HIV interactions with monocytes and dendritic cells: viral latency and reservoirs. Retrovirology. 2009;6:51. [PMID: 19486514 PMCID: PMC2697150 DOI: 10.1186/1742-4690-6-51]

HIV-associated bacterial pneumonia

Community-acquired bacterial pneumonia (CAP) remains one of the most common opportunistic infections in patients who are infected with the human immunodeficiency virus (HIV). The risk of CAP increases as the CD4 cell count decreases. The common bacterial pathogens that cause CAP in HIV-infected persons are similar to those in HIV-uninfected individuals, with the pneumococcus being the most common pathogen. Prevention of CAP remains critical and necessitates a comprehensive approach addressing, among many other factors, cigarette smoking cessation strategies, antiretroviral therapy adherence, and immunization against those infections for which effective vaccinations are available.

Dendritic cell-induced activation of latent HIV-1 provirus in actively proliferating primary T lymphocytes

HIV-1 latency remains a formidable barrier towards virus eradication as therapeutic attempts to purge these reservoirs are so far unsuccessful. The pool of transcriptionally silent proviruses is established early in infection and persists for a lifetime, even when viral loads are suppressed below detection levels using anti-retroviral therapy. Upon therapy interruption the reservoir can re-establish systemic infection. Different cellular reservoirs that harbor latent provirus have been described. In this study we demonstrate that HIV-1 can also establish a silent integration in actively proliferating primary T lymphocytes. Co-culturing of these proliferating T lymphocytes with dendritic cells (DCs) activated the provirus from latency. Activation did not involve DC-mediated C-type lectin DC-SIGN signaling or TCR-stimulation but was mediated by DC-secreted component(s) and cell-cell interaction between DC and T lymphocyte that could be inhibited by blocking ICAM-1 dependent adhesion. These results imply that circulating DCs could purge HIV-1 from latency and re-initiate virus replication. Moreover, our data show that viral latency can be established early after infection and supports the idea that actively proliferating T lymphocytes with an effector phenotype contribute to the latent viral reservoir. Unraveling this physiologically relevant purging mechanism could provide useful information for the development of new therapeutic strategies that aim at the eradication of HIV-1 reservoirs.

Cellular and molecular mechanisms involved in the establishment of HIV-1 latency

Latently infected cells represent the major barrier to either a sterilizing or a functional HIV-1 cure. Multiple approaches to reactivation and depletion of the latent reservoir have been attempted clinically, but full depletion of this compartment remains a long-term goal. Compared to the mechanisms involved in the maintenance of HIV-1 latency and the pathways leading to viral reactivation, less is known about the establishment of latent infection. This review focuses on how HIV-1 latency is established at the cellular and molecular levels. We first discuss how latent infection can be established following infection of an activated CD4 T-cell that undergoes a transition to a resting memory state and also how direct infection of a resting CD4 T-cell can lead to latency. Various animal, primary cell, and cell line models also provide insights into this process and are discussed with respect to the routes of infection that result in latency. A number of molecular mechanisms that are active at both transcriptional and post-transcriptional levels have been associated with HIV-1 latency. Many, but not all of these, help to drive the establishment of latent infection, and we review the evidence in favor of or against each mechanism specifically with regard to the establishment of latency. We also discuss the role of immediate silent integration of viral DNA versus silencing of initially active infections. Finally, we discuss potential approaches aimed at limiting the establishment of latent infection.

Recent developments in human immunodeficiency virus-1 latency research

Almost 30 years after its initial discovery, infection with the human immunodeficiency virus-1 (HIV-1) remains incurable and the virus persists due to reservoirs of latently infected CD4(+) memory T-cells and sanctuary sites within the infected individual where drug penetration is poor. Reactivating latent viruses has been a key strategy to completely eliminate the virus from the host, but many difficulties and unanswered questions remain. In this review, the latest developments in HIV-persistence and latency research are presented.

Molecular mechanisms of HIV immune evasion of the innate immune response in myeloid cells

The expression of intrinsic antiviral factors by myeloid cells is a recently recognized mechanism of restricting lentiviral replication. Viruses that enter these cells must develop strategies to evade cellular antiviral factors to establish a productive infection. By studying the cellular targets of virally encoded proteins that are necessary to infect myeloid cells, a better understanding of cellular intrinsic antiviral strategies has now been achieved. Recent findings have provided insight into how the lentiviral accessory proteins, Vpx, Vpr and Vif counteract antiviral factors found in myeloid cells including SAMHD1, APOBEC3G, APOBEC3A, UNG2 and uracil. Here we review our current understanding of the molecular basis of how cellular antiviral factors function and the viral countermeasures that antagonize them to promote viral transmission and spread.

SAMHD1 restricts HIV-1 infection in dendritic cells (DCs) by dNTP depletion, but its expression in DCs and primary CD4+ T-lymphocytes cannot be upregulated by interferons

Background

SAMHD1 is an HIV-1 restriction factor in non-dividing monocytes, dendritic cells (DCs), macrophages, and resting CD4⁺ T-cells. Acting as a deoxynucleoside triphosphate (dNTP) triphosphohydrolase, SAMHD1 hydrolyzes dNTPs and restricts HIV-1 infection in macrophages and resting CD4⁺ T-cells by decreasing the intracellular dNTP pool. However, the intracellular dNTP pool in DCs and its regulation by SAMHD1 remain unclear. SAMHD1 has been reported as a type I interferon (IFN)-inducible protein, but whether type I IFNs upregulate SAMHD1 expression in primary DCs and CD4⁺ T-lymphocytes is unknown.

Results

Here, we report that SAMHD1 significantly blocked single-cycle and replication-competent HIV-1 infection of DCs by decreasing the intracellular dNTP pool and thereby limiting the accumulation of HIV-1 late reverse transcription products. Type I IFN treatment did not upregulate endogenous SAMHD1 expression in primary DCs or CD4⁺ T-lymphocytes, but did in HEK 293T and HeLa cell lines. When SAMHD1 was over-expressed in these two cell lines to achieve higher levels than that in DCs, no HIV-1 restriction was observed despite partially reducing the intracellular dNTP pool.

Conclusions

Our results suggest that SAMHD1-mediated reduction of the intracellular dNTP pool in DCs is a common mechanism of HIV-1 restriction in myeloid cells. Endogenous expression of SAMHD1 in primary DCs or CD4⁺ T-lymphocytes is not upregulated by type I IFNs.

Macrophages and their relevance in Human Immunodeficiency Virus Type I infection

Macrophages are important target cells for the Human Immunodeficiency Virus Type I (HIV-1) in vivo. Several studies have assessed the molecular biology of the virus in this cell type, and a number of differences towards HIV-1 infection of CD4+ T cells have been described. There is a broad consensus that macrophages resist HIV-1 infection much better than CD4+ T cells. Among other reasons, this is due to the presence of the recently identified host cell restriction factor SamHD1, which is strongly expressed in cells of the myeloid lineage. Furthermore, macrophages produce and release relatively low amounts of infectious HIV-1 and are less sensitive to viral cytotoxicity in comparison to CD4+ T cells. Nevertheless, macrophages play a crucial role in the different phases of HIV-1 infection. In this review, we summarize and discuss the significance of macrophages for HIV-1 transmission, the acute and chronic phases of HIV-1 infection, the development of acquired immunodeficiency syndrome (AIDS) and HIV-associated diseases, including neurocognitive disorders. We propose that interaction of HIV-1 with macrophages is crucial during all stages of HIV-1 infection. Thus, long-term successful treatment of HIV-1 infected individuals requires potent strategies to prevent HIV-1 from entering and persisting in these cells.

HIV-1 induces telomerase activity in monocyte-derived macrophages, possibly safeguarding one of its reservoirs

Monocyte-derived macrophages (MDM) are widely distributed in all tissues and organs, including the central nervous system, where they represent the main part of HIV-infected cells. In contrast to activated CD4(+) T lymphocytes, MDM are resistant to cytopathic effects and survive HIV infection for a long period of time. The molecular mechanisms of how HIV is able to persist in macrophages are not fully elucidated yet. In this context, we have studied the effect of in vitro HIV-1 infection on telomerase activity (TA), telomere length, and DNA damage. Infection resulted in a significant induction of TA. This increase was directly proportional to the efficacy of HIV infection and was found in both nuclear and cytoplasmic extracts, while neither UV light-inactivated HIV nor exogenous addition of the viral protein Tat or gp120 affected TA. Furthermore, TA was not modified during monocyte-macrophage differentiation, MDM activation, or infection with vaccinia virus. HIV infection did not affect telomere length. However, HIV-infected MDM showed less DNA damage after oxidative stress than noninfected MDM, and this resistance was also increased by overexpressing telomerase alone. Taken together, our results suggest that HIV induces TA in MDM and that this induction might contribute to cellular protection against oxidative stress, which could be considered a viral strategy to make macrophages better suited as longer-lived, more resistant viral reservoirs. In the light of the clinical development of telomerase inhibitors as anticancer therapeutics, inhibition of TA in HIV-infected macrophages might also represent a novel therapeutic target against viral reservoirs.

Modulation of HIV reservoirs by host HLA: bridging the gap between vaccine and cure

Latent HIV reservoirs are the greatest challenge facing an HIV cure. Here, we review recent evidence supporting an important role for the host immune response, in particular HLA class I-restricted CD8+ T lymphocytes, in modulating HIV reservoirs during natural infection. These observations indicate that factors governing immune-mediated control of HIV may also contribute to the clearance of viral reservoirs. As such, critical gaps in our understanding of HIV immunology hinder efforts to develop both an effective HIV vaccine as well as novel therapies that may lead to a cure. The importance of elucidating correlates of protective cellular immunity should be recognized during research to develop and test potential HIV elimination strategies.

MicroRNA-mediated restriction of HIV-1 in resting CD4+ T cells and monocytes

In contrast to activated CD4⁺ T cells and differentiated macrophages, resting CD4⁺ T cells and monocytes are non-permissive for HIV-1 replication. The mediators which regulate the resting or quiescent phenotype are often actively involved in the restriction of viral replication and the establishment and maintenance of viral latency. Recently, certain microRNAs which are highly expressed in resting cells have been implicated in this capacity, inhibiting the expression of cellular proteins that are also viral co-factors; following activation these microRNAs exhibit decreased expression, while their targets are correspondingly up-regulated, contributing to a favorable milieu for virus replication. Other microRNAs exhibiting a similar expression pattern in resting and activated cells have been shown to directly target the HIV-1 genome. In this review we will discuss the resting state and the causes behind viral restriction in resting cells, with emphasis on the role of microRNAs.

Translation of Pur-α is targeted by cellular miRNAs to modulate the differentiation-dependent susceptibility of monocytes to HIV-1 infection

The postentry restriction of HIV-1 replication in monocytes can be relieved when they differentiate to dendritic cells (DCs) or macrophages. Multiple mechanisms have been proposed to interpret the differentiation-dependent susceptibility of monocytes to HIV-1 infection, and the absence of host-cell-encoded essential factors for HIV-1 completing the life cycle may provide an explanation. We have analyzed the gene expression profile in monocytes by mRNA microarray and compared it with that of differentiated DCs. We demonstrated that purine-rich element binding protein α (Pur-α), a host-cell-encoded ubiquitous, sequence-specific DNA- and RNA-binding protein, showed inadequate expression in monocytes, and the translation of Pur-α mRNA was repressed by cell-expressed microRNA (miRNA). These Pur-α-targeted miRNAs modulated the differentiation-dependent susceptibility of monocytes/DCs to HIV-1 infection, because rescue of Pur-α expression by transfection of miRNA inhibitors relieved the restriction of HIV-1 infection in monocytes, and ectopic input of miRNA mimics significantly reduced HIV-1 infection of monocyte-derived DCs (MDDCs). Collectively, our data emphasized that inadequate host factors contribute to HIV-1 restriction in monocytes, and cellular miRNAs modulate differentiation-dependent susceptibility of host cells to HIV-1 infection. Elaboration of HIV-1 restriction in host cells facilitates our understanding of viral pathogenesis and the search for a new antiviral strategy.

HIV-1 infection and first line ART induced differential responses in mitochondria from blood lymphocytes and monocytes: the ANRS EP45 "Aging" study

BACKGROUND

The ANRS EP45 "Aging" study investigates the cellular mechanisms involved in the accelerated aging of HIV-1 infected and treated patients. The data reported focus on mitochondria, organelles known to be involved in cell senescence.

METHODS

49 HIV-1 infected patients untreated with antiretroviral therapy, together with 49 seronegative age- and sex-matched control subjects and 81 HIV-1 infected and treated patients, were recruited by 3 AIDS centres (Marseille, Montpellier, Nice; France; http://clinicaltrials.gov/, NCT01038999). In more than 88% of treated patients, the viral load was <40 copies/ml and the CD4+ cell count was >500/mm(3). ROS (reactive oxygen species) production and ΔΨm (inner membrane potential) were measured by flow cytometry in blood lymphocytes and monocytes (functional parameters). Three mitochondrial network quantitative morphological parameters were computed using confocal microscopy and image analysis. Three PBMC mitochondrial proteins (porin and subunits 2 and 4 of cytochrome C oxidase encoded by mtDNA or nuclear DNA, respectively) were analysed by western blotting.

RESULTS

Quantitative changes in PBMC mitochondrial proteins were not induced by either HIV-1 infection or ART. Discriminant analysis integrating functional (ROS production and ΔΨm) or morphological (network volume density, fragmentation and branching) parameters revealed HIV-1 infection and ART differential effects according to cell type. First line ART tended to rescue lymphocyte mitochondrial parameters altered by viral infection, but induced slight changes in monocytes. No statistical difference was found between the effects of three ART regimens on mitochondrial parameters. Correlations between functional parameters and viral load confirmed the damaging effects of HIV-1 in lymphocyte mitochondria.

CONCLUSIONS

In patients considered to be clinically stable, mitochondria exhibited functional and morphological modifications in PBMCs resulting from either direct or indirect effects of HIV-1 infection (lymphocytes), or from first line ART (monocytes). Together with other tissue impairments, these changes may contribute to global aging.

Mycobacteria-infected bystander macrophages trigger maturation of dendritic cells and enhance their ability to mediate HIV transinfection

Synergistic interplay between Mycobacterium tuberculosis (Mtb) and HIV in coinfected individuals leads to the acceleration of both tuberculosis and HIV disease. Mtb, as well as HIV, may modulate the function of many immune cells, including DCs. To dissect the bystander impact of Mφs infected with Mtb on DC functionality, we here investigated changes in DC phenotype, cytokine profiles, and HIV-1 transinfecting ability. An in vitro system was used in which human monocyte-derived DCs were exposed to soluble factors released by Mφs infected with mycobacteria, including virulent clinical Mtb isolates and nonvirulent BCG. Soluble factors secreted from Mtb-infected Mφs, and to a lesser extent BCG-infected Mφs, resulted in the production of proinflammatory cytokines and partial upregulation of DC maturation markers. Interestingly, the HIV-1 transinfecting ability of DCs was enhanced upon exposure to soluble factors released by Mtb-infected Mφs. In summary, our study shows that DCs exposed to soluble factors released by mycobacteria-infected Mφs undergo maturation and display an augmented ability to transmit HIV-1 in trans. These findings highlight the important role of bystander effects during the course of Mtb-HIV coinfection and suggest that Mtb-infected Mφs may contribute to an environment that supports DC-mediated spread and amplification of HIV in coinfected individuals.

HIV type 1 genetic variation in foreskin and blood from subjects in Rakai, Uganda

The foreskin contains a subset of dendritic cells, macrophages, and CD4(+) and CD8(+) T cells that may be targets for initial HIV infection in female-to-male sexual transmission of HIV-1. We present analyses comparing HIV-1 sequences isolated from foreskin DNA and serum RNA in 12 heterosexual men enrolled in an adult male circumcision trial performed in Rakai, Uganda. Phylogenetic analysis demonstrated three topologies: (1) little divergence between foreskin and serum, (2) multiple genetic bottlenecks occurring in both foreskin and serum, and (3) complete separation of foreskin and serum populations. The latter tree topology provided evidence that foreskin may serve as a reservoir for distinct HIV-1 strains. Distance and recombination analysis also demonstrated that viral genotypes in the foreskin might segregate independently from the circulating pool of viruses.

HIV-1 Gag-virus-like particles inhibit HIV-1 replication in dendritic cells and T cells through IFN-α-dependent upregulation of APOBEC3G and 3F

Human immunodeficiency virus-1 (HIV-1) infection and the acquired immune deficiency syndrome (AIDS) pandemic remain global threats in the absence of a protective or a therapeutic vaccine. HIV-1 replication is reportedly inhibited by some cellular factors, including APOBEC3G (A3G) and APOBEC3F (A3F), which are well known inhibitors of HIV-1. Recently, HIV-1 Gag-virus-like particles (Gag-VLPs) have been shown to be safe and potent HIV-1 vaccine candidates that can elicit strong cellular and humoral immunity without need of any adjuvant. In this report, we stimulated human monocyte-derived dendritic cells (DCs) with Gag-VLPs and we demonstrated that Gag-VLP-treated DCs (VLP-DCs) produced interferon alpha (IFN-α), along with an increase in mRNA and protein expression of A3G and A3F. Gag-VLPs inhibited HIV-1 replication not only in DCs themselves, but also in cocultured T cells in an IFN-α-dependent manner. In addition, A3G/3F content in HIV virions released from VLP-DCs increased. Both the increase in A3G/3F expression and the inhibition of HIV-1 replication were reversed by anti-IFN-α or anti-IFNAR antibodies. Our findings in this study provide insight into the mechanism of Gag-VLP-induced inhibition of HIV-1 replication in DCs and T cells.

Macroautophagy Regulation during HIV-1 Infection of CD4+ T Cells and Macrophages

Autophagy is an intracellular mechanism whereby pathogens, particularly viruses, are destroyed in autolysosomes after their entry into targets cells. Therefore, to survive and replicate in host cells, viruses have developed multiple strategies to either counteract or exploit this process. The aim of this review is to outline the known relationships between HIV-1 and autophagy in CD4+ T lymphocytes and macrophages, two main HIV-1 cell targets. The differential regulation of autophagy in these two cell-types is highlighted and its potential consequences in terms of viral replication and physiopathology discussed.

Differential effects of Vpr on single-cycle and spreading HIV-1 infections in CD4+ T-cells and dendritic cells

The Vpr protein of human immunodeficiency virus type 1 (HIV-1) contributes to viral replication in non-dividing cells, specifically those of the myeloid lineage. However, the effects of Vpr in enhancing HIV-1 infection in dendritic cells have not been extensively investigated. Here, we evaluated the role of Vpr during infection of highly permissive peripheral blood mononuclear cells (PBMCs) and CD4(+) T-cells and compared it to that of monocyte-derived dendritic cells (MDDCs), which are less susceptible to HIV-1 infection. Infections of dividing PBMCs and non-dividing MDDCs were carried out with single-cycle and replication-competent HIV-1 encoding intact Vpr or Vpr-defective mutants. In contrast to previous findings, we observed that single-cycle HIV-1 infection of both PBMCs and MDDCs was significantly enhanced in the presence of Vpr when the viral stocks were carefully characterized and titrated. HIV-1 DNA quantification revealed that Vpr only enhanced the reverse transcription and nuclear import processes in single-cycle HIV-1 infected MDDCs, but not in CD4(+) T-cells. However, a significant enhancement in HIV-1 gag mRNA expression was observed in both CD4(+) T-cells and MDDCs in the presence of Vpr. Furthermore, Vpr complementation into HIV-1 virions did not affect single-cycle viral infection of MDDCs, suggesting that newly synthesized Vpr plays a significant role to facilitate single-cycle HIV-1 infection. Over the course of a spreading infection, Vpr significantly enhanced replication-competent HIV-1 infection in MDDCs, while it modestly promoted viral infection in activated PBMCs. Quantification of viral DNA in replication-competent HIV-1 infected PBMCs and MDDCs revealed similar levels of reverse transcription products, but increased nuclear import in the presence of Vpr independent of the cell types. Taken together, our results suggest that Vpr has differential effects on single-cycle and spreading HIV-1 infections, which are dependent on the permissiveness of the target cell.

Achieving a cure for HIV infection: do we have reasons to be optimistic?

The introduction of highly active antiretroviral therapy (HAART) in 1996 has transformed a lethal disease to a chronic pathology with a dramatic decrease in mortality and morbidity of AIDS-related symptoms in infected patients. However, HAART has not allowed the cure of HIV infection, the main obstacle to HIV eradication being the existence of quiescent reservoirs. Several other problems have been encountered with HAART (such as side effects, adherence to medication, emergence of resistance and cost of treatment), and these motivate the search for new ways to treat these patients. Recent advances hold promise for the ultimate cure of HIV infection, which is the topic of this review. Besides these new strategies aiming to eliminate the virus, efforts must be made to improve current HAART. We believe that the cure of HIV infection will not be attained in the short term and that a strategy based on purging the reservoirs has to be associated with an aggressive HAART strategy.

Ethanol-mediated regulation of cytochrome P450 2A6 expression in monocytes: role of oxidative stress-mediated PKC/MEK/Nrf2 pathway

Cytochrome P450 2A6 (CYP2A6) is known to metabolize nicotine, the major constituent of tobacco, leading to the production of toxic metabolites and induction of oxidative stress that result in liver damage and lung cancer. Recently, we have shown that CYP2A6 is induced by ethanol and metabolizes nicotine into cotinine and other metabolites leading to generation of reactive oxygen species (ROS) in U937 monocytes. However, the mechanism by which CYP2A6 is induced by ethanol is unknown. In this study, we have examined the role of the PKC/Nrf2 pathway (protein kinase C-mediated phosphorylation and translocation of nuclear erythroid 2-related factor 2 to the nucleus) in ethanol-mediated CYP2A6 induction. Our results showed that 100 mM ethanol significantly induced CYP2A6 mRNA and protein (~150%) and increased ROS formation, and induction of gene expression and ROS were both completely blocked by treatment with either a CYP2E1 inhibitor (diallyl sulfide) or an antioxidant (vitamin C). The results suggest the role of oxidative stress in the regulation of CYP2A6 expression. Subsequently, we investigated the role of Nrf2 pathway in oxidative stress-mediated regulation of CYP2A6 expression in U937 monocytes. Our results showed that butylated hydroxyanisole, a stabilizer of nuclear Nrf2, increased CYP2A6 levels >200%. Staurosporine, an inhibitor of PKC, completely abolished ethanol-induced CYP2A6 expression. Furthermore, our results showed that a specific inhibitor of mitogen-activated protein kinase kinase (MEK) (U0126) completely abolished ethanol-mediated CYP2A6 induction and Nrf2 translocation. Overall, these results suggest that CYP2E1-mediated oxidative stress produced as a result of ethanol metabolism translocates Nrf2 into the nucleus through PKC/MEK pathway, resulting in the induction of CYP2A6 in monocytes. An increased level of CYP2A6 in monocytes is expected to further increase oxidative stress in smokers through CYP2A6-mediated nicotine metabolism. Thus, this study has clinical relevance because of the high incidence of alcohol use among smokers, especially in HIV-infected individuals.

Regulation of Mycobacterium tuberculosis-dependent HIV-1 transcription reveals a new role for NFAT5 in the toll-like receptor pathway

Tuberculosis (TB) disease in HIV co-infected patients contributes to increased mortality by activating innate and adaptive immune signaling cascades that stimulate HIV-1 replication, leading to an increase in viral load. Here, we demonstrate that silencing of the expression of the transcription factor nuclear factor of activated T cells 5 (NFAT5) by RNA interference (RNAi) inhibits Mycobacterium tuberculosis (MTb)-stimulated HIV-1 replication in co-infected macrophages. We show that NFAT5 gene and protein expression are strongly induced by MTb, which is a Toll-like receptor (TLR) ligand, and that an intact NFAT5 binding site in the viral promoter of R5-tropic HIV-1 subtype B and subtype C molecular clones is required for efficent induction of HIV-1 replication by MTb. Furthermore, silencing by RNAi of key components of the TLR pathway in human monocytes, including the downstream signaling molecules MyD88, IRAK1, and TRAF6, significantly inhibits MTb-induced NFAT5 gene expression. Thus, the innate immune response to MTb infection induces NFAT5 gene and protein expression, and NFAT5 plays a crucial role in MTb regulation of HIV-1 replication via a direct interaction with the viral promoter. These findings also demonstrate a general role for NFAT5 in TLR- and MTb-mediated control of gene expression.

The major cause of AIDS deaths globally has been tuberculosis (TB), which is caused by the bacterium Mycobacterium tuberculosis (MTb). Co-infection with MTb exacerbates human immunodeficiency virus type1 (HIV-1) replication and disease progression via both innate and adaptive host immune responses to MTb infection. In this report, we present evidence that the transcription factor NFAT5 plays a crucial role in MTb-induced HIV-1 replication in human peripheral blood cells and monocytes. We also show that MTb infection itself stimulates NFAT5 gene expression in human monocytes and that its expression involves the TLR signalling pathway and requires the downstream adaptor proteins MyD88, IRAK1, and TRAF6. This identification of a novel role for NFAT5 in TB/HIV-1 co-infection reveals that NFAT5 is a major mediator of TLR-dependent gene expression and thus provides a potential new therapeutic target for treatment of HIV-1 and possibly other diseases.

Molecular Understanding of HIV-1 Latency

The introduction of highly active antiretroviral therapy (HAART) has been an important breakthrough in the treatment of HIV-1 infection and has also a powerful tool to upset the equilibrium of viral production and HIV-1 pathogenesis. Despite the advent of potent combinations of this therapy, the long-lived HIV-1 reservoirs like cells from monocyte-macrophage lineage and resting memory CD4+ T cells which are established early during primary infection constitute a major obstacle to virus eradication. Further HAART interruption leads to immediate rebound viremia from latent reservoirs. This paper focuses on the essentials of the molecular mechanisms for the establishment of HIV-1 latency with special concern to present and future possible treatment strategies to completely purge and target viral persistence in the reservoirs.

HIV-1 Nef enhances dendritic cell-mediated viral transmission to CD4+ T cells and promotes T-cell activation

HIV-1 Nef enhances dendritic cell (DC)-mediated viral transmission to CD4(+) T cells, but the underlying mechanism is not fully understood. It is also unknown whether HIV-1 infected DCs play a role in activating CD4(+) T cells and enhancing DC-mediated viral transmission. Here we investigated the role of HIV-1 Nef in DC-mediated viral transmission and HIV-1 infection of primary CD4(+) T cells using wild-type HIV-1 and Nef-mutated viruses. We show that HIV-1 Nef facilitated DC-mediated viral transmission to activated CD4(+) T cells. HIV-1 expressing wild-type Nef enhanced the activation and proliferation of primary resting CD4(+) T cells. However, when co-cultured with HIV-1-infected autologous DCs, there was no significant trend for infection- or Nef-dependent proliferation of resting CD4(+) T cells. Our results suggest an important role of Nef in DC-mediated transmission of HIV-1 to activated CD4(+) T cells and in the activation and proliferation of resting CD4(+) T cells, which likely contribute to viral pathogenesis.

Pattern Recognition Receptors in HIV Transmission

Dendritic cells (DCs), Langerhans cells (LCs), and macrophages are innate immune cells that reside in genital and intestinal mucosal tissues susceptible to HIV-1 infection. These innate cells play distinct roles in initiation of HIV-1 infection and induction of anti-viral immunity. DCs are potent migratory cells that capture HIV-1 and transfer virus to CD4⁺ T cells in the lymph nodes, whereas LCs have a protective anti-viral function, and macrophages function as viral reservoirs since they produce viruses over prolonged times. These differences are due to the different immune functions of these cells partly dependent on the expression of specific pattern recognition receptors. Expression of Toll-like receptors, C-type lectin receptors, and cell-specific machinery for antigen uptake and processing strongly influence the outcome of virus interactions.

Proline-proline-glutamic acid (PPE) protein Rv1168c of Mycobacterium tuberculosis augments transcription from HIV-1 long terminal repeat promoter

Cells of the monocyte/macrophage lineage are shown to play a role in the pathogenesis of human immunodeficiency virus (HIV). The occurrence of HIV type 1 (HIV-1) infection is found to be accelerated in people infected with Mycobacterium tuberculosis, but the mechanism by which mycobacterial protein(s) induces HIV-1 LTR trans-activation is not clearly understood. We show here that the M. tuberculosis proline-proline-glutamic acid (PPE) protein Rv1168c (PPE17) can augment transcription from HIV-1 LTR in monocyte/macrophage cells. Rv1168c interacts specifically with Toll-like receptor-2 (TLR2) resulting in downstream activation of nuclear factor-κB (NF-κB) resulting in HIV-1 LTR trans-activation. Another PPE protein, Rv1196 (PPE18), was also found to interact with TLR2 but had no effect on HIV-1 LTR trans-activation because of its inability to activate the NF-κB signaling pathway. In silico docking analyses and mutation experiments have revealed that the N-terminal domain of Rv1168c specifically interacts with LRR motifs 15-20 of TLR2, and this site of interaction is different from that of Rv1196 protein (LRR motifs 11-15), indicating that the site of interaction on TLR2 dictates the downstream signaling events leading to activation of NF-κB. This information may help in understanding the mechanism of pathogenesis of HIV-1 during M. tuberculosis co-infection.

Deployment of the human immunodeficiency virus type 1 protein arsenal: combating the host to enhance viral transcription and providing targets for therapeutic development

Despite the success of highly active antiretroviral therapy in combating human immunodeficiency virus type 1 (HIV-1) infection, the virus still persists in viral reservoirs, often in a state of transcriptional silence. This review focuses on the HIV-1 protein and regulatory machinery and how expanding knowledge of the function of individual HIV-1-coded proteins has provided valuable insights into understanding HIV transcriptional regulation in selected susceptible cell types. Historically, Tat has been the most studied primary transactivator protein, but emerging knowledge of HIV-1 transcriptional regulation in cells of the monocyte-macrophage lineage has more recently established that a number of the HIV-1 accessory proteins like Vpr may directly or indirectly regulate the transcriptional process. The viral proteins Nef and matrix play important roles in modulating the cellular activation pathways to facilitate viral replication. These observations highlight the cross talk between the HIV-1 transcriptional machinery and cellular activation pathways. The review also discusses the proposed transcriptional regulation mechanisms that intersect with the pathways regulated by microRNAs and how development of the knowledge of chromatin biology has enhanced our understanding of key protein-protein and protein-DNA interactions that form the HIV-1 transcriptome. Finally, we discuss the potential pharmacological approaches to target viral persistence and enhance effective transcription to purge the virus in cellular reservoirs, especially within the central nervous system, and the novel therapeutics that are currently in various stages of development to achieve a much superior prognosis for the HIV-1-infected population.

Minocycline modulates antigen-specific CTL activity through inactivation of mononuclear phagocytes in patients with HTLV-I associated neurologic disease

BACKGROUND

The activation of mononuclear phagocytes (MPs), including monocytes, macrophages and dendritic cells, contributes to central nervous system inflammation in various neurological diseases. In HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), MPs are reservoirs of HTLV-I, and induce proinflammatory cytokines and excess T cell responses. The virus-infected or activated MPs may play a role in immuneregulation and disease progression in patients with HTLV-I-associated neurological diseases.

RESULTS

Phenotypic analysis of CD14⁺ monocytes in HAM/TSP patients demonstrated high expression of CX3CR1 and HLA-DR in CD14lowCD16⁺ monocytes, compared to healthy normal donors (NDs) and asymptomatic carriers (ACs), and the production of TNF-α and IL-1β in cultured CD14⁺ cells of HAM/TSP patients. CD14⁺ cells of HAM/TSP patients also showed acceleration of HTLV-I Tax expression in CD4⁺ T cells. Minocycline, an inhibitor of activated MPs, decreased TNF-α expression in CD14⁺ cells and IL-1β release in PBMCs of HAM/TSP patients. Minocycline significantly inhibited spontaneous lymphoproliferation and degranulation/IFN-γ expression in CD8⁺ T cells of HAM/TSP patients. Treatment of minocycline also inhibited IFN-γ expression in CD8⁺ T cells of HAM/TSP patients after Tax11-19 stimulation and downregulated MHC class I expression in CD14⁺ cells.

CONCLUSION

These results demonstrate that minocycline directly inhibits the activated MPs and that the downregulation of MP function can modulate CD8⁺ T cells function in HAM/TSP patients. It is suggested that activated MPs may be a therapeutic target for clinical intervention in HAM/TSP.

Evolutionary and functional analyses of the interaction between the myeloid restriction factor SAMHD1 and the lentiviral Vpx protein

SAMHD1 has recently been identified as an HIV-1 restriction factor operating in myeloid cells. As a countermeasure, the Vpx accessory protein from HIV-2 and certain lineages of SIV have evolved to antagonize SAMHD1 by inducing its ubiquitin-proteasome-dependent degradation. Here, we show that SAMHD1 experienced strong positive selection episodes during primate evolution that occurred in the Catarrhini ancestral branch prior to the separation between hominoids (gibbons and great apes) and Old World monkeys. The identification of SAMHD1 residues under positive selection led to mapping the Vpx-interaction domain of SAMHD1 to its C-terminal region. Importantly, we found that while SAMHD1 restriction activity toward HIV-1 is evolutionarily maintained, antagonism of SAMHD1 by Vpx is species-specific. The distinct evolutionary signature of SAMHD1 sheds light on the development of its antiviral specificity.

Monocyte maturation, HIV susceptibility, and transmigration across the blood brain barrier are critical in HIV neuropathogenesis

HIV continues to be a global health crisis with more than 34 million people infected worldwide (UNAIDS: Report on the Global AIDS Epidemic 2010, Geneva, World Health Organization). HIV enters the CNS within 2 weeks of infection and establishes a spectrum of HAND in a large percentage of infected individuals. These neurologic deficits greatly impact the quality of life of those infected with HIV. The establishment of HAND is largely attributed to monocyte transmigration, particularly that of a mature CD14(+)CD16(+) monocyte population, which is more susceptible to HIV infection, across the BBB into the CNS parenchyma in response to chemotactic signals. To enter the CNS, junctional proteins on the monocytes must participate in homo- and heterotypic interactions with those present on BMVECs of the BBB as they transmigrate across the barrier. This transmigration is responsible for bringing virus into the brain and establishing chronic neuroinflammation. While there is baseline trafficking of monocytes into the CNS, the increased chemotactic signals present during HIV infection of the brain promote exuberant monocyte transmigration into the CNS. This review will discuss the mechanisms of monocyte differentiation/maturation, HIV infectivity, and transmigration into the CNS parenchyma that contribute to the establishment of cognitive impairment in HIV-infected individuals. It will focus on markers of monocyte subpopulations, how differentiation/maturation alters HIV infectivity, and the mechanisms that promote their increased transmigration across the BBB into the CNS.

Cellular and viral mechanisms of HIV-1 transmission mediated by dendritic cells

Dendritic cells (DCs) play a key role in the initial infection and cell-to-cell transmission events that occur upon HIV-1 infection. DCs interact closely with CD4(+) T cells, the main target of HIV-1 replication. HIV-1 challenged DCs and target CD4(+) T cells form a virological synapse that allows highly efficient transmission of HIV-1 to the target CD4(+) T cells, in the absence of productive HIV-1 replication in the DCs. Immature and subsets of mature DCs show distinct patterns of HIV-1 replication and cell-to-cell transmission, depending upon the maturation stimulus that is used. The cellular and viral mechanisms that promote formation of the virological synapse have been the subject of intense study and the most recent progress is discussed here. Characterizing the cellular and viral factors that affect DC-mediated cell-to-cell transmission of HIV-1 to CD4(+) T cells is vitally important to understanding, and potentially blocking, the initial dissemination of HIV-1 in vivo.

Epigenomic deregulation in the immune system

Proper immune function is the result of multiple cell commitment and differentiation steps, and adequate control of activation mechanisms. Deregulation of transcriptional programs in immune cells leads to the development of hematological malignancies, autoimmune diseases or immunodeficiencies. In this sense, epigenetic control of gene expression plays an essential role in the correct function of the immune system and the integrity of identity of relevant cell types. Epigenetic deregulation can result as a consequence of genetic changes in transcription factors, elements of signaling pathways or epigenetic enzymes, or as an effect of a variety of environmental factors. On top of genetic predisposition, viral infection and other external factors influence the development of immune-related diseases. In recent years, major strides have been made towards understanding the contribution of genetics in these immune disorders. Less progress has been made in dissecting the contribution of epigenetic factors in their etiology. Herein, it is presented what is currently known about epigenetic alterations in immune system associated disorders. It is also discussed how epigenomic analysis can help to understand the molecular basis of these diseases and how this information can be used in the clinical setting.

In vitro effect of anti-human immunodeficiency virus CCR5 antagonist maraviroc on chemotactic activity of monocytes, macrophages and dendritic cells

Compounds targeting the chemokine receptor CCR5 have recently been approved for treatment of human immunodeficiency virus (HIV) infection. Given the central role of CCR5 in inflammation and recruitment of antigen-presenting cells (APC), it is important to investigate the immunological consequences of pharmacological inhibition of CCR5. We evaluated the in vitro effect of different concentrations of CCR5 antagonist maraviroc (MVC) on cell migration of monocytes, macrophages (MO) and monocyte-derived dendritic cells (MDC) towards peptide formyl-methionyl-leucyl-phenylalanine (fMLP) and chemokines regulated upon activation normal T cell expressed and secreted (RANTES) and CCL4/macrophage inflammatory protein-1 (MIP-1β) and CCL2/monocyte chemotactic protein-1 (MCP-1). Results of flow cytometric analysis showed that monocytes treated in vitro with MVC exhibited a significant dose-dependent reduction of chemotaxis towards MIP-1β and MCP-1. fMLP-induced chemotactic activity decreased only at higher concentration (1 µM and 10 µM of MVC). In addition, all concentrations of MVC (0·1, 1 and 10 µM) induced in vitro a significant inhibition of chemotaxis of MO and MDC in response to all tested chemoattractants. No change in phenotype (CD1a and CD14) and CCR1, CCR4, CCR5 and formyl peptide receptor (FPR) expression was seen after in vitro treatment with MVC. These findings suggest that CCR5 antagonist MVC may have the in vitro ability of inhibiting the migration of innate immune cells by mechanism which could be independent from the pure anti-HIV effect. The drug might have a potential role in the down-regulation of HIV-associated chronic inflammation by blocking the recirculation and trafficking of MO and MDC.

Penicillium marneffei-stimulated dendritic cells enhance HIV-1 trans-infection and promote viral infection by activating primary CD4+ T cells

Penicillium marneffei (P. marneffei) is considered an indicator pathogen of AIDS, and the endemicity and clinical features of P. marneffei have been described. While, how the co-infection of P. marneffei exacerbate deterioration of the immune response remains poorly understood. Here we isolated P. marneffei from the cutaneous lesions of AIDS patients and analyzed its effects on HIV-1-dendritic cells (DCs) interaction. We demonstrated that the monocyte-derived dendritic cells (MDDCs) could be activated by both thermally dimorphic forms of P. marneffei for significantly promoting HIV-1 trans-infection of CD4⁺ T cells, while these activated MDDCs were refractory to HIV-1 infection. Mechanistically, P. marneffei-activated MDDCs endocytosed large amounts of HIV-1 and sequestrated the internalized viruses into tetrapasnin CD81⁺ compartments potentially for proteolysis escaping. The activated MDDCs increased expression of intercellular adhesion molecule 1 and facilitated the formation of DC-T-cell conjunctions, where much more viruses were recruited. Moreover, we found that P. marneffei-stimulated MDDCs efficiently activated resting CD4⁺ T cells and induced more susceptible targets for viral infection. Our findings demonstrate that DC function and its interaction with HIV-1 have been modulated by opportunistic pathogens such as P. marneffei for viral dissemination and infection amplification, highlighting the importance of understanding DC-HIV-1 interaction for viral immunopathogenesis elucidation.

Viral determinants of HIV-1 macrophage tropism

Macrophages are important target cells for HIV-1 infection that play significant roles in the maintenance of viral reservoirs and other aspects of pathogenesis. Understanding the determinants of HIV-1 tropism for macrophages will inform HIV-1 control and eradication strategies. Tropism for macrophages is both qualitative (infection or not) and quantitative (replication capacity). For example many R5 HIV-1 isolates cannot infect macrophages, but for those that can the macrophage replication capacity can vary by up to 1000-fold. Some X4 viruses are also capable of replication in macrophages, indicating that cellular tropism is partially independent of co-receptor preference. Preliminary data obtained with a small number of transmitted/founder viruses indicate inefficient macrophage infection, whereas isolates from later in disease are more frequently tropic for macrophages. Thus tropism may evolve over time, and more macrophage tropic viruses may be implicated in the pathogenesis of advanced HIV-1 infection. Compartmentalization of macrophage-tropic brain-derived envelope glycoproteins (Envs), and non-macrophage tropic non-neural tissue-derived Envs points to adaptation of HIV-1 quasi-species in distinct tissue microenvironments. Mutations within and adjacent to the Env-CD4 binding site have been identified that determine macrophage tropism at the entry level, but post-entry molecular determinants of macrophage replication capacity involving HIV-1 accessory proteins need further definition.

Role of p53 in neurodegenerative diseases

BACKGROUND

p53 plays an important role in many areas of cellular physiology and biology, ranging from cellular development and differentiation to cell cycle arrest and apoptosis. Many of its functions are attributed to its role in assuring proper cellular division. However, since the establishment of its role in cell cycle arrest, damage repair, and apoptosis (thus also establishing its importance in cancer development), numerous reports have demonstrated additional functions of p53 in various cells. In particular, p53 appears to have important functions as it relates to neurodegeneration and synaptic plasticity.

OBJECTIVE

In this review, we will address p53 functions as it relates to various neurodegenerative diseases, mainly its implications in the development of HIV-associated neurocognitive disorders.

CONCLUSION

p53 plays a pivotal role in the development of neurodegenerative diseases through its interaction with cellular factors, viral factors, and/or small RNAs that have the ability to promote the development of these diseases. Hence, inhibition of p53 may present an ideal target to restore neuronal functions.

The role of monocyte-lineage cells in human immunodeficiency virus persistence: mechanisms and progress

Human immunodeficiency virus type 1 (HIV-1) persistence is a major barrier to the successful treatment and eradication of acquired immunodeficiency syndrome (AIDS). In addition to resting CD4(+) T cells, a significant long-lived compartment of HIV-1 infection in vivo includes blood monocytes and tissue macrophages. Studying HIV-1 persistence in monocyte-lineage cells is critical because these cells are important HIV-1 target cells in vivo. Monocyte-lineage cells, including monocytes, dendritic cells (DCs) and macrophages, play a significant role in HIV-1 infection and transmission. These cells have been implicated as viral reservoirs that facilitate HIV-1 latency and persistence. A better understanding of HIV-1 interactions with monocyte-lineage cells can potentially aid in the development of new approaches for intervention. This minireview highlights the latest advances in understanding the role of monocyte-lineage cells in HIV-1 persistence and emphasizes new insights into the mechanisms underlying viral persistence.

Arc of a vicious circle: pathways activated by Mycobacterium tuberculosis that target the HIV-1 long terminal repeat

In this review, we examine how a subset of signal transduction cascades initiated by Mycobacterium tuberculosis (Mtb) infection modulates transcription mediated by the human immunodeficiency virus type 1 long terminal repeat (HIV-1 LTR). We describe two distinct phases of signaling that target transcription factors known to bind the HIV-1 LTR, and thus drive viral transcription and replication, in cells of the Mtb-infected host. First, Mtb-derived molecules, including cell wall components and DNA, interact with a number of host pattern recognition receptors. Second, cytokines and chemokines secreted in response to Mtb infection initiate signal transduction cascades through their cognate receptors. Given the variation in cell wall components among distinct clinical Mtb strains, the initial pattern recognition receptor interaction leading to direct LTR activation and differential cytokine and chemokine production is likely to be an important aspect of Mtb strain-specific regulation of HIV-1 transcription and replication. Improved understanding of these molecular mechanisms in the context of bacterial and host genetics should provide key insights into the accelerated viral replication and disease progression characteristic of HIV/TB coinfection.

Comparative antiviral activity of integrase inhibitors in human monocyte-derived macrophages and lymphocytes

The activity of raltegravir and 4 other integrase inhibitors (MK-2048, L870,810, IN2, and IN5) was investigated in primary human macrophages, PBMC and C8166-lymphocytic T cells, in order to determine their relative potency and efficacy in different cellular systems of HIV infection. Raltegravir showed better protective efficacy in all cell types; MK-2048, L870,810 and IN5 showed a potent anti-HIV-1 activity in macrophages, while in lymphocytes only MK-2048 and L870,810 showed an inhibitory effect comparable to raltegravir. IN2 was a poorly effective anti-HIV-1 compound in all cellular systems. All effective integrase inhibitors exhibited a potent antiviral activity against both X4 and R5 HIV-1 strains. In general, raltegravir, MK-2048, L870,810 and IN5 showed anti HIV activity similar or slightly higher in macrophages compared to PBMC and C8166 T cells: for MK-2048, the EC(50) was 0.4, 0.9, 11.5 nM in macrophages, in PBMCs and T cells, respectively; for L870,810, the EC(50) was 1.5, 14.3, and 10.6 nM, respectively; for IN5 the EC(50) was 0.5, 13.7, and 5.7 nM, respectively.

In vivo expression profile of the antiviral restriction factor and tumor-targeting antigen CD317/BST-2/HM1.24/tetherin in humans

Human CD317 is an intrinsic immunity factor that restricts the release of enveloped viruses, including the major pathogens HIV and Lassa virus, from infected cells in culture. Its importance for infection control in humans is unclear, due in part to its incompletely defined in vivo expression pattern. CD317 also has been proposed as a selective target for immunotherapy of multiple myeloma. To provide a framework for studies of the biological functions, regulation, and therapeutic potential of CD317, we performed microarray-based expression profiling in 468 tissue samples from 25 healthy organs from more than 210 patients. We found that CD317 protein was expressed to varying degrees in all organs tested and detected in a number of specialized cell types, including hepatocytes, pneumocytes, ducts of major salivary glands, pancreas and kidney, Paneth cells, epithelia, Leydig cells, plasma cells, bone marrow stromal cells, monocytes, and vascular endothelium. Although many of these cell types are in vivo targets for pathogenic viruses, restriction by CD317 or virus-encoded antagonists has been documented in only some of them. Limited cell type-dependent coexpression of CD317 with the IFN biomarker MxA in vivo and lack of responsive stimulation in organ explants suggest that interferons may only partially regulate CD317. This in vivo expression profiling sheds light on the biology and species-specificity of CD317, identifies multiple thus far unknown interaction sites of viruses with this restriction factor, and refutes the concept of its restricted constitutive expression and primary IFN inducibility. CD317's widespread expression calls into question its suitability as a target for immunotherapy.

SAMHD1: a new insight into HIV-1 restriction in myeloid cells

Human myeloid-lineage cells are refractory to HIV-1 infection. The Vpx proteins from HIV-2 and sooty mangabey SIV render these cells permissive to HIV-1 infection through proteasomal degradation of a putative restriction factor. Two recent studies discovered the cellular protein SAMHD1 to be this restriction factor, demonstrating that Vpx induces proteasomal degradation of SAMHD1 and enhances HIV-1 infection in myeloid-lineage cells. SAMHD1 functions as a myeloid-cell-specific HIV-1 restriction factor by inhibiting viral DNA synthesis. Here we discuss the implications of these findings in delineating the mechanisms of HIV-1 restriction in myeloid-lineage cells and the potential role of Vpx in lentiviral pathogenesis.

Exposure to apoptotic activated CD4+ T cells induces maturation and APOBEC3G-mediated inhibition of HIV-1 infection in dendritic cells

Dendritic cells (DCs) are activated by signaling via pathogen-specific receptors or exposure to inflammatory mediators. Here we show that co-culturing DCs with apoptotic HIV-infected activated CD4(+) T cells (ApoInf) or apoptotic uninfected activated CD4(+) T cells (ApoAct) induced expression of co-stimulatory molecules and cytokine release. In addition, we measured a reduced HIV infection rate in DCs after co-culture with ApoAct. A prerequisite for reduced HIV infection in DCs was activation of CD4(+) T cells before apoptosis induction. DCs exposed to ApoAct or ApoInf secreted MIP-1α, MIP-1β, MCP-1, and TNF-α; this effect was retained in the presence of exogenous HIV. The ApoAct-mediated induction of co-stimulatory CD86 molecules and reduction of HIV infection in DCs were partially abrogated after blocking TNF-α using monoclonal antibodies. APOBEC3G expression in DCs was increased in co-cultures of DCs and ApoAct but not by apoptotic resting CD4(+) T cells (ApoRest). Silencing of APOBEC3G in DC abrogated the HIV inhibitory effect mediated by ApoAct. Sequence analyses of an env region revealed significant induction of G-to-A hypermutations in the context of GG or GA dinucleotides in DNA isolated from DCs exposed to HIV and ApoAct. Thus, ApoAct-mediated DC maturation resulted in induction of APOBEC3G that was important for inhibition of HIV-infection in DCs. These findings underscore the complexity of differential DC responses evoked upon interaction with resting as compared with activated dying cells during HIV infection.

Architecture and regulation of the HIV-1 assembly and holding compartment in macrophages

Productive infection of macrophages is central to HIV-1 pathogenesis. Newly formed virions bud into a tubular membranous compartment that is contiguous with the plasma membrane. However, little is known about the structure of this compartment and its potential regulation by infection. Here we characterized this compartment in macrophages using electron tomography and electron microscopy with stereology. We found an intricate, interconnected membrane network that constitutes a preexisting physiologic structure in macrophages but which expands in size upon HIV-1 infection. Membranes required for this expansion were apparently derived from preexisting pools of plasma membrane. Physical connections between this compartment and the extracellular milieu were frequently made by tube-like structures of insufficient diameter for virion passage. We conclude that HIV-1 induces the expansion of a complex membranous labyrinth in macrophages in which the virus buds and can be retained, with potential consequences for transmission and immune evasion.

Proteomic analyses of monocytes obtained from Hispanic women with HIV-associated dementia show depressed antioxidants

PURPOSE

Monocyte ingress into the brain during progressive human immunodeficiency virus (HIV-1) infection parallels the severity of cognitive impairments. Although activated monocyte phenotypes emerge in disease, the functional correlates of these cells remain unresolved.

EXPERIMENTAL DESIGN

To this end, we studied the proteome of blood-derived monocytes obtained from Hispanic women with the most severe form of HIV-associated neurocognitive disorders, HIV-associated dementia (HAD). Monocytes isolated from peripheral blood mononuclear cells by CD14+ immunoaffinity column chromatography were >95% pure. Cells were recovered from four patients without evidence of cognitive impairment and five with HAD and analyzed by 2-D DIGE and tandem MS.

RESULTS

Importantly, ADP ribosylhydrolase, myeloperoxidase, thioredoxin, peroxiredoxin 3, NADPH, and GTPase-activating protein were all downregulated in HAD. In regards to myeloperoxidase, thioredoxin, and peroxiredoxin 3, these changes were validated in an additional cohort of 30 patients by flow cytometry.

CONCLUSIONS AND CLINICAL RELEVANCE

We conclude that deficits in monocyte antioxidants lead to neuronal damage through the loss of hydrogen peroxide scavenging capabilities; thus exposing neurons to apoptosis-inducing factors. Altered monocyte functions therefore may contribute to the development and progression of cognitive impairment.

Tetherin does not significantly restrict dendritic cell-mediated HIV-1 transmission and its expression is upregulated by newly synthesized HIV-1 Nef

Background

Dendritic cells (DCs) are among the first cells to encounter HIV-1 and play important roles in viral transmission and pathogenesis. Immature DCs allow productive HIV-1 replication and long-term viral dissemination. The pro-inflammatory factor lipopolysaccharide (LPS) induces DC maturation and enhances the efficiency of DC-mediated HIV-1 transmission. Type I interferon (IFN) partially inhibits HIV-1 replication and cell-cell transmission in CD4⁺ T cells and macrophages. Tetherin is a type I IFN-inducible restriction factor that blocks HIV-1 release and modulates CD4⁺ T cell-mediated cell-to-cell transmission of HIV-1. However, the role of type I IFN and tetherin in HIV-1 infection of DCs and DC-mediated viral transmission remains unknown.

Results

We demonstrated that IFN-alpha (IFNα)-induced mature DCs restricted HIV-1 replication and trans-infection of CD4⁺ T cells. Tetherin expression in monocyte-derived immature DCs was undetectable or very low. High levels of tetherin were transiently expressed in LPS- and IFNα-induced mature DCs, while HIV-1 localized into distinct patches in these DCs. Knockdown of induced tetherin in LPS- or IFNα-matured DCs modestly enhanced HIV-1 transmission to CD4⁺ T cells, but had no significant effect on wild-type HIV-1 replication in mature DCs. Intriguingly, we found that HIV-1 replication in immature DCs induced significant tetherin expression in a Nef-dependent manner.

Conclusions

The restriction of HIV-1 replication and transmission in IFNα-induced mature DCs indicates a potent anti-HIV-1 response; however, high levels of tetherin induced in mature DCs cannot significantly restrict wild-type HIV-1 release and DC-mediated HIV-1 transmission. Nef-dependent tetherin induction in HIV-1-infected immature DCs suggests an innate immune response of DCs to HIV-1 infection.

The oral commensal, Streptococcus gordonii, synergizes with Tat protein to induce HIV-1 promoter activation in monocytes/macrophages

Trans-activator of transcription (Tat) is an HIV-1 protein essential for viral replication. Oral periodontopathogens (e.g. Fusobacterium nucleatum) enhance HIV-1LTR promoter activation in monocytes/macrophages in absence of Tat; however, some oral commensals fail to trigger this response. We sought to determine the effect of Tat on HIV-1LTR promoter activation induced by the representative oral commensal Streptococcus gordonii in monocytes/macrophages. S. gordonii enhanced HIV-1LTR reactivation in THP89GFP (Tat(+)), but not in BF24 (Tat(-)) cells. Interestingly, S. gordonii, but not Streptococcus sanguinis enhanced HIV-1LTR activation in the presence of recombinant Tat in BF24 cells. This response correlated with IL-8 but not TNFα or IL-6 production, and was abrogated by the NFκB inhibitor BAY 11-7082. Kinetics of NFκB-RelA activation did not explain the S. gordonii-induced HIV-1LTR activation in presence of Tat. These results suggest that S. gordonii-induced HIV-1 reactivation in monocytes/macrophages is Tat-dependent and appears to involve NFκB activation.

Insights into cellular factors that regulate HIV-1 replication in human cells

Retroviruses integrate into the host cell's chromosome. Accordingly, many aspects of the life cycle of retroviruses like HIV-1 are intimately linked to the functions of cellular proteins and RNAs. In this review, we discuss in brief recent genomewide screens for the identification of cellular proteins that assist HIV-1 replication in human cells. We also review findings for other cellular moieties that help or restrict the viral life cycle.