demonstrated that in the absence of ART, monocytes were productively infected with replication-competent SIV, especially in the spleen. Reciprocally, early ART efficiently (i) prevented the establishment of monocyte VRs in the blood, spleen, and intestines and (ii) reduced systemic inflammation, as indicated by changes in interleukin-18 (IL-18) and IL-1 receptor antagonist (IL-1Ra) plasma levels. ART interruption was associated with a rebound in viremia that led to the rapid productive infection of both CD4⁺ T cells and monocytes. Altogether, our results reveal the benefits of early ART initiation in limiting the contribution of monocytes to VRs and SIV-associated inflammation.IMPORTANCE Despite the administration of antiretroviral therapy (ART), HIV persists in treated individuals and ART interruption is associated with viral rebound. Persistent chronic immune activation and inflammation contribute to disease morbidity. Whereas monocytes are infected by HIV/SIV, their role as viral reservoirs (VRs) in visceral tissues has been poorly explored. Our work demonstrates that monocyte cell subsets in the blood, spleen, and intestines do not significantly contribute to the establishment of early VRs in SIV-infected rhesus macaques treated with ART. By preventing the infection of these cells, early ART reduces systemic inflammation. However, following ART interruption, monocytes are rapidly reinfected. Altogether, our findings shed new light on the benefits of early ART initiation in limiting VR and inflammation.

Pattern of human monocyte subpopulations in health and disease

Monocytes are important cells of the innate system. They are a heterogeneous type of cells consisting of phenotypically and functionally distinct subpopulations, which play a specific role in the control, development and escalation of the immunological processes. Based on the expression of superficial CD14 and CD16 in flow cytometry, they can be divided into three subsets: classical, intermediate and non-classical. Variation in the levels of human monocyte subsets in the blood can be observed in patients in numerous pathological states, such as infections, cardiovascular and inflammatory diseases, cancer and autoimmune diseases. The aim of this review is to summarize current knowledge of human monocyte subsets and their significance in homeostasis and in pathological conditions.

Phenotype of Innate Immune Cells in Uveitis Associated with Axial Spondyloarthritis- and Juvenile Idiopathic Arthritis-associated Uveitis

Purpose: To analyze circulating immune cells in patients with anterior uveitis (AU) associated to axial spondyloarthritis (SpA), or juvenile idiopathic arthritis (JIA).Methods: Venous blood samples were collected from healthy controls (n = 16), and either SpA (n = 19) or JIA (n = 23) patients with associated anterior uveitis (AU) during active flare, or after ≥3 months of inactivity. Frequencies of CD56⁺, MHC-I⁺, and S100A9⁺ monocytes, CCR7⁺ dendritic cells, CD56^+dim natural killer (NK) cells and CD3⁺CD56^bright T-cells were analyzed via flow cytometry. Serum S100A8/A9 levels were determined via ELISA.Results: SpA patients showed a reduced frequency of CD56^+dim NK cells during uveitis activity, a constitutively activated monocyte phenotype, and elevated S100A8/A9 serum levels. In contrast, JIAU patients showed elevated frequencies of CD56⁺ monocytes and CCR7⁺ DC.Conclusion: Phenotype of peripheral immune cells differ between patients, probably contributing to different courses of acute onset AU in SpA and insidious onset AU in JIAU patients.Abbreviations: AU: anterior uveitis, AR: arthritis, JIA: juvenile idiopathic arthritis, SpA: axial spondyloarthritis.

Nonhuman Primate Models of Immunosenescence

Due to a dramatic increase in life expectancy, the number of individuals aged 65 and older is rapidly rising. This presents considerable challenges to our health care system since advanced age is associated with a higher susceptibility to infectious diseases due to immune senescence. However, the mechanisms underlying age-associated dysregulated immunity are still incompletely understood. Advancement in our comprehension of mechanisms of immune senescence and development of interventions to improve health span requires animal models that closely recapitulate the physiological changes that occur with aging in humans. Nonhuman primates (NHPs) are invaluable preclinical models to study the underlying causal mechanism of pathogenesis due to their outbred nature, high degree of genetic and physiological similarity to humans, and their susceptibility to human pathogens. In this chapter, we review NHP models available for biogerontology research, advantages and challenges they present, and advances they facilitated. Furthermore, we emphasize the utility of NHPs in characterizing immune senescence, evaluating interventions to reverse aging of the immune system, and development of vaccine strategies that are better suited for this vulnerable population.

Functional alterations of myeloid cells during the course of Alzheimer's disease

BACKGROUND

Neuroinflammation is a hallmark of neurodegenerative disease and a significant component of the pathology of Alzheimer's disease (AD). Patients present with extensive microgliosis along with elevated pro-inflammatory signaling in the central nervous system and periphery. However, the role of peripheral myeloid cells in mediating and influencing AD pathogenesis remains unresolved.

METHODS

Peripheral myeloid cells were isolated from peripheral blood of patients with prodromal AD (n = 44), mild AD dementia (n = 25), moderate/severe AD dementia (n = 28), and age-matched controls (n = 54). Patients were evaluated in the clinic for AD severity and categorized using Clinical Dementia Rating (CDR) scale resulting in separation of patients into prodromal AD (CDR0.5) and advancing forms of AD dementia (mild-CDR1 and moderate/severe-CDR2/3). Separation of peripheral myeloid cells into mature monocytes or immature MDSCs permitted the delineation of population changes from flow cytometric analysis, RNA phenotype analysis, and functional studies using T cell suppression assays and monocyte suppression assays.

RESULTS

During stages of AD dementia (CDR1 and 2/3) peripheral myeloid cells increase their pro-inflammatory gene expression while at early stages of disease (prodromal AD-CDR0.5) pro-inflammatory gene expression is decreased. MDSCs are increased in prodromal AD compared with controls (16.81% vs 9.53%) and have markedly increased suppressive functions: 42.4% suppression of activated monocyte-produced IL-6 and 78.16% suppression of T cell proliferation. In AD dementia, MDSC populations are reduced with decreased suppression of monocyte IL-6 (5.22%) and T cell proliferation (37.61%); the reduced suppression coincides with increased pro-inflammatory signaling in AD dementia monocytes.

CONCLUSIONS

Peripheral monocyte gene expression is pro-inflammatory throughout the course of AD, except at the earliest, prodromal stages when pro-inflammatory gene expression is suppressed. This monocyte biphasic response is associated with increased numbers and suppressive functions of MDSCs during the early stages and decreased numbers and suppressive functions in later stages of disease. Prolonging the early protective suppression and reversing the later loss of suppressive activity may offer a novel therapeutic strategy.

Effects of HIV infection and ART on phenotype and function of circulating monocytes, natural killer, and innate lymphoid cells

HIV infection causes upregulation of markers of inflammation, immune activation and apoptosis of host adaptive, and innate immune cells particularly monocytes, natural killer (NK) and innate lymphoid cells (ILCs). Although antiretroviral therapy (ART) restores CD4 T-cell counts, the persistent aberrant activation of monocytes, NK and ILCs observed likely contributes to the incomplete recovery of T-cell effector functions. A better understanding of the effects of HIV infection and ART on the phenotype and function of circulating monocytes, NK, and ILCs is required to guide development of novel therapeutic interventions to optimize immune recovery.

An SIV macaque model of SIV and HAND: the need for adjunctive therapies in HIV that target activated monocytes and macrophages

Non-human primate models of AIDS and neuroAIDS are critical to study HIV infection of the CNS, neuropathology, and immune activation and macrophage accumulation that occurs in HAND. SIV, similar to HIV, infects CD4⁺ T lymphocytes and monocytes/macrophages. Virus enters the CNS early, and macrophage activation correlates with CNS disease, as well as inflammation outside of the CNS. Antiretroviral in HIV+ humans and SIV+ Rhesus macaques results in non-detectable plasma virus, decreased or non-detectable viral RNA or protein in the CNS. But, viral DNA rebounds following therapy interruption, demonstrating the presence of replication competent virus in the CNS within myeloid cells. In this brief review, we discuss our findings using a Rhesus macaque model of SIV-associated CNS infection and pathology, focusing on monocyte/macrophage activation and the link between CNS and cardiac disease. We conclude with recent studies using adjunctive therapy targeting monocytes/macrophages with ART to prevent or diminish CNS pathology that may be associated with HAND.

The Biology of Monocytes and Dendritic Cells: Contribution to HIV Pathogenesis

Myeloid cells such as monocytes, dendritic cells (DC) and macrophages (MΦ) are key components of the innate immune system contributing to the maintenance of tissue homeostasis and the development/resolution of immune responses to pathogens. Monocytes and DC, circulating in the blood or infiltrating various lymphoid and non-lymphoid tissues, are derived from distinct bone marrow precursors and are typically short lived. Conversely, recent studies revealed that subsets of tissue resident MΦ are long-lived as they originate from embryonic/fetal precursors that have the ability to self-renew during the life of an individual. Pathogens such as the human immunodeficiency virus type 1 (HIV-1) highjack the functions of myeloid cells for viral replication (e.g., MΦ) or distal dissemination and cell-to-cell transmission (e.g., DC). Although the long-term persistence of HIV reservoirs in CD4+ T-cells during viral suppressive antiretroviral therapy (ART) is well documented, the ability of myeloid cells to harbor replication competent viral reservoirs is still a matter of debate. This review summarizes the current knowledge on the biology of monocytes and DC during homeostasis and in the context of HIV-1 infection and highlights the importance of future studies on long-lived resident MΦ to HIV persistence in ART-treated patients.

Liver macrophage-associated inflammation correlates with SIV burden and is substantially reduced following cART

Liver disease is a leading contributor to morbidity and mortality during HIV infection, despite the use of combination antiretroviral therapy (cART). The precise mechanisms of liver disease during HIV infection are poorly understood partially due to the difficulty in obtaining human liver samples as well as the presence of confounding factors (e.g. hepatitis co-infection, alcohol use). Utilizing the simian immunodeficiency virus (SIV) macaque model, a controlled study was conducted to evaluate the factors associated with liver inflammation and the impact of cART. We observed an increase in hepatic macrophages during untreated SIV infection that was associated with a number of inflammatory and fibrosis mediators (TNFα, CCL3, TGFβ). Moreover, an upregulation in the macrophage chemoattractant factor CCL2 was detected in the livers of SIV-infected macaques that coincided with an increase in the number of activated CD16+ monocyte/macrophages and T cells expressing the cognate receptor CCR2. Expression of Mac387 on monocyte/macrophages further indicated that these cells recently migrated to the liver. The hepatic macrophage and T cell levels strongly correlated with liver SIV DNA levels, and were not associated with the levels of 16S bacterial DNA. Utilizing in situ hybridization, SIV-infected cells were found primarily within portal triads, and were identified as T cells. Microarray analysis identified a strong antiviral transcriptomic signature in the liver during SIV infection. In contrast, macaques treated with cART exhibited lower levels of liver macrophages and had a substantial, but not complete, reduction in their inflammatory profile. In addition, residual SIV DNA and bacteria 16S DNA were detected in the livers during cART, implicating the liver as a site on-going immune activation during antiretroviral therapy. These findings provide mechanistic insights regarding how SIV infection promotes liver inflammation through macrophage recruitment, with implications for in HIV-infected individuals.

Aged Chinese-origin rhesus macaques infected with SIV develop marked viremia in absence of clinical disease, inflammation or cognitive impairment

Background

Damage to the central nervous system during HIV infection can lead to variable neurobehavioral dysfunction termed HIV-associated neurocognitive disorders (HAND). There is no clear consensus regarding the neuropathological or cellular basis of HAND. We sought to study the potential contribution of aging to the pathogenesis of HAND. Aged (range = 14.7–24.8 year) rhesus macaques of Chinese origin (RM-Ch) (n = 23) were trained to perform cognitive tasks. Macaques were then divided into four groups to assess the impact of SIVmac251 infection (n = 12) and combined antiretroviral therapy (CART) (5 infected; 5 mock-infected) on the execution of these tasks.

Results

Aged SIV-infected RM-Ch demonstrated significant plasma viremia and modest CSF viral loads but showed few clinical signs, no elevations of systemic temperature, and no changes in activity levels, platelet counts or weight. Concentrations of biomarkers of acute and chronic inflammation such as soluble CD14, CXCL10, IL-6 and TNF-α are known to be elevated following SIV infection of young adult macaques of several species, but concentrations of these biomarkers did not shift after SIV infection in aged RM-Ch and remained similar to mock-infected macaques. Neither acute nor chronic SIV infection or CART had a significant impact on accuracy, speed or percent completion in a sensorimotor test.

Conclusions

Viremia in the absence of a chronic elevated inflammatory response seen in some aged RM-Ch is reminiscent of SIV infection in natural disease resistant hosts. The absence of cognitive impairment during SIV infection in aged RM-Ch might be in part attributed to diminishment of some facets of the immunological response. Additional study encompassing species and age differences is necessary to substantiate this hypothesis.

Electronic supplementary material

The online version of this article (10.1186/s12977-018-0400-y) contains supplementary material, which is available to authorized users.

Monocyte subsets exhibit transcriptional plasticity and a shared response to interferon in SIV-infected rhesus macaques

The progression to AIDS is influenced by changes in the biology of heterogeneous monocyte subsets. Classical (CD14++CD16-), intermediate (CD14++CD16+), and nonclassical (CD14+CD16++) monocytes may represent progressive stages of monocyte maturation or disparate myeloid lineages with different turnover rates and function. To investigate the relationship between monocyte subsets and the response to SIV infection, we performed microarray analysis of monocyte subsets in rhesus macaques at three time points: prior to SIV infection, 26 days postinfection, and necropsy with AIDS. Genes with a 2-fold change between monocyte subsets (2023 genes) or infection time points (424 genes) were selected. We identify 172 genes differentially expressed among monocyte subsets in both uninfected and SIV-infected animals. Classical monocytes express genes associated with inflammatory responses and cell proliferation. Nonclassical monocytes express genes associated with activation, immune effector functions, and cell cycle inhibition. The classical and intermediate subsets are most similar at all time points, and transcriptional similarity between intermediate and nonclassical monocytes increases with AIDS. Cytosolic sensors of nucleic acids, restriction factors, and IFN-stimulated genes are induced in all three subsets with AIDS. We conclude that SIV infection alters the transcriptional relationship between monocyte subsets and that the innate immune response to SIV infection is conserved across monocyte subsets.

Critical Role for Monocytes/Macrophages in Rapid Progression to AIDS in Pediatric Simian Immunodeficiency Virus-Infected Rhesus Macaques

Infant humans and rhesus macaques infected with the human or simian immunodeficiency virus (HIV or SIV), respectively, express higher viral loads and progress more rapidly to AIDS than infected adults. Activated memory CD4+ T cells in intestinal tissues are major primary target cells for SIV/HIV infection, and massive depletion of these cells is considered a major cause of immunodeficiency. Monocytes and macrophages are important cells of innate immunity and also are targets of HIV/SIV infection. We reported previously that a high peripheral blood monocyte turnover rate was predictive for the onset of disease progression to AIDS in SIV-infected adult macaques. The purpose of this study was to determine if earlier or higher infection of monocytes/macrophages contributes to the more rapid progression to AIDS in infants. We observed that uninfected infant rhesus macaques exhibited higher physiologic baseline monocyte turnover than adults. Early after SIV infection, the monocyte turnover further increased, and it remained high during progression to AIDS. A high percentage of terminal deoxynucleotidyltransferase dUTP nick end label (TUNEL)-positive macrophages in the lymph nodes (LNs) and intestine corresponded with an increasing number of macrophages derived from circulating monocytes (bromodeoxyuridine positive [BrdU+] CD163+), suggesting that the increased blood monocyte turnover was required to rapidly replenish destroyed tissue macrophages. Immunofluorescence analysis further demonstrated that macrophages were a significant portion of the virus-producing cells found in LNs, intestinal tissues, and lungs. The higher baseline monocyte turnover in infant macaques and subsequent macrophage damage by SIV infection may help explain the basis of more rapid disease progression to AIDS in infants.IMPORTANCE HIV infection progresses much more rapidly in pediatric cases than in adults; however, the mechanism for this difference is unclear. Using the rhesus macaque model, this work was performed to address why infants infected with SIV progress more quickly to AIDS than do adults. Earlier we reported that in adult rhesus macaques, increasing monocyte turnover reflected tissue macrophage damage by SIV and was predictive of terminal disease progression to AIDS. Here we report that uninfected infant rhesus macaques exhibited a higher physiological baseline monocyte turnover rate than adults. Furthermore, once infected with SIV, infants displayed further increased monocyte turnover that may have facilitated the accelerated progression to AIDS. These results support a role for monocytes and macrophages in the pathogenesis of SIV/HIV and begin to explain why infants are more prone to rapid disease progression.

HIV-1-Associated Atherosclerosis: Unraveling the Missing Link

Cardiovascular disease, including atherosclerosis and atherosclerosis-associated complications, is an increasing cause of morbidity and mortality in human immunodeficiency virus (HIV) patients in the post-antiretroviral therapy era. HIV alone accelerates atherosclerosis. Antiretroviral therapy; HIV-associated comorbidities, such as dyslipidemia, drug abuse, and opportunistic infections; and lifestyle are risk factors for HIV-associated atherosclerosis. However, our current understanding of HIV-associated atherogenesis is very limited and has largely been obtained from clinical observation. There is a pressing need to experimentally unravel the missing link between HIV and atherosclerosis. Understanding these mechanisms will help to better develop and design novel therapeutic interventions for the treatment of HIV-associated cardiovascular disease. HIV mainly infects T cells and macrophages resulting in the induction of oxidative and endoplasmic reticulum stress, the formation of the inflammasome, and the dysregulation of autophagy. These mechanisms may contribute to HIV-associated atherogenesis. In this review, we will summarize our current understanding and propose potential mechanisms of HIV-associated atherosclerosis.

Frontline Science: CXCR7 mediates CD14+CD16+ monocyte transmigration across the blood brain barrier: a potential therapeutic target for NeuroAIDS

CD14⁺CD16⁺ monocytes transmigrate into the CNS of HIV-positive people in response to chemokines elevated in the brains of infected individuals, including CXCL12. Entry of these cells leads to viral reservoirs, neuroinflammation, and neuronal damage. These may eventually lead to HIV-associated neurocognitive disorders. Although antiretroviral therapy (ART) has significantly improved the lives of HIV-infected people, the prevalence of cognitive deficits remains unchanged despite ART, still affecting >50% of infected individuals. There are no therapies to reduce these deficits or to prevent CNS entry of CD14⁺CD16⁺ monocytes. The goal of this study was to determine whether CXCR7, a receptor for CXCL12, is expressed on CD14⁺CD16⁺ monocytes and whether a small molecule CXCR7 antagonist (CCX771) can prevent CD14⁺CD16⁺ monocyte transmigration into the CNS. We showed for the first time that CXCR7 is on CD14⁺CD16⁺ monocytes and that it may be a therapeutic target to reduce their entry into the brain. We demonstrated that CD14⁺CD16⁺ monocytes and not the more abundant CD14⁺CD16^- monocytes or T cells transmigrate to low homeostatic levels of CXCL12. This may be a result of increased CXCR7 on CD14⁺CD16⁺ monocytes. We showed that CCX771 reduced transmigration of CD14⁺CD16⁺ monocytes but not of CD14⁺CD16^- monocytes from uninfected and HIV-infected individuals and that it reduced CXCL12-mediated chemotaxis of CD14⁺CD16⁺ monocytes. We propose that CXCR7 is a therapeutic target on CD14⁺CD16⁺ monocytes to limit their CNS entry, thereby reducing neuroinflammation, neuronal damage, and HIV-associated neurocognitive disorders. Our data also suggest that CCX771 may reduce CD14⁺CD16⁺ monocyte-mediated inflammation in other disorders.

Persistent accumulation of gut macrophages with impaired phagocytic function correlates with SIV disease progression in macaques

The contribution of macrophages in the gastrointestinal tract to disease control or progression in HIV infection remains unclear. To address this question, we analyzed CD163⁺ macrophages in ileum and mesenteric lymph nodes (LN) from SIV-infected rhesus macaques with dichotomous expression of controlling MHC class I alleles predicted to be SIV controllers or progressors. Infection induced accumulation of macrophages into gut mucosa in the acute phase that persisted in progressors but was resolved in controllers. In contrast, macrophage recruitment to mesenteric LNs occurred only transiently in acute infection irrespective of disease outcome. Persistent gut macrophage accumulation was associated with CD163 expression on α4β7⁺ CD16⁺ blood monocytes and correlated with epithelial damage. Macrophages isolated from intestine of progressors had reduced phagocytic function relative to controllers and uninfected macaques, and the proportion of phagocytic macrophages negatively correlated with mucosal epithelial breach, lamina propria Escherichia coli density, and plasma virus burden. Macrophages in intestine produced low levels of cytokines regardless of disease course, while mesenteric LN macrophages from progressors became increasingly responsive as infection advanced. These data indicate that noninflammatory CD163⁺ macrophages accumulate in gut mucosa in progressive SIV infection in response to intestinal damage but fail to adequately phagocytose debris, potentially perpetuating their recruitment.

Gut Mucosal Barrier Dysfunction, Microbial Dysbiosis, and Their Role in HIV-1 Disease Progression

Distinct pathological events occur within the gastrointestinal (GI) tract of Asian macaques with progressive simian immunodeficiency virus (SIV) infection and humans with human immunodeficiency virus type 1 (HIV-1) infection that are critical in shaping disease course. These events include depletion and functional alteration of GI-resident CD4(+) T cells, loss of antigen-presenting cells, loss of innate lymphocytes, and possible alterations to the composition of the gut microbiota. These contribute to structural damage to the GI tract and systemic translocation of GI tract microbial products. These translocated microbial products directly stimulate the immune system, and there is now overwhelming evidence that this drives chronic immune activation in HIV-1 and SIV infection. While combined antiretroviral therapy (cART) in HIV-1-infected subjects generally allows for immune reconstitution in peripheral blood, reconstitution of the GI tract occurs at a much slower pace, and both immunological and structural abnormalities persist in the GI tract. Importantly, studies of large cohorts of individuals have linked suboptimal GI reconstitution to residual inflammation and heightened morbidities in HIV-1-infected cART recipients. As a result, current era treatments aimed at augmenting restoration of the GI tract hold promise in returning cART recipients to full health.

Phenotype, function, and differentiation potential of human monocyte subsets

Human monocytes have been grouped into classical (CD14++CD16-), non-classical (CD14dimCD16++), and intermediate (CD14++CD16+) subsets. Documentation of normal function and variation in this complement of subtypes, particularly their differentiation potential to dendritic cells (DC) or macrophages, remains incomplete. We therefore phenotyped monocytes from peripheral blood of healthy subjects and performed functional studies on high-speed sorted subsets. Subset frequencies were found to be tightly controlled over time and across individuals. Subsets were distinct in their secretion of TNFα, IL-6, and IL-1β in response to TLR agonists, with classical monocytes being the most producers and non-classical monocytes the least. Monocytes, particularly those of the non-classical subtype, secreted interferon-α (IFN-α) in response to intracellular TLR3 stimulation. After incubation with IL-4 and GM-CSF, classical monocytes acquired monocyte-derived DC (mo-DC) markers and morphology and stimulated allogeneic T cell proliferation in MLR; intermediate and non-classical monocytes did not. After incubation with IL-3 and Flt3 ligand, no subset differentiated to plasmacytoid DC. After incubation with GM-CSF (M1 induction) or macrophage colony-stimulating factor (M-CSF) (M2 induction), all subsets acquired macrophage morphology, secreted macrophage-associated cytokines, and displayed enhanced phagocytosis. From these studies we conclude that classical monocytes are the principal source of mo-DCs, but all subsets can differentiate to macrophages. We also found that monocytes, in particular the non-classical subset, represent an alternate source of type I IFN secretion in response to virus-associated TLR agonists.

Balancing Trained Immunity with Persistent Immune Activation and the Risk of Simian Immunodeficiency Virus Infection in Infant Macaques Vaccinated with Attenuated Mycobacterium tuberculosis or Mycobacterium bovis BCG Vaccine

Our goal is to develop a pediatric combination vaccine to protect the vulnerable infant population against human immunodeficiency virus type 1 (HIV-1) and tuberculosis (TB) infections. The vaccine consists of an auxotroph Mycobacterium tuberculosis strain that coexpresses HIV antigens. Utilizing an infant rhesus macaque model, we have previously shown that this attenuated M. tuberculosis (AMtb)-simian immunodeficiency virus (SIV) vaccine is immunogenic, and although the vaccine did not prevent oral SIV infection, a subset of vaccinated animals was able to partially control virus replication. However, unexpectedly, vaccinated infants required fewer SIV exposures to become infected compared to naive controls. Considering that the current TB vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), can induce potent innate immune responses and confer pathogen-unspecific trained immunity, we hypothesized that an imbalance between enhanced myeloid cell function and immune activation might have influenced the outcome of oral SIV challenge in AMtb-SIV-vaccinated infants. To address this question, we used archived samples from unchallenged animals from our previous AMtb-SIV vaccine studies and vaccinated additional infant macaques with BCG or AMtb only. Our results show that vaccinated infants, regardless of vaccine strain or regimen, had enhanced myeloid cell responses. However, CD4+ T cells were concurrently activated, and the persistence of these activated target cells in oral and/or gastrointestinal tissues may have facilitated oral SIV infection. Immune activation was more pronounced in BCG-vaccinated infant macaques than in AMtb-vaccinated infant macaques, indicating a role for vaccine attenuation. These findings underline the importance of understanding the interplay of vaccine-induced immunity and immune activation and its effect on HIV acquisition risk and outcome in infants.

CD16+ Monocyte Subset Was Enriched and Functionally Exacerbated in Driving T-Cell Activation and B-Cell Response in Systemic Lupus Erythematosus

Background

The roles that CD16⁺ monocyte subset plays in T-cell activation and B-cell response have not been well studied in systemic lupus erythematosus (SLE).

Objective

The present study aimed to investigate the distribution of CD16⁺ monocyte subsets in SLE and explore their possible roles in T-cell activation and B-cell differentiation.

Methods

The frequencies of monocyte subsets in the peripheral blood of healthy controls (HCs) and patients with SLE were determined by flow cytometry. Monocyte subsets were sorted and cocultured with CD4⁺ T cells and CD19⁺ B cells. Then, T and B cells were collected for different subset detection, while the supernatants were collected for immunoglobulin G, IgA, and IgM or interferon-γ and interleukin-17A detection by enzyme-linked immunosorbent assay.

Results

Our results showed that CD16⁺ monocytes exhibited a proinflammatory phenotype with elevated CD80, CD86, HLA-DR, and CX3CR1 expression on the cell surface. It’s further demonstrated that CD16⁺ monocytes from patients and HCs shared different cell-surface marker profiles. The CD16⁺ subset was enriched in SLE and had an exacerbated capacity to promote CD4⁺ T cell polarization into a Th17 phenotype. Also, CD16⁺ monocytes had enhanced impacts on CD19⁺ B cells to differentiate into plasma B cells and regulatory B cells with more Ig production.

Conclusion

This study demonstrated that CD16⁺ monocytes, characterized by different cell-surface marker profiles, were enriched and played a critical role in driving the pathogenic T- and B-cell responses in patients with SLE.

Comprehensive panel of cross-reacting monoclonal antibodies for analysis of different immune cells and their distribution in the common marmoset (Callithrix jacchus)

BACKGROUND

Common marmosets are extensively used in immunological and pharmacological research, and the usage of methods such as flow cytometry gain increasing importance.

METHODS

Using multicolor flow cytometry cross-reactivity of monoclonal antibodies with cells of common marmosets was analyzed. Furthermore, frequencies of immune cells and immunological parameters were assessed in healthy common marmosets.

RESULTS

A total of 97 clones of monoclonal antibodies raised against CD markers, chemokine receptors, and miscellaneous markers were tested. Additionally, baseline frequencies of different innate and adaptive immune cells as well as certain parameters, such as activation and memory T-cell and B-cell distribution, are provided.

CONCLUSION

Our study gives an extended overview of cross-reactive antibodies for flow cytometric analysis of immune cells as well as baseline values for different immune parameters in healthy common marmosets.

Plasmacytoid dendritic cells and myeloid cells differently contribute to B-cell-activating factor belonging to the tumor necrosis factor superfamily overexpression during primary HIV infection

BACKGROUND

After describing heightened levels of circulating B-cell-activating factor belonging to the tumor necrosis factor superfamily (BAFF) as well as changes in B-cell phenotype and functions during acute infection by simian immunodeficiency virus, we wanted to determine whether and by which cells BAFF was over-expressed in primary HIV-infected (PHI) patients.

DESIGN AND METHODS

We simultaneously examined circulating BAFF levels by ELISA and membrane-bound BAFF (mBAFF) expression by flow cytometry in peripheral blood mononuclear cells of healthy donors and PHI patients followed for 6 months. We also examined whether HIV-1 modifies BAFF expression or release in various myeloid cells and plasmacytoid dendritic cells (pDC) in vitro.

RESULTS

Circulating BAFF levels were transiently increased at enrolment. They positively correlated with CXCL10 levels and inversely with B-cell counts. Whereas mBAFF was expressed by most pDC and on a fraction of intermediate monocytes in healthy donors, the frequency of mBAFF cells significantly increased among nonclassical monocytes and CD1c dendritic cells but decreased among pDC in PHI patients. In contrast to myeloid cells, pDC never released BAFF upon stimulation. Their mBAFF expression was enhanced by HIV-1, independently of type I IFN.

CONCLUSION

Our findings reveal that the pattern of BAFF expression by myeloid cells and pDC is altered in PHI patients and constitutes a valuable marker of immune activation whose circulating levels correlate with CXCL10 levels. Due to their homing in different tissue areas, pDC and myeloid cells might target different B-cell subsets through their mBAFF expression or soluble BAFF release.

Antiretroviral therapy in HIV-1-infected individuals with CD4 count below 100 cells/mm3 results in differential recovery of monocyte activation

Reversal of monocyte and macrophage activation and the relationship to viral suppression and T cell activation are unknown in patients with advanced HIV-1 infection, initiating antiretroviral therapy. This study aimed to determine whether reduction in biomarkers of monocyte and macrophage activation would be reduced in conjunction with viral suppression and resolution of T cell activation. Furthermore, we hypothesized that the addition of CCR5 antagonism (by maraviroc) would mediate greater reduction of monocyte/macrophage activation markers than suppressive antiretroviral therapy alone. In the CCR5 antagonism to decrease the incidence of immune reconstitution inflammatory syndrome study, antiretroviral therapy-naïve patients received maraviroc or placebo in addition to standard antiretroviral therapy. PBMCs and plasma from 65 patients were assessed during 24 wk of antiretroviral therapy for biomarkers of monocyte and macrophage activation. Markers of monocyte and macrophage activation were reduced significantly by 24 wk, including CD14(++)CD16(+) intermediate monocytes (P < 0.0001), surface CD163 (P = 0.0004), CD169 (P < 0.0001), tetherin (P = 0.0153), and soluble CD163 (P < 0.0001). A change in CD38(+), HLA-DR(+) CD8 T cells was associated with changes in CD169 and tetherin expression. Maraviroc did not affect biomarkers of monocyte/macrophage activation but resulted in greater percentages of CCR5-positive monocytes in PBMC. HIV-1 suppression after 24 wk of antiretroviral therapy, with or without maraviroc, demonstrates robust recovery in monocyte subset activation markers, whereas soluble markers of activation demonstrate minimal decrease, qualitatively differentiating markers of monocyte/macrophage activation in advanced disease.

Circulating monocytes: an appropriate model for bone-related study

Peripheral blood monocytes (PBMs) are an important source of precursors of osteoclasts, the bone-resorbing cells and the cytokines produced by PBMs that have profound effects on osteoclast differentiation, activation, and apoptosis. So PBMs represent a highly valuable and unique working cell model for bone-related study. Finding an appropriate working cell model for clinical and (epi-)genomic studies of human skeletal disorders is a challenge. Peripheral blood monocytes (PBMs) can give rise to osteoclasts, the bone-resorbing cells. Particularly, PBMs provide the sole source of osteoclast precursors for adult peripheral skeleton where the bone marrow is normally hematopoietically inactive. PBMs can secrete potent pro- and anti-inflammatory cytokines, which are important for osteoclast differentiation, activation, and apoptosis. Reduced production of PBM cytokines represents a major mechanism for the inhibitory effects of sex hormones on osteoclastogenesis and bone resorption. Abnormalities in PBMs have been linked to various skeletal disorders/traits, strongly supporting for the biological relevance of PBMs with bone metabolism and disorders. Here, we briefly review the origin and further differentiation of PBMs. In particular, we discuss the close relationship between PBMs and osteoclasts, and highlight the utility of PBMs in study the pathophysiological mechanisms underlying various skeletal disorders.

Blood Monocytes and Their Subsets: Established Features and Open Questions

In contrast to the past reliance on morphology, the identification and enumeration of blood monocytes are nowadays done with monoclonal antibodies and flow cytometry and this allows for subdivision into classical, intermediate, and non-classical monocytes. Using specific cell surface markers, dendritic cells in blood can be segregated from these monocytes. While in the past, changes in monocyte numbers as determined in standard hematology counters have not had any relevant clinical impact, the subset analysis now has uncovered informative changes that may be used in management of disease.

Differentiation Kinetics of Blood Monocytes and Dendritic Cells in Macaques: Insights to Understanding Human Myeloid Cell Development

Monocyte and dendritic cell (DC) development was evaluated using in vivo BrdU pulse-chase analyses in rhesus macaques, and phenotype analyses of these cells in blood also were assessed by immunostaining and flow cytometry for comparisons among rhesus, cynomolgus, and pigtail macaques, as well as African green monkeys and humans. The nonhuman primate species and humans have three subsets of monocytes, CD14(+)CD16(-), CD14(+)CD16(+), and CD14(-)CD16(+) cells, which correspond to classical, intermediate, and nonclassical monocytes, respectively. In addition, there exist presently two subsets of DC, BDCA-1(+) myeloid DC and CD123(+) plasmacytoid DC, that were first confirmed in rhesus macaque blood. Following BrdU inoculation, labeled cells first appeared in CD14(+)CD16(-) monocytes, then in CD14(+)CD16(+) cells, and finally in CD14(-)CD16(+) cells, thus defining different stages of monocyte maturation. A fraction of the classical CD14(+)CD16(-) monocytes gradually expressed CD16(+) to become CD16(+)CD14(+) cells and subsequently matured into the nonclassical CD14(-)CD16(+) cell subset. The differentiation kinetics of BDCA-1(+) myeloid DC and CD123(+) plasmacytoid DC were distinct from the monocyte subsets, indicating differences in their myeloid cell origins. Results from studies utilizing nonhuman primates provide valuable information about the turnover, kinetics, and maturation of the different subsets of monocytes and DC using approaches that cannot readily be performed in humans and support further analyses to continue examining the unique myeloid cell origins that may be applied to address disease pathogenesis mechanisms and intervention strategies in humans.

Increased Expression of CD169 on Blood Monocytes and Its Regulation by Virus and CD8 T Cells in Macaque Models of HIV Infection and AIDS

Increased expression of CD169 on monocytes has been reported in HIV-1-infected humans. Using rhesus macaque models of HIV infection, we sought to investigate whether simian immunodeficiency virus (SIV) infection upregulates CD169 expression on monocytes/macrophages. We also sought to determine whether CD8 T cells and plasma viral load directly impact the expression of CD169 on monocytes during SIV infection. We longitudinally assessed monocyte expression of CD169 during the course of SIV infection by flow cytometry, and examined the expression of CD169 on macrophages by immunohistochemistry in the spleen and lymph nodes of uninfected and infected macaques. CD169 expression on monocytes was substantially upregulated as early as 4 days during the hyperacute phase and peaked by 5-15 days after infection. After a transient decrease following the peak, its expression continued to increase during progression to AIDS. Monocyte CD169 expression was directly associated with plasma viral loads. To determine the contribution of CD8(+) T lymphocytes and virus to the control of monocyte CD169 expression, we used experimental CD8(+) lymphocyte depletion and antiretroviral therapy (ART) in SIV-infected macaques. Rapid depletion of CD8 T cells during acute infection of rhesus macaques induced an abrupt increase in CD169 expression. Importantly, levels of CD169 expression plummeted following initiation of ART and rebounded upon cessation of therapy. Taken together, our data reveal independent roles for virus and CD8(+) T lymphocytes in controlling monocyte CD169 expression, which may be an important link in further investigating the host response to viral infection.

Macrophage Polarization in AIDS: Dynamic Interface between Anti-Viral and Anti-Inflammatory Macrophages during Acute and Chronic Infection

Monocyte and macrophage inflammation in parenchymal tissues during acute and chronic HIV and SIV infection plays a role in early anti-viral immune responses and later in restorative responses. Macrophage polarization is observed in such responses in the central nervous system (CNS) and the heart and cardiac vessels that suggest early responses are M1 type antiviral responses, and later responses favor M2 restorative responses. Macrophage polarization is unique to different tissues and is likely dictated as much by the local microenvironment as well as other inflammatory cells involved in the viral responses. Such polarization is found in HIV infected humans, and the SIV infected animal model of AIDS, and occurs even with effective anti-retroviral therapy. Therapies that directly target macrophage polarization in HIV infection have recently been implemented, as have therapies to directly block traffic and accumulation of macrophages in tissues.

Eradication of HIV-1 from the macrophage reservoir: an uncertain goal?

Human immunodeficiency virus type 1 (HIV-1) establishes latency in resting memory CD4+ T cells and cells of myeloid lineage. In contrast to the T cells, cells of myeloid lineage are resistant to the HIV-1 induced cytopathic effect. Cells of myeloid lineage including macrophages are present in anatomical sanctuaries making them a difficult drug target. In addition, the long life span of macrophages as compared to the CD4+ T cells make them important viral reservoirs in infected individuals especially in the late stage of viral infection where CD4+ T cells are largely depleted. In the past decade, HIV-1 persistence in resting CD4+ T cells has gained considerable attention. It is currently believed that rebound viremia following cessation of combination anti-retroviral therapy (cART) originates from this source. However, the clinical relevance of this reservoir has been questioned. It is suggested that the resting CD4+ T cells are only one source of residual viremia and other viral reservoirs such as tissue macrophages should be seriously considered. In the present review we will discuss how macrophages contribute to the development of long-lived latent reservoirs and how macrophages can be used as a therapeutic target in eradicating latent reservoir.

Altered antigen-presenting cells during HIV-1 infection

PURPOSE OF REVIEW

The purpose of this study is to describe the alterations that HIV-1 induces in antigen-presenting cells (APCs), in vitro, ex vivo and in vivo.

RECENT FINDINGS

HIV-1 disarms several arms of the immune system including APCs. We summarize here recent findings on the impact of the virus on APC.

SUMMARY

HIV-1 can invade APC and overall reduce their capacity to present antigens effectively, mostly by reducing their numbers and inducing permanent hyperactivation. This occurs via a combination of alterations; however, the host can counteract, at least in part, some of these defects via restriction factors, autophagy, the production of type I interferon, antiviral cytokines, among others. However, these specific mechanisms of viral evasion from APCs' control lead to a chronic hyperactivation of the immune system implicated in AIDS-related and non-AIDS related pathogenesis. Unfortunately, the current regimens of antiretroviral therapy are unable to dampen sufficiently APC-driven viral-induced immune hyperactivation. Understanding how HIV alters APC will help to tune appropriately both intrinsic immunity and innate immunity, as well as achieve efficient antigen presentation to the adaptive immune system, without inducing a detrimental pervasive hyperactivation of the immune system.

Clinical significance of monocyte heterogeneity

Monocytes are primitive hematopoietic cells that primarily arise from the bone marrow, circulate in the peripheral blood and give rise to differentiated macrophages. Over the past two decades, considerable attention to monocyte diversity and macrophage polarization has provided contextual clues into the role of myelomonocytic derivatives in human disease. Until recently, human monocytes were subdivided based on expression of the surface marker CD16. "Classical" monocytes express surface markers denoted as CD14(++)CD16(-) and account for greater than 70% of total monocyte count, while "non-classical" monocytes express the CD16 antigen with low CD14 expression (CD14(+)CD16(++)). However, recognition of an intermediate population identified as CD14(++)CD16(+) supports the new paradigm that monocytes are a true heterogeneous population and careful identification of specific subpopulations is necessary for understanding monocyte function in human disease. Comparative studies of monocytes in mice have yielded more dichotomous results based on expression of the Ly6C antigen. In this review, we will discuss the use of monocyte subpopulations as biomarkers of human disease and summarize correlative studies in mice that may yield significant insight into the contribution of each subset to disease pathogenesis.

Glucocorticoid treatment at moderate doses of SIVmac251-infected rhesus macaques decreases the frequency of circulating CD14+CD16++ monocytes but does not alter the tissue virus reservoir

Subsets of CD16-positive monocytes produce proinflammatory cytokines and expand during chronic infection with the human immunodeficiency virus type 1 (HIV). HIV-infected macrophage in tissues may be long lived and contribute to the establishment and maintenance of the HIV reservoir. We found that the (intermediate) CD14(++)CD16(+) and (nonclassical) CD14(+)CD16(++) monocyte subsets are significantly expanded during infection of Rhesus macaques with pathogenic SIV(mac251) but not during infection of sooty mangabeys with the nonpathogenic isolate SIVSM. In vitro glucocorticoid (GC) treatment of peripheral blood mononuclear cells (PBMCs) from uninfected or SIV(mac251)-infected Rhesus macaques and HIV-infected patients treated or not with antiretroviral therapy (ART) resulted in a significant decrease in the frequency of both CD16-positive monocyte subsets. Short-term in vivo treatment with high doses of GC of chronically SIV(mac251)-infected macaques resulted in a significant decrease in the CD14(+)CD16(++) population and, to a lesser extent, in the CD14(++)CD16(+) monocytes, as well as a significant decrease in the number of macrophages in tissues. Surprisingly, treatment of SIV(mac251)-infected macaques with ART significantly increased the CD14(++)CD16(+) population and the addition of GC resulted in a significant decrease in only the CD14(+)CD16(++) subset. No difference in SIV DNA levels in blood, lymph nodes, gut, and spleen was found between the groups treated with ART or ART plus GC. Thus, it appears that high doses of GC treatment in the absence of ART could affect both CD16-positive populations in vivo. Whether the efficacy of this treatment at higher doses to decrease virus levels outweighs its risks remains to be determined.

Shift in monocyte apoptosis with increasing viral load and change in apoptosis-related ISG/Bcl2 family gene expression in chronically HIV-1-infected subjects

Although monocytes and macrophages are targets of HIV-1-mediated immunopathology, the impact of high viremia on activation-induced monocyte apoptosis relative to monocyte and macrophage activation changes remains undetermined. In this study, we determined constitutive and oxidative stress-induced monocyte apoptosis in uninfected and HIV(+) individuals across a spectrum of viral loads (n = 35; range, 2,243 to 1,355,998 HIV-1 RNA copies/ml) and CD4 counts (range, 26 to 801 cells/mm(3)). Both constitutive apoptosis and oxidative stress-induced apoptosis were positively associated with viral load and negatively associated with CD4, with an elevation in apoptosis occurring in patients with more than 40,000 (4.6 log) copies/ml. As expected, expression of Rb1 and interferon-stimulated genes (ISGs), plasma soluble CD163 (sCD163) concentration, and the proportion of CD14(++) CD16(+) intermediate monocytes were elevated in viremic patients compared to those in uninfected controls. Although CD14(++) CD16(+) frequencies, sCD14, sCD163, and most ISG expression were not directly associated with a change in apoptosis, sCD14 and ISG expression showed an association with increasing viral load. Multivariable analysis of clinical values and monocyte gene expression identified changes in IFI27, IFITM2, Rb1, and Bcl2 expression as determinants of constitutive apoptosis (P = 3.77 × 10(-5); adjusted R(2) = 0.5983), while changes in viral load, IFITM2, Rb1, and Bax expression were determinants of oxidative stress-induced apoptosis (P = 5.59 × 10(-5); adjusted R(2) = 0.5996). Our data demonstrate differential activation states in monocytes between levels of viremia in association with differences in apoptosis that may contribute to greater monocyte turnover with high viremia.

IMPORTANCE

This study characterized differential monocyte activation, apoptosis, and apoptosis-related gene expression in low- versus high-level viremic HIV-1 patients, suggesting a shift in apoptosis regulation that may be associated with disease state. Using single and multivariable analysis of monocyte activation parameters and gene expression, we supported the hypothesis that monocyte apoptosis in HIV disease is a reflection of viremia and activation state with contributions from gene expression changes within the ISG and Bcl2 gene families. Understanding monocyte apoptosis response may inform HIV immunopathogenesis, retention of infected macrophages, and monocyte turnover in low- or high-viral-load states.

Spatiotemporal dynamics of simian immunodeficiency virus brain infection in CD8+ lymphocyte-depleted rhesus macaques with neuroAIDS

Despite the success of combined antiretroviral therapy in controlling viral replication in human immunodeficiency virus (HIV)-infected individuals, HIV-associated neurocognitive disorders, commonly referred to as neuroAIDS, remain a frequent and poorly understood complication. Infection of CD8(+) lymphocyte-depleted rhesus macaques with the SIVmac251 viral swarm is a well-established rapid disease model of neuroAIDS that has provided critical insight into HIV-1-associated neurocognitive disorder onset and progression. However, no studies so far have characterized in depth the relationship between intra-host viral evolution and pathogenesis in this model. Simian immunodeficiency virus (SIV) env gp120 sequences were obtained from six infected animals. Sequences were sampled longitudinally from several lymphoid and non-lymphoid tissues, including individual lobes within the brain at necropsy, for four macaques; two animals were sacrificed at 21 days post-infection (p.i.) to evaluate early viral seeding of the brain. Bayesian phylodynamic and phylogeographic analyses of the sequence data were used to ascertain viral population dynamics and gene flow between peripheral and brain tissues, respectively. A steady increase in viral effective population size, with a peak occurring at ~50-80 days p.i., was observed across all longitudinally monitored macaques. Phylogeographic analysis indicated continual viral seeding of the brain from several peripheral tissues throughout infection, with the last migration event before terminal illness occurring in all macaques from cells within the bone marrow. The results strongly supported the role of infected bone marrow cells in HIV/SIV neuropathogenesis. In addition, our work demonstrated the applicability of Bayesian phylogeography to intra-host studies in order to assess the interplay between viral evolution and pathogenesis.

Physiopathology of necrobiotic xanthogranuloma with monoclonal gammopathy

RATIONALE

Xanthomatosis associated with monoclonal gammopathy includes hyperlipidaemic xanthoma (HX), normolipidaemic xanthoma (NX) and necrobiotic xanthogranuloma (NXG). All three pathologies are characterized by skin or visceral lesions related to cholesterol accumulation, monoclonal immunoglobulin (MIg) and hypocomplementemia. The pathophysiology underlying NXG remains unknown although the involvement of MIg is suspected.

OBJECTIVE

To provide further insights into the pathophysiology of NXG, we evaluated the plasma lipid phenotype, mechanisms involved in cellular cholesterol accumulation and role of MIg in an analysis of blood and plasma markers of inflammation in 16 patients with xanthomatosis [NXG (n = 8) and NX (n = 8)] associated with monoclonal IgG relative to the relevant controls.

RESULTS

The lipid profile of patients with NXG was characterized by a low HDL-C phenotype and an abnormal distribution of HDL particles. Sera from patients with NXG induced cholesterol accumulation in human macrophages. This accumulation was due in part to a significant reduction in the HDL capacity to promote cholesterol efflux from macrophages, which was not found in the case of NX. The MIg of NXG and NX patients was tested positively by ELISA to recognize a large spectrum of lipoproteins. High plasma levels of pro-inflammatory cytokines (TNFα and IL-6), soluble cytokine receptors (sIL-6R, sTNFRI and sTNFRII), adhesion molecules (VCAM-1 and ICAM-1) and chemokines (MCP-1, IL-8 and MIP-1α) were observed in both patients with NXG and NX, revealing a specific xanthoma inflammatory signature which was inversely correlated with plasma levels of anti-inflammatory HDL. However, patients with NXG were distinguished by elevated levels of IL-15 and a marked increase in the rate of intermediate CD14++CD16+ monocytes.

CONCLUSION

This study revealed that NXG is characterized by impaired macrophage lipid homeostasis associated with a systemic inflammatory profile that may result from the interaction of MIg and lipoproteins.