CD16+ monocyte subset preferentially harbors HIV-1 and is expanded in pregnant Malawian women with Plasmodium falciparum malaria and HIV-1 infection

Cerebrospinal fluid CD14++CD16+ monocytes in HIV-1 subtype C compared with subtype B

CD14++CD16+ monocytes are susceptible to HIV-1 infection, and cross the blood-brain barrier. HIV-1 subtype C (HIV-1C) shows reduced Tat protein chemoattractant activity compared to HIV-1B, which might influence monocyte trafficking into the CNS. We hypothesized that the proportion of monocytes in CSF in HIV-1C is lower than HIV-1B group. We sought to assess differences in monocyte proportions in cerebrospinal fluid (CSF) and peripheral blood (PB) between people with HIV (PWH) and without HIV (PWoH), and by HIV-1B and -C subtypes. Immunophenotyping was performed by flow cytometry, monocytes were analyzed within CD45 + and CD64 + gated regions and classified in classical (CD14++CD16-), intermediate (CD14++CD16+), and non-classical (CD14lowCD16+). Among PWH, the median [IQR] CD4 nadir was 219 [32-531] cell/mm3; plasma HIV RNA (log10) was 1.60 [1.60-3.21], and 68% were on antiretroviral therapy (ART). Participants with HIV-1C and -B were comparable in terms of age, duration of infection, CD4 nadir, plasma HIV RNA, and ART. The proportion of CSF CD14++CD16+ monocytes was higher in participants with HIV-1C than those with HIV-1B [2.00(0.00-2.80) vs. 0.00(0.00-0.60) respectively, p = 0.03 after BH correction p = 0.10]. Despite viral suppression, the proportion of total monocytes in PB increased in PWH, due to the increase in CD14++CD16+ and CD14lowCD16+ monocytes. The HIV-1C Tat substitution (C30S31) did not interfere with the migration of CD14++CD16+ monocytes to the CNS. This is the first study to evaluate these monocytes in the CSF and PB and compare their proportions according to HIV subtype.

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.

HIV-1-induced type I IFNs promote viral latency in macrophages

Macrophages chronically infected with HIV-1 serve as a reservoir that contributes to HIV-1 persistence during antiretroviral therapy; however, the mechanisms governing the establishment and maintenance of this virus reservoir have not been fully elucidated. Here, we show that HIV-1 enters a state reminiscent of latency in monocyte-derived macrophages (MDMs), characterized by integrated proviral DNA with decreased viral transcription. This quiescent state is associated with decreased NF-κB p65, RNA polymerase II, and p-TEFb recruitment to the HIV-1 promoter as well as maintenance of promoter chromatin in a transcriptionally nonpermissive state. MDM transition to viral latency is mediated by type I IFN signaling, as inhibiting type I IFN signaling or blocking type 1 IFN prevents the establishment of latent infection. Knockdown studies demonstrate that the innate immune signaling molecule mitochondrial antiviral signaling protein (MAVS) is required for the transition to latency. Finally, we demonstrate a role for the viral accessory protein Vpr in the establishment of HIV-1 latency in macrophages. Our data indicate that HIV-1-induced type I IFN production is responsible for the establishment of viral latency in MDMs and identify possible therapeutic targets for the prevention or elimination of this important HIV-1 reservoir.

HIV Latency in Myeloid Cells: Challenges for a Cure

The use of antiretroviral therapy (ART) for Human Immunodeficiency Virus (HIV) treatment has been highly successful in controlling plasma viremia to undetectable levels. However, a complete cure for HIV is hindered by the presence of replication-competent HIV, integrated in the host genome, that can persist long term in a resting state called viral latency. Resting memory CD4+ T cells are considered the biggest reservoir of persistent HIV infection and are often studied exclusively as the main target for an HIV cure. However, other cell types, such as circulating monocytes and tissue-resident macrophages, can harbor integrated, replication-competent HIV. To develop a cure for HIV, focus is needed not only on the T cell compartment, but also on these myeloid reservoirs of persistent HIV infection. In this review, we summarize their importance when designing HIV cure strategies and challenges associated to their identification and specific targeting by the “shock and kill” approach.

Genetic and cytometric analyses of subcutaneous adipose tissue in patients with hemophilia and HIV-associated lipodystrophy

Background

The authors recently performed plastic surgeries for a small number of patients with hemophilia, HIV infection, and morphologic evidence of lipodystrophy. Because the pathophysiological mechanism of HIV-associated lipodystrophy remains to be elucidated, we analyzed subcutaneous adipose tissues from the patients.

Methods

All six patients had previously been treated with older nucleoside analogue reverse-transcriptase inhibitors (NRTIs; stavudine, didanosine or zidovudine). Abdominal and inguinal subcutaneous fat samples were obtained from the HIV+ patients with hemophilia and HIV− healthy volunteers (n = 6 per group), and analyzed via DNA microarray, real-time PCR, flow cytometry and immunohistochemistry.

Results

The time from initial NRTI treatment to collecting samples were 21.7 years in average. Cytometric analysis revealed infiltration of inflammatory M1 macrophages into HIV-infected adipose tissue and depletion of adipose-derived stem cells, possibly due to exhaustion following sustained adipocyte death. Genetic analysis revealed that adipose tissue from HIV+ group had increased immune activation, mitochondrial toxicity, chronic inflammation, progressive fibrosis and adipocyte dysfunction (e.g. insulin resistance, inhibited adipocyte differentiation and accelerated apoptosis). Of note, both triglyceride synthesis and lipolysis were inhibited in adipose tissue from patients with HIV.

Conclusions

Our findings provide important insights into the pathogenesis of HIV-associated lipodystrophy, suggesting that fat redistribution may critically depend on adipocytes’ sensitivity to drug-induced mitochondrial toxicity, which may lead either to atrophy or metabolic complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12981-022-00432-9.

Persistent Inflammation and Non-AIDS Comorbidities During ART: Coming of the Age of Monocytes

Monocytes are innate immune cells that serve as the first line of defense against pathogens by engulfing and destroying pathogens or by processing and presenting antigens to initiate adaptive immunity and stimulate immunological responses. Monocytes are classified into three types: classical, intermediate, and non-classical monocytes, each of which plays a particular function in response to pathogens. Human immunodeficiency virus type 1 (HIV-1) infection disrupts the balance of monocyte subsets, and the quantity and function of monocytes will not fully recover even with long-term antiretroviral therapy (ART). Monocytes are vital for the establishment and maintenance of HIV-1 latent viral reservoirs and are closely related to immune dysfunction even after ART. Therefore, the present review focuses on the phenotypic function of monocytes and their functions in HIV-1 infection to elucidate their roles in HIV patients.

RALDH Activity Induced by Bacterial/Fungal Pathogens in CD16+ Monocyte-Derived Dendritic Cells Boosts HIV Infection and Outgrowth in CD4+ T Cells

HIV reservoirs persist in gut-homing CD4⁺ T cells of people living with HIV and receiving antiretroviral therapy, but the antigenic specificity of such reservoirs remains poorly documented. The imprinting for gut homing is mediated by retinoic acid (RA), a vitamin A-derived metabolite produced by dendritic cells (DCs) exhibiting RA-synthesizing (RALDH) activity. RALDH activity in DCs can be induced by TLR2 ligands, such as bacterial peptidoglycans and fungal zymosan. Thus, we hypothesized that bacterial/fungal pathogens triggering RALDH activity in DCs fuel HIV reservoir establishment/outgrowth in pathogen-reactive CD4⁺ T cells. Our results demonstrate that DCs derived from intermediate/nonclassical CD16⁺ compared with classical CD16^- monocytes exhibited superior RALDH activity and higher capacity to transmit HIV infection to autologous Staphylococcus aureus-reactive T cells. Exposure of total monocyte-derived DCs (MDDCs) to S. aureus lysates as well as TLR2 (zymosan and heat-killed preparation of Listeria monocytogenes) and TLR4 (LPS) agonists but not CMV lysates resulted in a robust upregulation of RALDH activity. MDDCs loaded with S. aureus or zymosan induced the proliferation of T cells with a CCR5⁺integrin β7⁺CCR6⁺ phenotype and efficiently transmitted HIV infection to these T cells via RALDH/RA-dependent mechanisms. Finally, S. aureus- and zymosan-reactive CD4⁺ T cells of antiretroviral therapy-treated people living with HIV carried replication-competent integrated HIV-DNA, as demonstrated by an MDDC-based viral outgrowth assay. Together, these results support a model in which bacterial/fungal pathogens in the gut promote RALDH activity in MDDCs, especially in CD16⁺ MDDCs, and subsequently imprint CD4⁺ T cells with gut-homing potential and HIV permissiveness. Thus, nonviral pathogens play key roles in fueling HIV reservoir establishment/outgrowth via RALDH/RA-dependent mechanisms that may be therapeutically targeted.

Central Nervous System (CNS) Viral Seeding by Mature Monocytes and Potential Therapies To Reduce CNS Viral Reservoirs in the cART Era

We characterized mechanisms of CNS viral reservoir establishment/replenishment using peripheral blood mononuclear cells (PBMC) of PLWH on cART and propose therapeutic targets to reduce/block selective entry of cells harboring HIV (HIV⁺) into the CNS. Using DNA/RNAscope, we show that CD14⁺ CD16⁺ monocytes with integrated HIV, transcriptionally active, and/or with active viral replication from PBMC of PLWH prescribed cART and virally suppressed, selectively transmigrate across a human BBB model.

The human immunodeficiency virus (HIV) enters the central nervous system (CNS) within a few days after primary infection, establishing viral reservoirs that persist even with combined antiretroviral therapy (cART). We show that monocytes from people living with HIV (PLWH) on suppressive cART harboring integrated HIV, viral mRNA, and/or viral proteins preferentially transmigrate across the blood-brain barrier (BBB) to CCL2 and are significantly enriched post-transmigration, and even more highly enriched posttransmigration than T cells with similar properties. Using HIV-infected ART-treated mature monocytes cultured in vitro, we recapitulate these findings and demonstrate that HIV⁺ CD14⁺ CD16⁺ ART-treated monocytes also preferentially transmigrate. Cenicriviroc and anti-JAM-A and anti-ALCAM antibodies significantly and preferentially reduce/block transmigration of HIV⁺ CD14⁺ CD16⁺ ART-treated monocytes. These findings highlight the importance of monocytes in CNS HIV reservoirs and suggest targets to eliminate their formation and reseeding.

Increased Monocyte Inflammatory Responses to Oxidized LDL Are Associated with Insulin Resistance in HIV-Infected Individuals on Suppressive Antiretroviral Therapy

Despite long term antiretroviral therapy (ART), insulin resistance (IR) is common among people living with HIV/AIDS (PLWHA) exposing this population to a greater risk of cardiometabolic complications when compared to their uninfected counterparts. We previously identified an expansion in monocyte subpopulations in blood that were linked to the degree of IR in persons with HIV on stable ART. In this study, we directly assessed monocyte inflammatory functional properties from PLWHA on ART (n = 33) and HIV-uninfected controls (n = 14) of similar age, gender, and cardiovascular disease risk and determined the relationship with IR (homeostatic model assessment-insulin resistance (HOMA-IR)), calculated from fasting blood glucose and insulin measurements. Peripheral blood mononuclear cells were stimulated with oxidized low-density lipoproteins (oxLDL) and polyfunctional monocyte cytokine responses (IL-1β, IL-6, IL-8, or TNF-α) were determined by flow cytometry. Higher monocyte IL-1β and IL-8 responses to oxLDL were associated with higher IR in PLWHA but not in the control group. We observed that higher basal monocyte cytokine responses were associated with both duration since HIV diagnosis and ART initiation. In the management of IR in chronic HIV, strategies lowering monocyte IL-1β and IL-8 responses should be considered in addition to ART in order to limit adverse cardio-metabolic outcomes.

Macrophage Polarization in Leprosy-HIV Co-infected Patients

In HIV-infected individuals, a paradoxical clinical deterioration may occur in preexisting leprosy when highly active antiretroviral therapy (HAART)-associated reversal reaction (RR) develops. Leprosy–HIV co-infected patients during HAART may present a more severe form of the disease (RR/HIV), but the immune mechanisms related to the pathogenesis of leprosy–HIV co-infection remain unknown. Although the adaptive immune responses have been extensively studied in leprosy–HIV co-infected individuals, recent studies have described that innate immune cells may drive the overall immune responses to mycobacterial antigens. Monocytes are critical to the innate immune system and play an important role in several inflammatory conditions associated with chronic infections. In leprosy, different tissue macrophage phenotypes have been associated with the different clinical forms of the disease, but it is not clear how HIV infection modulates the phenotype of innate immune cells (monocytes or macrophages) during leprosy. In the present study, we investigated the phenotype of monocytes and macrophages in leprosy–HIV co-infected individuals, with or without RR. We did not observe differences between the monocyte profiles in the studied groups; however, analysis of gene expression within the skin lesion cells revealed that the RR/HIV group presents a higher expression of macrophage scavenger receptor 1 (MRS1), CD209 molecule (CD209), vascular endothelial growth factor (VEGF), arginase 2 (ARG2), and peroxisome proliferator-activated receptor gamma (PPARG) when compared with the RR group. Our data suggest that different phenotypes of tissue macrophages found in the skin from RR and RR/HIV patients could differentially contribute to the progression of leprosy.

Transcriptional profiling and immunophenotyping show sustained activation of blood monocytes in subpatent Plasmodium falciparum infection

OBJECTIVES

Malaria, caused by Plasmodium infection, remains a major global health problem. Monocytes are integral to the immune response, yet their transcriptional and functional responses in primary Plasmodium falciparum infection and in clinical malaria are poorly understood.

METHODS

The transcriptional and functional profiles of monocytes were examined in controlled human malaria infection with P. falciparum blood stages and in children and adults with acute malaria. Monocyte gene expression and functional phenotypes were examined by RNA sequencing and flow cytometry at peak infection and compared to pre-infection or at convalescence in acute malaria.

RESULTS

In subpatent primary infection, the monocyte transcriptional profile was dominated by an interferon (IFN) molecular signature. Pathways enriched included type I IFN signalling, innate immune response and cytokine-mediated signalling. Monocytes increased TNF and IL-12 production upon in vitro toll-like receptor stimulation and increased IL-10 production upon in vitro parasite restimulation. Longitudinal phenotypic analyses revealed sustained significant changes in the composition of monocytes following infection, with increased CD14⁺CD16^- and decreased CD14^-CD16⁺ subsets. In acute malaria, monocyte CD64/FcγRI expression was significantly increased in children and adults, while HLA-DR remained stable. Although children and adults showed a similar pattern of differentially expressed genes, the number and magnitude of gene expression change were greater in children.

CONCLUSIONS

Monocyte activation during subpatent malaria is driven by an IFN molecular signature with robust activation of genes enriched in pathogen detection, phagocytosis, antimicrobial activity and antigen presentation. The greater magnitude of transcriptional changes in children with acute malaria suggests monocyte phenotypes may change with age or exposure.

Infrequent HIV Infection of Circulating Monocytes during Antiretroviral Therapy

Whereas human immunodeficiency virus (HIV) persists in tissue macrophages during antiretroviral therapy (ART), the role of circulating monocytes as HIV reservoirs remains controversial. Three magnetic bead selection methods and flow cytometry cell sorting were compared for their capacity to yield pure CD14⁺ monocyte populations. Cell sorting by flow cytometry provided the purest population of monocytes (median CD4⁺ T-cell contamination, 0.06%), and the levels of CD4⁺ T-cell contamination were positively correlated with the levels of integrated HIV DNA in the monocyte populations. Using cell sorting by flow cytometry, we assessed longitudinally the infection of monocytes and other cell subsets in a cohort of 29 Thai HIV-infected individuals. Low levels of HIV DNA were detected in a minority of monocyte fractions obtained before and after 1 year of ART (27% and 33%, respectively), whereas HIV DNA was readily detected in CD4⁺ T cells from all samples. Additional samples (2 to 5 years of ART) were obtained from 5 individuals in whom monocyte infection was previously detected. Whereas CD4⁺ T cells were infected at high levels at all time points, monocyte infection was inconsistent and absent in at least one longitudinal sample from 4/5 individuals. Our results indicate that infection of monocytes is infrequent and highlight the importance of using flow cytometry cell sorting to minimize contamination by CD4⁺ T cells.IMPORTANCE The role of circulating monocytes as persistent HIV reservoirs during ART is still controversial. Several studies have reported persistent infection of monocytes in virally suppressed individuals; however, others failed to detect HIV in this subset. These discrepancies are likely explained by the diversity of the methods used to isolate monocytes and to detect HIV infection. In this study, we show that only flow cytometry cell sorting yields a highly pure population of monocytes largely devoid of CD4 contaminants. Using this approach in a longitudinal cohort of HIV-infected individuals before and during ART, we demonstrate that HIV is rarely found in monocytes from untreated and treated HIV-infected individuals. This study highlights the importance of using methods that yield highly pure populations of cells as flow cytometry cell sorting to minimize and control for CD4⁺ T-cell contamination.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of “shock and kill” to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current “shock and kill” strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

The impact of substance abuse on HIV-mediated neuropathogenesis in the current ART era

Approximately 37 million people worldwide are infected with human immunodeficiency virus (HIV). One highly significant complication of HIV infection is the development of HIV-associated neurocognitive disorders (HAND) in 15-55% of people living with HIV (PLWH), that persists even in the antiretroviral therapy (ART) era. The entry of HIV into the central nervous system (CNS) occurs within 4-8 days after peripheral infection. This establishes viral reservoirs that may persist even in the presence of ART. Once in the CNS, HIV infects resident macrophages, microglia, and at low levels, astrocytes. In response to chronic infection and cell activation within the CNS, viral proteins, inflammatory mediators, and host and viral neurotoxic factors produced over extended periods of time result in neuronal injury and loss, cognitive deficits and HAND. Substance abuse is a common comorbidity in PLWH and has been shown to increase neuroinflammation and cognitive disorders. Additionally, it has been associated with poor ART adherence, and increased viral load in the cerebrospinal fluid (CSF), that may also contribute to increased neuroinflammation and neuronal injury. Studies have examined mechanisms that contribute to neuroinflammation and neuronal damage in PLWH, and how substances of abuse exacerbate these effects. This review will focus on how substances of abuse, with an emphasis on methamphetamine (meth), cocaine, and opioids, impact blood brain barrier (BBB) integrity and transmigration of HIV-infected and uninfected monocytes across the BBB, as well as their effects on monocytes/macrophages, microglia, and astrocytes within the CNS. We will also address how these substances of abuse may contribute to HIV-mediated neuropathogenesis in the context of suppressive ART. Additionally, we will review the effects of extracellular dopamine, a neurotransmitter that is increased in the CNS by substances of abuse, on HIV neuropathogenesis and how this may contribute to neuroinflammation, neuronal insult, and HAND in PLWH with active substance use. Lastly, we will discuss some potential therapies to limit CNS inflammation and damage in HIV-infected substance abusers.

HIV-1 is rarely detected in blood and colon myeloid cells during viral-suppressive antiretroviral therapy

OBJECTIVE

The aim of this study was to explore the contribution of blood and colon myeloid cells to HIV persistence during antiretroviral therapy (ART).

DESIGN

Leukapheresis was collected from HIV-infected individuals with undetectable plasma viral load during ART (HIV + ART; n = 15) and viremics untreated (HIV+; n = 6). Rectal sigmoid biopsies were collected from n = 8 HIV+ART.

METHODS

Myeloid cells (total monocytes (Mo), CD16/CD16 Mo, CD1c dendritic cells) and CD4 T cells were isolated by magnetic-activated cell sorting (MACS) and/or fluorescence-activated cell sorting (FACS) from peripheral blood. Matched myeloid and CCR6CD4 T cells were isolated from blood and rectal biopsies by FACS. Levels of early (RU5 primers), late (Gag primers) and/or integrated HIV-DNA (Alu/HIV primers) were quantified by nested real-time PCR. Replication-competent HIV was amplified by co-culturing cells from HIV-positive individuals with CD3/CD28-activated CD4 T cells from uninfected donors.

RESULTS

Early/late but not integrated HIV reverse transcripts were detected in blood myeloid subsets of four out of 10 HIV+ART; in contrast, integrated HIV-DNA was exclusively detected in CD4 T cells. In rectal biopsies, late HIV reverse transcripts were detected in myeloid cells and CCR6CD4 T cells from one out of eight and seven out of eight HIV+ART individuals, respectively. Replication-competent HIV was outgrown from CD4 T cells but not from myeloid of untreated/ART-treated HIV-positive individuals.

CONCLUSION

In contrast to CD4 T cells, blood and colon myeloid cells carry detectable HIV only in a small fraction of HIV+ART individuals. This is consistent with the documented resistance of Mo to HIV infection and the rapid turnover of Mo-derived macrophages in the colon. Future assessment of multiple lymphoid and nonlymphoid tissues is required to include/exclude myeloid cells as relevant HIV reservoirs during ART.

How Monocytes Contribute to Increased Risk of Atherosclerosis in Virologically-Suppressed HIV-Positive Individuals Receiving Combination Antiretroviral Therapy

Combination antiretroviral therapy (ART) is effective at suppressing HIV viremia to achieve persistently undetectable levels in peripheral blood in the majority of individuals with access and ability to maintain adherence to treatment. However, evidence suggests that ART is less effective at eliminating HIV-associated inflammation and innate immune activation. To the extent that residual inflammation and immune activation persist, virologically suppressed people living with HIV (PLWH) may have increased risk of inflammatory co-morbidities, and adjunctive therapies may need to be considered to reduce HIV-related inflammation and fully restore the health of virologically suppressed HIV+ individuals. Cardiovascular disease (CVD) is the single leading cause of death in the developed world and is becoming more important in PLWH with access to ART. Arterial disease due to atherosclerosis, leading to acute myocardial infarction (AMI) and stroke, is a major component of CVD. Atherosclerosis is an inflammatory disease, and epidemiological comparisons of atherosclerosis and AMI show a higher prevalence and suggest a greater risk in PLWH compared to the general population. The reasons for greater prevalence of CVD in PLWH can be broadly grouped into four categories: (a) the higher prevalence of traditional risk factors e.g., smoking and hypertension (b) dyslipidemia (also a traditional risk factor) caused by off-target effects of ART drugs (c) HIV-related inflammation and immune activation and (d) other undefined HIV-related factors. Management strategies aimed at reducing the impact of traditional risk factors in PLWH are similar to those for the general population and their effectiveness is currently being evaluated. Together with improvements in ART regimens and guidelines for treatment, and a greater awareness of its impact on CVD, the HIV-related risk of AMI and stroke is decreasing but remains elevated compared to the general community. Monocytes are key effector cells which initiate the formation of atherosclerotic plaques by migrating into the intima of coronary arteries and accumulating as foam cells full of lipid droplets. This review considers the specific role of monocytes as effector cells in atherosclerosis which progresses to AMI and stroke, and explores mechanisms by which HIV may promote an atherogenic phenotype and function independent of traditional risk factors. Altered monocyte function may represent a distinct HIV-related factor which increases risk of CVD in PLWH.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of "shock and kill" to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current "shock and kill" strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

Experimental severe malaria is resolved by targeting newly-identified monocyte subsets using immune-modifying particles combined with artesunate

Current treatment of severe malaria and associated cerebral malaria (CM) and respiratory distress syndromes are directed primarily at the parasite. Targeting the parasite has only partial efficacy in advanced infection, as neurological damage and respiratory distress are due to accumulation of host blood cells in the brain microvasculature and lung interstitium. Here, computational analysis identifies Ly6C^lo monocytes as a major component of the immune infiltrate in both organs in a preclinical mouse model. Specifically targeting Ly6C^lo monocyte precursors, identified by adoptive transfer, with immune-modifying particles (IMP) prevents experimental CM (ECM) in 50% of Plasmodium berghei ANKA-infected mice in early treatment protocols. Furthermore, treatment at onset of clinical ECM with 2 doses of a novel combination of IMP and anti-malarial drug artesunate results in 88% survival. This combination confers protection against ECM and mortality in late stage severe experimental malaria and provides a viable advance on current treatment regimens.

Adipose Tissue T Cells in HIV/SIV Infection

Adipose tissue comprises one of the largest organs in the body and performs diverse functions including energy storage and release, regulation of appetite and other neuroendocrine signaling, and modulation of immuity, among others. Adipocytes reside in a complex compartment where antigen, antigen presenting cells, innate immune cells, and adaptive immune cells interact locally and exert systemic effects on inflammation, circulating immune cell profiles, and metabolic homeostasis. T lymphocytes are a major component of the adipose tissue milieu which are altered in disease states such as obesity and human immunodeficiency virus (HIV) infection. While obesity, HIV infection, and simian immunodeficiency virus (SIV; a non-human primate virus similar to HIV) infection are accompanied by enrichment of CD8⁺ T cells in the adipose tissue, major phenotypic differences in CD4⁺ T cells and other immune cell populations distinguish HIV/SIV infection from obesity. Furthermore, DNA and RNA species of HIV and SIV can be detected in the stromal vascular fraction of visceral and subcutaneous adipose tissue, and replication-competent HIV resides in local CD4⁺ T cells. Here, we review studies of adipose tissue CD4⁺ and CD8⁺ T cell populations in HIV and SIV, and contrast the findings with those reported in obesity.

Human interleukin-34-derived macrophages have increased resistance to HIV-1 infection

The establishment of latent HIV-1 reservoirs in terminally differentiated cells represents a major impediment to the success of antiretroviral therapies. Notably, macrophages (Mϕs) are susceptible to HIV-1 infection and recent evidence suggests that they may be involved in long-term HIV-1 persistence. While the extensive functional heterogeneity seen across the Mϕ cell lineage parallels the spectrum of HIV-1 susceptibility reported across these cell subsets, the facets of Mϕ HIV-1 resistance and susceptibility remain to be fully defined. Notably, the differentiation of most Mϕ subsets depends on signaling through the macrophage colony-stimulating factor receptor (M-CSFR), which in addition to M-CSF, is now known to bind the unrelated interleukin-34 (IL-34) cytokine. The biological need for two M-CSFR ligands awaits full elucidation. Here, we report that Mϕs differentiated from human peripheral blood monocytes with IL-34 are substantially more resistant to HIV-1 infection than M-CSF-derived Mϕs. Moreover, while both Mϕ subsets express comparable surface protein levels of the HIV-1 receptor and co-receptor, CD4 and CCR5 respectively, the IL-34-Mϕs express significantly greater levels of pertinent restriction factor genes, potentially accounting for their greater resistance to HIV-1 infection than that observed in M-CSF-Mϕs. Together, our findings underline previously unexplored differentiation pathways resulting in HIV-1-susceptible and resistant Mϕ subsets and pave the way for further research that may overcome one of the last major hurdles in developing more successful antiretroviral therapy.

Peering into the HIV reservoir

The main obstacle to HIV eradication is the establishment of a long-term persistent HIV reservoir. Although several therapeutic approaches have been developed to reduce and eventually eliminate the HIV reservoir, only a few have achieved promising results. A better knowledge of the mechanisms involved in the establishment and maintenance of HIV reservoir is of utmost relevance for the design of new therapeutic strategies aimed at purging it with the ultimate goal of achieving HIV eradication or alternatively a functional cure. In this regard, it is also important to take a close look into the cellular HIV reservoirs other than resting memory CD4 T-cells with key roles in reservoir maintenance that have been recently described. Unraveling the special characteristics of these HIV cellular compartments could aid us in designing new therapeutic strategies to deplete the latent HIV reservoir.

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.

Mechanisms of CNS Viral Seeding by HIV+ CD14+ CD16+ Monocytes: Establishment and Reseeding of Viral Reservoirs Contributing to HIV-Associated Neurocognitive Disorders

HIV reservoirs persist despite antiretroviral therapy (ART) and are established within a few days after infection. Infected myeloid cells in the central nervous system (CNS) may contribute to the establishment of a CNS viral reservoir. The mature CD14⁺ CD16⁺ monocyte subset enters the CNS in response to chemokines, including CCL2. Entry of infected CD14⁺ CD16⁺ monocytes may lead to infection of other CNS cells, including macrophages or microglia and astrocytes, and to release of neurotoxic early viral proteins and additional cytokines. This contributes to neuroinflammation and neuronal damage leading to HIV-associated neurocognitive disorders (HAND) in ~50% of HIV-infected individuals despite ART. We examined the mechanisms of monocyte entry in the context of HIV infection and report for the first time that HIV⁺ CD14⁺ CD16⁺ monocytes preferentially transmigrate across the blood-brain barrier (BBB). The junctional proteins JAM-A and ALCAM and the chemokine receptor CCR2 are essential to their preferential transmigration across the BBB to CCL2. We show here that JAM-A and ALCAM are increased on HIV⁺ CD14⁺ CD16⁺ monocytes compared to their expression on HIV^exp CD14⁺ CD16⁺ monocytes-cells that are uninfected but exposed to HIV, viral proteins, and inflammatory mediators. Antibodies against JAM-A and ALCAM and the novel CCR2/CCR5 dual inhibitor cenicriviroc prevented or significantly reduced preferential transmigration of HIV⁺ CD14⁺ CD16⁺ monocytes. This indicates that JAM-A, ALCAM, and CCR2 may be potential therapeutic targets to block entry of these infected cells into the brain and prevent or reduce the establishment and replenishment of viral reservoirs within the CNS.IMPORTANCE HIV infects different tissue compartments of the body, including the central nervous system (CNS). This leads to establishment of viral reservoirs within the CNS that mediate neuroinflammation and neuronal damage, contributing to cognitive impairment. Our goal was to examine the mechanisms of transmigration of cells that contribute to HIV infection of the CNS and to continued replenishment of CNS viral reservoirs, to establish potential therapeutic targets. We found that an HIV-infected subset of monocytes, mature HIV⁺ CD14⁺ CD16⁺ monocytes, preferentially transmigrates across the blood-brain barrier. This was mediated, in part, by increased junctional proteins JAM-A and ALCAM and chemokine receptor CCR2. We show that the CCR2/CCR5 dual inhibitor cenicriviroc and blocking antibodies against the junctional proteins significantly reduce, and often completely block, the transmigration of HIV⁺ CD14⁺ CD16⁺ monocytes. This suggests new opportunities to eliminate infection and seeding or reseeding of viral reservoirs within the CNS, thus reducing neuroinflammation, neuronal damage, and cognitive impairment.

Human Primary Macrophages Derived In Vitro from Circulating Monocytes Comprise Adherent and Non-Adherent Subsets with Differential Expression of Siglec-1 and CD4 and Permissiveness to HIV-1 Infection

Macrophages are a major target for human immunodeficiency virus type 1 (HIV-1) infection. However, macrophages are largely heterogeneous and may exhibit differences in permissiveness to HIV-1 infection. This study highlights the interplay of macrophage heterogeneity in HIV-1 pathogenesis. We show that monocyte-derived macrophages (MDMs) could be divided into two distinct subsets: CD14⁺Siglec-1^hiCD4⁺ (non-adherent MDM) and CD14⁺Siglec-1^LoCD4⁻ (adherent MDM). The CD14⁺Siglec-1^hiCD4⁺MDM subset represented the smaller proportion in the macrophage pool, and varied among different donors. Fractionation and subsequent exposure of the two MDM subsets to HIV-1 revealed opposite outcomes in terms of HIV-1 capture and infection. Although the CD14⁺Siglec-1^hiCD4⁺MDM captured significantly more HIV-1, infection was significantly higher in the CD14⁺Siglec-1^LoCD4⁻MDM subset. Thus, CD14⁺Siglec-1^hiCD4⁺MDM were less permissive to infection. Depletion of CD14⁺Siglec-1^hiCD4⁺MDM or a decrease in their percentage, resulted in increased infection of MDM, suggestive of a capacity of these cells to capture and sequester HIV-1 in an environment that hinders its infectivity. Increased expression of innate restriction factors and cytokine genes were observed in the non-adherent CD14⁺Siglec-1^hiCD4⁺MDM, both before and after HIV-1 infection, compared to the adherent CD14⁺Siglec-1^LoCD4⁻MDM. We speculate that the differential expression of gene expression profiles in the two macrophage subsets may provide an explanation for the differences observed in HIV-1 infectivity.

Monocyte dysregulation and systemic inflammation during pediatric falciparum malaria

BACKGROUND

Inflammation and monocytes are thought to be important to human malaria pathogenesis. However, the relationship of inflammation and various monocyte functions to acute malaria, recovery from acute malaria, and asymptomatic parasitemia in endemic populations is poorly understood.

METHODS

We evaluated plasma cytokine levels, monocyte subsets, monocyte functional responses, and monocyte inflammatory transcriptional profiles of 1- to 10-year-old Kenyan children at the time of presentation with acute uncomplicated malaria and at recovery 6 weeks later; these results were compared with analogous data from asymptomatic children and adults in the same community.

RESULTS

Acute malaria was marked by elevated levels of proinflammatory and regulatory cytokines and expansion of the inflammatory "intermediate" monocyte subset that returned to levels of healthy asymptomatic children 6 weeks later. Monocytes displayed activated phenotypes during acute malaria, with changes in surface expression of markers important to innate and adaptive immunity. Functionally, acute malaria monocytes and monocytes from asymptomatic infected children had impaired phagocytosis of P. falciparum-infected erythrocytes relative to asymptomatic children with no blood-stage infection. Monocytes from both acute malaria and recovery time points displayed strong and equivalent cytokine responsiveness to innate immune agonists that were independent of infection status. Monocyte transcriptional profiles revealed regulated and balanced proinflammatory and antiinflammatory and altered phagocytosis gene expression patterns distinct from malaria-naive monocytes.

CONCLUSION

These observations provide insights into monocyte functions and the innate immune response during uncomplicated malaria and suggest that asymptomatic parasitemia in children is not clinically benign.

FUNDING

Support for this work was provided by NIH/National Institute of Allergy and Infectious Diseases (R01AI095192-05), the Burroughs Wellcome Fund/American Society of Tropical Medicine and Hygiene, and the Rainbow Babies & Children's Foundation.

Adipose Tissue in HIV Infection

HIV infection and antiretroviral therapy (ART) treatment exert diverse effects on adipocytes and stromal-vascular fraction cells, leading to changes in adipose tissue quantity, distribution, and energy storage. A HIV-associated lipodystrophic condition was recognized early in the epidemic, characterized by clinically apparent changes in subcutaneous, visceral, and dorsocervical adipose depots. Underlying these changes is altered adipose tissue morphology and expression of genes central to adipocyte maturation, regulation, metabolism, and cytokine signaling. HIV viral proteins persist in circulation and locally within adipose tissue despite suppression of plasma viremia on ART, and exposure to these proteins impairs preadipocyte maturation and reduces adipocyte expression of peroxisome proliferator-activated receptor gamma (PPAR-γ) and other genes involved in cell regulation. Several early nucleoside reverse transcriptase inhibitor and protease inhibitor antiretroviral drugs demonstrated substantial adipocyte toxicity, including reduced mitochondrial DNA content and respiratory chain enzymes, reduced PPAR-γ and other regulatory gene expression, and increased proinflammatory cytokine production. Newer-generation agents, such as integrase inhibitors, appear to have fewer adverse effects. HIV infection also alters the balance of CD4+ and CD8+ T cells in adipose tissue, with effects on macrophage activation and local inflammation, while the presence of latently infected CD4+ T cells in adipose tissue may constitute a protected viral reservoir. This review provides a synthesis of the literature on how HIV virus, ART treatment, and host characteristics interact to affect adipose tissue distribution, immunology, and contribution to metabolic health, and adipocyte maturation, cellular regulation, and energy storage. © 2017 American Physiological Society. Compr Physiol 7:1339-1357, 2017.

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.

Reprint of: Alterations of TRIM21-mRNA expression during monocyte maturation

Tripartite motif-containing protein 21 (TRIM21) play a dual role in the cytoplasm of the cells where it facilitates destruction of some antibody-coated viruses and some bacteria, and initiates synthesis of proinflammatory cytokines. Macrophages and CD16⁺ monocyte subset can particularly participate in a proinflammatory response caused by viral infection, however, the molecular mechanisms underlying these processes are not fully understood. The aim of this study was to determine the level of TRIM21-mRNA expression in monocyte subsets including: classical (CD14⁺⁺CD16^-), intermediate (CD14⁺⁺CD16⁺) and non-classical (CD14⁺CD16⁺⁺) monocytes, as well as during in vitro differentiation of the isolated monocytes towards dendritic cells or macrophages. Our results revealed that the level of TRIM21 mRNA expression was significantly lower in CD16- monocytes, when compared to CD16⁺ cells and the whole monocyte population, yet no significant differences were observed when CD16⁺ population was divided into intermediate and non-classical subsets. More pronounced differences were observed in the case of monocyte-derived macrophages (MDM) and dendritic cells (DCs). TRIM21-mRNA expression level was app. 6-fold higher in DCs, and app. 16-fold higher in MDM (p<0,01), when compared to freshly isolated monocytes. Our results may suggest the new mechanism of increased proinflammatory cytokine production by CD16⁺ (intermediate and non-classical) monocytes and macrophages, at least in patients with acute or chronic infections, caused by enveloped viruses. We suggest that TRIM21 may be one of the factors associated with the "switching on" the proinflammatory programme in CD16⁺ monocytes or monocyte-derived macrophages.

Monocyte subtypes and the CCR2 chemokine receptor in cardiovascular disease

Monocytes circulate in the blood and migrate to inflammatory tissues, but their functions can be either detrimental or beneficial, depending on their phenotypes. In humans, classical monocytes are inflammatory cluster of differentiation (CD)14++CD16−CCR2++ cells originated from the bone marrow or spleen reservoirs and comprise ≥92% of monocytes. Intermediate monocytes (CD14++CD16+CCR2+) are involved in the production of anti-inflammatory cytokines [such as interleukin (IL)-10], reactive oxygen species (ROS), and proinflammatory mediators [such as tumor necrosis factor-α (TNF-α) and IL-1β). Nonclassical monocytes (CD14+CD16++CCR2−) are patrolling cells involved in tissue repair and debris removal from the vasculature. Many studies in both humans and animals have shown the importance of monocyte chemoattractant protein-1 (MCP-1) and its receptor [chemokine receptor of MCP-1 (CCR2)] in pathologies, such as atherosclerosis and myocardial infarction (MI). This review presents the importance of these monocyte subsets in cardiovascular diseases (CVDs), and sheds light on new strategies for the blocking of the MCP-1/CCR2 axis as a therapeutic goal for treating vascular disorders.

HIV-associated neurocognitive disorders: recent advances in pathogenesis, biomarkers, and treatment

HIV-associated neurocognitive disorders (HAND) remain prevalent despite plasma viral suppression by antiretroviral agents. In fact, the prevalence of milder subtypes of cognitive impairment is increasing. Neuropsychologic testing remains the "gold standard" of diagnosis; however, this is time consuming and costly in a resource-poor environment. Recently developed screening tools, such as CogState and the revised HIV dementia scale, have very good sensitivity and specificity in the more severe stages of HAND. However, questions remain regarding the utility of, optimal population for, and insensitivity of tests in mild HAND. Recognition of ongoing viral persistence and the inflammatory milieu in the central nervous system (CNS) has advanced our understanding of the pathogenesis of HAND and facilitated the development of biomarkers of CNS disease. The importance of the monocyte-macrophage lineage cell and the astrocyte as viral reservoirs, HIV viral proteins, self-perpetuating CNS inflammation, and CCR5 chemokine receptor neurotropism has been identified. Whilst biomarkers demonstrate monocyte activation, inflammation, and neuronal injury, they remain limited in their clinical utility. The improved understanding of pathogenic mechanisms has led to novel approaches to the treatment of HAND; however, despite these advances, the optimal management is still undefined.

Dopamine Increases CD14+CD16+ Monocyte Transmigration across the Blood Brain Barrier: Implications for Substance Abuse and HIV Neuropathogenesis

In human immunodeficiency virus-1 (HIV) infected individuals, substance abuse may accelerate the development and/or increase the severity of HIV associated neurocognitive disorders (HAND). It is proposed that CD14⁺CD16⁺ monocytes mediate HIV entry into the central nervous system (CNS) and that uninfected and infected CD14⁺CD16⁺ monocyte transmigration across the blood brain barrier (BBB) contributes to the establishment and propagation of CNS HIV viral reservoirs and chronic neuroinflammation, important factors in the development of HAND. The effects of substance abuse on the frequency of CD14⁺CD16⁺ monocytes in the peripheral circulation and on the entry of these cells into the CNS during HIV neuropathogenesis are not known. PBMC from HIV infected individuals were analyzed by flow cytometry and we demonstrate that the frequency of peripheral blood CD14⁺CD16⁺ monocytes in HIV infected substance abusers is increased when compared to those without active substance use. Since drug use elevates extracellular dopamine concentrations in the CNS, we examined the effects of dopamine on CD14⁺CD16⁺ monocyte transmigration across our in vitro model of the human BBB. The transmigration of this monocyte subpopulation is increased by dopamine and the dopamine receptor agonist, SKF 38393, implicating D1-like dopamine receptors in the increase in transmigration elicited by this neurotransmitter. Thus, elevated extracellular CNS dopamine may be a novel common mechanism by which active substance use increases uninfected and HIV infected CD14⁺CD16⁺ monocyte transmigration across the BBB. The influx of these cells into the CNS may increase viral seeding and neuroinflammation, contributing to the development of HIV associated neurocognitive impairments.

Alterations of TRIM21-mRNA expression during monocyte maturation

Tripartite motif-containing protein 21 (TRIM21) play a dual role in the cytoplasm of the cells where it facilitates destruction of some antibody-coated viruses and some bacteria, and initiates synthesis of proinflammatory cytokines. Macrophages and CD16⁺ monocyte subset can particularly participate in a proinflammatory response caused by viral infection, however, the molecular mechanisms underlying these processes are not fully understood. The aim of this study was to determine the level of TRIM21-mRNA expression in monocyte subsets including: classical (CD14⁺⁺CD16^-), intermediate (CD14⁺⁺CD16⁺) and non-classical (CD14⁺CD16⁺⁺) monocytes, as well as during in vitro differentiation of the isolated monocytes towards dendritic cells or macrophages. Our results revealed that the level of TRIM21 mRNA expression was significantly lower in CD16- monocytes, when compared to CD16⁺ cells and the whole monocyte population, yet no significant differences were observed when CD16⁺ population was divided into intermediate and non-classical subsets. More pronounced differences were observed in the case of monocyte-derived macrophages (MDM) and dendritic cells (DCs). TRIM21-mRNA expression level was app. 6-fold higher in DCs, and app. 16-fold higher in MDM (p<0,01), when compared to freshly isolated monocytes. Our results may suggest the new mechanism of increased proinflammatory cytokine production by CD16⁺ (intermediate and non-classical) monocytes and macrophages, at least in patients with acute or chronic infections, caused by enveloped viruses. We suggest that TRIM21 may be one of the factors associated with the "switching on" the proinflammatory programme in CD16⁺ monocytes or monocyte-derived macrophages.

Macrophages in Progressive Human Immunodeficiency Virus/Simian Immunodeficiency Virus Infections

The cells that are targeted by primate lentiviruses (HIV and simian immunodeficiency virus [SIV]) are of intense interest given the renewed effort to identify potential cures for HIV. These viruses have been reported to infect multiple cell lineages of hematopoietic origin, including all phenotypic and functional CD4 T cell subsets. The two most commonly reported cell types that become infected in vivo are memory CD4 T cells and tissue-resident macrophages. Though viral infection of CD4 T cells is routinely detected in both HIV-infected humans and SIV-infected Asian macaques, significant viral infection of macrophages is only routinely observed in animal models wherein CD4 T cells are almost entirely depleted. Here we review the roles of macrophages in lentiviral disease progression, the evidence that macrophages support viral replication in vivo, the animal models where macrophage-mediated replication of SIV is thought to occur, how the virus can interact with macrophages in vivo, pathologies thought to be attributed to viral replication within macrophages, how viral replication in macrophages might contribute to the asymptomatic phase of HIV/SIV infection, and whether macrophages represent a long-lived reservoir for the virus.

The Effect of Malaria and HIV Co-Infection on Anemia: A Meta-Analysis

Malaria and human immunodeficiency virus (HIV) infections are globally important public health concerns. The objectives of this study were (i) to determine the prevalence of malaria and HIV co-infections in people living in endemic countries, and (ii) to assess the effect of co-infection on anemia.Studies were searched on electronic databases including PubMed, Embase, Medline, Google Scholar, and African Journals Online. Observational studies, assessing the prevalence of co-infection and reporting its association with anemia, were included. The methodological quality of included studies was assessed using a tool called the risk of bias assessment for non-randomized studies. Heterogeneity among studies was investigated with the I-square test. Pooled prevalence of the co-infection and its 95% confidence interval (CI) were estimated using the random-effect model, reflected on heterogeneity among studies. Summary odds ratio (OR), summary standardized mean difference (SMD), and their corresponding 95% CIs were estimated, as appropriate. Subgroup analysis and meta-regression were performed for robustness of results. Publication bias was assessed by visualization of a funnel plot.Twenty-three studies were included in the present study. Overall, the pooled prevalence of co-infection was 19% (95% CI: 15-23%, I: 98.1%), showing 26% (95% CI: 20-32%, I: 98.7%) in adults, 12% (95% CI: 7-17%, I: 95.0) in pregnant women, and 9% (95% CI: 6-11%, I: 68.6%) in children. Anemia was comparable between the monoinfected and co-infected adults (summary OR: 1.49, 95% CI: 0.93-2.37) and increased by 49% in co-infected pregnant women (summary OR: 1.49, 95% CI: 1.14-1.94). The mean hemoglobin concentration was significantly lower in the co-infected group than the monoinfected group (summary SMD: -0.47, 95% CI: -0.61 to -0.33). The results of meta-regression on the prevalence of co-infection using the publication year and total population as covariates showed the I value remained high implying a de facto random distribution of heterogeneity. An asymmetrical funnel plot indicated the presence of publication bias. Due to heterogeneity of the studies in this review, the results have to be interpreted with caution.The findings of this study suggest that the prevalence of malaria and HIV co-infection, particularly in pregnant women, requires special attention from healthcare personnel. Better understanding of the co-infection is crucial for designing treatment strategies. Future well-powered, prospective designs assessing the interaction between malaria and HIV are recommended.

Statin modulation of monocyte phenotype and function: implications for HIV-1-associated neurocognitive disorders

HIV-1-associated neurocognitive disorder (HAND) remains a persistent problem despite antiretroviral therapy (ART), largely a result of continued inflammation in the periphery and the brain and neurotoxin release from activated myeloid cells in the CNS. CD14+CD16+ inflammatory monocytes, expanded in HIV infection, play a central role in the pathogenesis of HAND and have parallels with monocyte-dependent inflammatory mechanisms in atherosclerosis. Statins, through their HMG-CoA reductase inhibitor activity, have pleiotropic immunomodulatory properties that contribute to their benefit in atherosclerosis beyond lipid lowering. Here, we investigated whether statins would modulate the monocyte phenotype and function associated with HIV-1 neuropathogenesis. Treatment ex vivo with simvastatin and atorvastatin reduced the proportion of CD16+ monocytes in peripheral blood mononuclear cells, as well as in purified monocytes, especially CD14++CD16+ "intermediate" monocytes most closely associated with neurocognitive disease. Statin treatment also markedly reduced expression of CD163, which is also linked to HAND pathogenesis. Finally, simvastatin inhibited production of monocyte chemoattractant protein-1 (MCP-1) and other inflammatory cytokines following LPS stimulation and reduced monocyte chemotaxis in response to MCP-1, a major driver of myeloid cell accumulation in the CNS in HAND. Together, these findings suggest that statin drugs may be useful to prevent or reduce HAND in HIV-1-infected subjects on ART with persistent monocyte activation and inflammation.

Associations between Cognition, Gender and Monocyte Activation among HIV Infected Individuals in Nigeria

The potential role of gender in the occurrence of HIV-related neurocognitive impairment (NCI) and associations with markers of HIV-related immune activity has not been previously examined. In this study 149 antiretroviral-naïve seropositive subjects in Nigeria (SP, 92 women and 57 men) and 58 seronegative (SN, 38 women and 20 men) were administered neuropsychological testing that assessed 7 ability domains. From the neuropsychological test scores was calculated a global deficit score (GDS), a measure of overall NCI. Percentages of circulating monocytes and plasma HIV RNA, soluble CD163 and soluble CD14 levels were also assessed. HIV SP women were found to be younger, more educated and had higher CD4+ T cell counts and borderline higher viral load measures than SP men. On the neuropsychological testing, SP women were more impaired in speed of information processing and verbal fluency and had a higher mean GDS than SN women. Compared to SP men, SP women were also more impaired in speed of information processing and verbal fluency as well as on tests of learning and memory. Numbers of circulating monocytes and plasma sCD14 and sCD163 levels were significantly higher for all SP versus all SN individuals and were also higher for SP women and for SP men versus their SN counterparts. Among SP women, soluble CD14 levels were slightly higher than for SP men, and SP women had higher viral load measurements and were more likely to have detectable virus than SP men. Higher sCD14 levels among SP women correlated with more severe global impairment, and higher viral load measurements correlated with higher monocyte numbers and sCD14 and sCD14 levels, associations that were not observed for SP men. These studies suggest that the risk of developing NCI differ for HIV infected women and men in Nigeria and, for women, may be linked to effects from higher plasma levels of HIV driving activation of circulating monocytes.

Fatal Pediatric Cerebral Malaria Is Associated with Intravascular Monocytes and Platelets That Are Increased with HIV Coinfection

Cerebral malaria (CM) is a major contributor to malaria deaths, but its pathophysiology is not well understood. While sequestration of parasitized erythrocytes is thought to be critical, the roles of inflammation and coagulation are controversial. In a large series of Malawian children hospitalized with CM, HIV coinfection was more prevalent than in pediatric population estimates (15% versus 2%, P < 0.0001, chi-square test), with higher mortality than that seen in HIV-uninfected children (23% versus 17%, P = 0.0178, chi-square test). HIV-infected (HIV⁺) children with autopsy-confirmed CM were older than HIV-uninfected children (median age, 99 months versus 32 months, P = 0.0007, Mann-Whitney U test) and appeared to lack severe immunosuppression. Because HIV infection is associated with dysregulated inflammation and platelet activation, we performed immunohistochemistry analysis for monocytes, platelets, and neutrophils in brain tissue from HIV⁺ and HIV-uninfected children with fatal CM. Children with autopsy-confirmed CM had significantly (>9 times) more accumulations of intravascular monocytes and platelets, but not neutrophils, than did children with nonmalarial causes of coma. The monocyte and platelet accumulations were significantly (>2-fold) greater in HIV⁺ children than in HIV-uninfected children with autopsy-confirmed CM. Our findings indicate that HIV is a risk factor for CM and for death from CM, independent of traditional measures of HIV disease severity. Brain histopathology supports the hypotheses that inflammation and coagulation contribute to the pathogenesis of pediatric CM and that immune dysregulation in HIV⁺ children exacerbates the pathological features associated with CM.

Importance  There are nearly 1 million malaria deaths yearly, primarily in sub-Saharan African children. Cerebral malaria (CM), marked by coma and sequestered malaria parasites in brain blood vessels, causes half of these deaths, although the mechanisms causing coma and death are uncertain. Sub-Saharan Africa has a high HIV prevalence, with 3 million HIV-infected (HIV⁺) children, but the effects of HIV on CM pathogenesis and mortality are unknown. In a study of pediatric CM in Malawi, HIV prevalence was high and CM-attributed mortality was higher in HIV⁺ than in HIV-uninfected children. Brain pathology in children with fatal CM was notable not only for sequestered malaria parasites but also for intravascular accumulations of monocytes and platelets that were more severe in HIV⁺ children. Our findings raise the possibility that HIV⁺ children at risk for malaria may benefit from targeted malaria prophylaxis and that adjunctive treatments targeting inflammation and/or coagulation may improve CM outcomes.

There are nearly 1 million malaria deaths yearly, primarily in sub-Saharan African children. Cerebral malaria (CM), marked by coma and sequestered malaria parasites in brain blood vessels, causes half of these deaths, although the mechanisms causing coma and death are uncertain. Sub-Saharan Africa has a high HIV prevalence, with 3 million HIV-infected (HIV⁺) children, but the effects of HIV on CM pathogenesis and mortality are unknown. In a study of pediatric CM in Malawi, HIV prevalence was high and CM-attributed mortality was higher in HIV⁺ than in HIV-uninfected children. Brain pathology in children with fatal CM was notable not only for sequestered malaria parasites but also for intravascular accumulations of monocytes and platelets that were more severe in HIV⁺ children. Our findings raise the possibility that HIV⁺ children at risk for malaria may benefit from targeted malaria prophylaxis and that adjunctive treatments targeting inflammation and/or coagulation may improve CM outcomes.

Plasmodium falciparum Infection of Human Volunteers Activates Monocytes and CD16+ Dendritic Cells and Induces Upregulation of CD16 and CD1c Expression

Antigen-presenting cells (APCs) are key players in the induction and regulation of immune responses. In Plasmodium falciparum malaria, determination of which cells and pathways are activated in the network of APCs remains elusive. We therefore investigated the effects of a controlled human malaria infection in healthy, malaria-naive volunteers on the subset composition and activation status of dendritic cells (DCs) and monocytes. While subsets of monocytes increased in frequency during blood-stage infection, DC frequencies remained largely stable. Activation markers classically associated with peptide presentation to and priming of αβT cells, HLA-DR and CD86, were upregulated in monocytes and inflammatory CD16 myeloid DCs (mDCs) but not in the classical CD1c, BDCA2, or BDCA3 DC subsets. In addition, these activated APC subsets showed increased expression of CD1c, which is involved in glycolipid antigen presentation, and of the immune complex binding Fcγ receptor III (CD16). Our data show that P. falciparum asexual parasites do not activate classical DC subsets but instead activate mainly monocytes and inflammatory CD16 mDCs and appear to prime alternative activation pathways via induction of CD16 and/or CD1c. Changes in expression of these surface molecules might increase antigen capture and enhance glycolipid antigen presentation in addition to the classical major histocompatibility complex class II (MHC-II) peptide presentation and thereby contribute to the initiation of T-cell responses in malaria. (This study has been registered at Clinicaltrials.gov under registration no. NCT01086917.).

Insights into end-organ injury in HIV infection: dynamics of monocyte trafficking to the brain in SIV encephalitis

This commentary highlights the article by Nowlin et al, which explores the dynamic roles of macrophages in early and late central nervous system lentiviral disease.

Distinct phenotype, longitudinal changes of numbers and cell-associated virus in blood dendritic cells in SIV-infected CD8-lymphocyte depleted macaques

Loss of circulating CD123+ plasmacytoid dendritic cells (pDCs) during HIV infection is well established. However, changes of myeloid DCs (mDCs) are ambiguous since they are studied as a homogeneous CD11c+ population despite phenotypic and functional heterogeneity. Heterogeneity of CD11c+ mDCs in primates is poorly described in HIV and SIV infection. Using multiparametric flow cytometry, we monitored longitudinally cell number and cell-associated virus of CD123+ pDCs and non-overlapping subsets of CD1c+ and CD16+ mDCs in SIV-infected CD8-depleted rhesus macaques. The numbers of all three DC subsets were significantly decreased by 8 days post-infection. Whereas CD123+ pDCs were persistently depleted, numbers of CD1c+ and CD16+ mDCs rebounded. Numbers of CD1c+ mDCs significantly increased by 3 weeks post-infection while numbers of CD16+ mDCs remained closer to pre-infection levels. We found similar changes in the numbers of all three DC subsets in CD8 depleted animals as we found in animals that were SIV infected animals that were not CD8 lymphocyte depleted. CD16+ mDCs and CD123+ pDCs but not CD1c+ mDCs were significantly decreased terminally with AIDS. All DC subsets harbored SIV RNA as early as 8 days and then throughout infection. However, SIV DNA was only detected in CD123+ pDCs and only at 40 days post-infection consistent with SIV RNA, at least in mDCs, being surface-bound. Altogether our data demonstrate that SIV infection differently affects CD1c+ and CD16+ mDCs where CD16+ but not CD1c+ mDCs are depleted and might be differentially regulated in terminal AIDS. Finally, our data underline the importance of studying CD1c+ and CD16+ mDCs as discrete populations, and not as total CD11c+ mDCs.

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.

The importance of monocytes and macrophages in HIV pathogenesis, treatment, and cure

Monocytes and macrophages play critical roles in HIV transmission, viral spread early in infection, and as a reservoir of virus throughout infection. There has been a recent resurgence of interest in the biology of monocyte subsets and macrophages and their role in HIV pathogenesis, partly fuelled by efforts to understand difficulties in achieving HIV eradication. This article examines the importance of monocyte subsets and tissue macrophages in HIV pathogenesis. Additionally, we will review the role of monocytes and macrophages in the development of serious non-AIDS events including cardiovascular disease and neurocognitive impairment, their significance in viral persistence, and how these cells represent an important obstacle to achieving HIV eradication.

The CD14+CD16+ inflammatory monocyte subset displays increased mitochondrial activity and effector function during acute Plasmodium vivax malaria

Infection with Plasmodium vivax results in strong activation of monocytes, which are important components of both the systemic inflammatory response and parasite control. The overall goal of this study was to define the role of monocytes during P. vivax malaria. Here, we demonstrate that P. vivax-infected patients display significant increase in circulating monocytes, which were defined as CD14(+)CD16- (classical), CD14(+)CD16(+) (inflammatory), and CD14loCD16(+) (patrolling) cells. While the classical and inflammatory monocytes were found to be the primary source of pro-inflammatory cytokines, the CD16(+) cells, in particular the CD14(+)CD16(+) monocytes, expressed the highest levels of activation markers, which included chemokine receptors and adhesion molecules. Morphologically, CD14(+) were distinguished from CD14lo monocytes by displaying larger and more active mitochondria. CD14(+)CD16(+) monocytes were more efficient in phagocytizing P. vivax-infected reticulocytes, which induced them to produce high levels of intracellular TNF-α and reactive oxygen species. Importantly, antibodies specific for ICAM-1, PECAM-1 or LFA-1 efficiently blocked the phagocytosis of infected reticulocytes by monocytes. Hence, our results provide key information on the mechanism by which CD14(+)CD16(+) cells control parasite burden, supporting the hypothesis that they play a role in resistance to P. vivax infection.

Different levels of HIV DNA copy numbers in cerebrospinal fluid cellular subsets

Inequities in the incidence of HIV infection and AIDS with continued persistence of HIV-associated neurocognitive disorders (HAND) exist in populations in Hawaii (HI) and Puerto Rico (PR). We previously reported that peripheral monocyte HIV DNA levels are high in patients in Hawaii with HAND and we now hypothesize that similar findings would be observed in the cerebrospinal fluid (CSF) cellular subsets. Cerebrospinal fluid cells were obtained from patients from PR and HI undergoing neurocognitive testing and sorted into monocytes (CD14+) and lymphocytes (CD14-) and HIV DNA was measured. From six PR subjects (three HAND, three normal cognition, NC) and six HI subjects (three HAND, three NC), HIV DNA burden in CD14+ cells was higher in HAND than NC patients; NC patients had higher HIV DNA burden in CD14-cells versus HAND. Differences in HIV DNA burden in particular CSF cellular subsets suggest that HIV DNA burden may play a role in HAND neuropathogenesis.

Levels of circulating myeloid subpopulations and of heme oxygenase-1 do not predict CD4(+) T cell recovery after the initiation of antiretroviral therapy for HIV disease

The level (or frequency) of circulating monocyte subpopulations such as classical (CD14^hiCD16^-) and non-classical (CD14^dimCD16⁺) monocytes varies during the course of HIV disease progression and antiretroviral therapy (ART). We hypothesized that such variation and/or differences in the degree to which these cells expressed the immunoregulatory enzyme, heme oxygenase-1 (HO-1), would be associated with CD4⁺ T cell recovery after the initiation of ART. This hypothesis was tested in a cross-sectional study of four groups of HIV-infected subjects, including those who were seronegative, untreated virologic controllers [detectable viral load (VL) of <1000 copies/mL], untreated virologic non-controllers [VL > 10,000 copies/mL], and ART-mediated virologic controllers [VL < 75 copies/mL]. A longitudinal analysis of ART-treated subjects was also performed along with regression analysis to determine which biomarkers were associated with and/or predictive of CD4⁺ T cell recovery. Suppressive ART was associated with increased levels of classical monocyte subpopulations (CD14^hiCD16^-) and decreased levels of non-classical monocyte populations (CD14^dimCD16⁺). Among peripheral blood mononuclear cells (PBMCs), HO-1 was found to be most highly up-regulated in CD14⁺ monocytes after ex vivo stimulation. Neither the levels of monocyte subpopulations nor of HO-1 expression in CD14⁺ monocytes were significantly associated with the degree of CD4⁺ T cell recovery. Monocyte subpopulations and HO-1 gene expression were, however, restored to normal levels by suppressive ART. These results suggest that the level of circulating monocyte subpopulations and their expression of HO-1 have no evident relationship to CD4⁺ T cell recovery after the initiation of ART.

Reprint of: Monocyte subsets in man and other species

Monocytes are white blood cells that belong to the mononuclear phagocyte system. They derive from precursors in bone marrow, from there they go into blood, where they have a half-life of 1-2 days, and then they migrate into the various tissues. Monocyte subsets were discovered by means of flow cytometry in human blood some 20 years ago and their phenotype and function has been characterized in detail in health and disease. The subset classification as classical, intermediate and non-classical monocytes appears to apply to other species as well, as reviewed in here by comparing data on human monocytes with the respective cells in the mouse, the rat, the pig, the cow and the horse. The data show that the subsets are homologous between the species but there are important differences in subset-specific gene expression such that findings in a given species cannot be directly translated to man.

CD4 ligation on human blood monocytes triggers macrophage differentiation and enhances HIV infection

A unique aspect of human monocytes, compared to monocytes from many other species, is that they express the CD4 molecule. However, the role of the CD4 molecule in human monocyte development and function is not known. We determined that the activation of CD4 via interaction with major histocompatibility complex class II (MHC-II) triggers cytokine expression and the differentiation of human monocytes into functional mature macrophages. Importantly, we determined that CD4 activation induces intracellular signaling in monocytes and that inhibition of the MAPK and Src family kinase pathways blocked the ability of CD4 ligation to trigger macrophage differentiation. We observed that ligation of CD4 by MHC-II on activated endothelial cells induced CD4-mediated macrophage differentiation of blood monocytes. Finally, CD4 ligation by MHC-II increases the susceptibility of blood-derived monocytes to HIV binding and subsequent infection. Altogether, our studies have identified a novel function for the CD4 molecule on peripheral monocytes and suggest that a unique set of events that lead to innate immune activation differ between humans and mice. Further, these events can have effects on HIV infection and persistence in the macrophage compartment.

IMPORTANCE

The CD4 molecule, as the primary receptor for HIV, plays an important role in HIV pathogenesis. There are many cell types that express CD4 other than the primary HIV target, the CD4(+) T cell. Other than allowing HIV infection, the role of the CD4 molecule on human monocytes or macrophages is not known. We were interested in determining the role of CD4 in human monocyte/macrophage development and function and the potential effects of this on HIV infection. We identified a role for the CD4 molecule in triggering the activation and development of a monocyte into a macrophage following its ligation. Activation of the monocyte through the CD4 molecule in this manner increases the ability of monocytes to bind to and become infected with HIV. Our studies have identified a novel function for the CD4 molecule on peripheral monocytes in triggering macrophage development that has direct consequences for HIV infection.

BAFF and BAFF receptor levels correlate with B cell subset activation and redistribution in controlled human malaria infection

Characteristic features of Plasmodium falciparum malaria are polyclonal B cell activation and an altered composition of the blood B cell compartment, including expansion of CD21(-)CD27(-) atypical memory B cells. BAFF is a key cytokine in B cell homeostasis, but its potential contribution to the modulation of the blood B cell pool during malaria remains elusive. In the controlled human malaria model (CHMI) in malaria-naive Dutch volunteers, we therefore examined the dynamics of BAFF induction and B cell subset activation and composition, to investigate whether these changes are linked to malaria-induced immune activation and, in particular, induction of BAFF. Alterations in B cell composition after CHMI closely resembled those observed in endemic areas. We further found distinct kinetics of proliferation for individual B cell subsets across all developmental stages. Proliferation peaked either immediately after blood-stage infection or at convalescence, and for most subsets was directly associated with the peak parasitemia. Concomitantly, plasma BAFF levels during CHMI were increased and correlated with membrane-expressed BAFF on monocytes and dendritic cells, as well as blood-stage parasitemia and parasite-induced IFN-γ. Correlating with increased plasma BAFF and IFN-γ levels, IgD(-)CD38(low)CD21(-)CD27(-) atypical B cells showed the strongest proliferative response of all memory B cell subsets. This provides unique evidence for a link between malaria-induced immune activation and temporary expansion of this B cell subset. Finally, baseline BAFF-R levels before CHMI were predictive of subsequent changes in proportions of individual B cell subsets. These findings suggest an important role of BAFF in facilitating B cell subset proliferation and redistribution as a consequence of malaria-induced immune activation.

Human classical monocytes control the intracellular stage of Leishmania braziliensis by reactive oxygen species

Leishmania braziliensis are intracellular parasites that cause unique clinical forms of cutaneous leishmaniasis. Previous studies with other leishmania species demonstrated that reactive oxygen species (ROS) control promastigotes, the infective stage of the parasite, but not the amastigote form that exists in the mammalian host. Here we show that ROS inhibits growth of L. braziliensis amastigotes in resting monocytes, and that classical monocytes are primarily responsible for this control. ROS, but not nitric oxide, also contributed to killing of L. braziliensis by IFN-γ activated monocytes. Furthermore, by gene expression profiling of human lesions we found greater expression of genes associated with ROS, but not nitric oxide, compared to normal skin. This study shows that ROS are important for control of L. braziliensis both at the initial stages of infection, as well as at later time points, and highlights that monocyte subsets may play different roles during leishmaniasis.

Monocyte subsets in man and other species

Monocytes are white blood cells that belong to the mononuclear phagocyte system. They derive from precursors in bone marrow, from there they go into blood, where they have a half-life of 1-2 days, and then they migrate into the various tissues. Monocyte subsets were discovered by means of flow cytometry in human blood some 20 years ago and their phenotype and function has been characterized in detail in health and disease. The subset classification as classical, intermediate and non-classical monocytes appears to apply to other species as well, as reviewed in here by comparing data on human monocytes with the respective cells in the mouse, the rat, the pig, the cow and the horse. The data show that the subsets are homologous between the species but there are important differences in subset-specific gene expression such that findings in a given species cannot be directly translated to man.