Replication In Human Macrophages Research Articles

Multiple ecto-nucleoside triphosphate diphosphohydrolases facilitate intracellular replication of Legionella pneumophila.

Legionella pneumophila is an opportunistic pathogen that replicates within alveolar macrophages resulting in the onset of severe atypical pneumonia. Previously we have identified Lpg1905, a eukaryotic-type ecto-NTPDase (nucleoside triphosphate diphosphohydrolase) from L. pneumophila that was required for optimal intracellular replication and virulence in a mouse lung infection model. In the present study, we characterized the activity of a second eukaryotic-type NTPDase, Lpg0971, from L. pneumophila. We observed that recombinant Lpg0971 hydrolysed only ATP and exhibited divalent cation preference for manganese (II) ions. Similar to lpg1905, an lpg0971 mutant carrying the plasmid pMIP was attenuated in a mouse lung infection model and impaired for replication in human macrophages and amoebae. Increased trafficking of the LCV (Legionella-containing vacuole) to a LAMP-1 (lysosome-associated membrane protein-1)-positive compartment was observed for both the lpg1905 and lpg0971 mutants carrying pMIP. Complementation with either lpg1905 or lpg0971 restored intracellular replication, suggesting that a minimum level of ATPase activity was required for this function. A double lpg1905/0971 mutant was not more impaired for intracellular replication than the single mutants and complementation of the double mutant with lpg0971, but not lpg1905, restored intracellular replication. This suggested that although the NTPDases have overlapping activities they have distinct functions. Unlike many eukaryotic-type proteins from L. pneumophila, neither Lpg1905 nor Lpg0971 were translocated into the host cell by the Dot/Icm (defective in organelle trafficking/intracellular multiplication) typeIV secretion system. Overall our data suggest that the ability of L. pneumophila to replicate in eukaryotic cells relies in part on the ability of the pathogen to hydrolyse ATP within an intracellular compartment.

Sub-inhibitory concentrations of trans-cinnamaldehyde attenuate virulence in Cronobacter sakazakii in vitro.

Cronobacter sakazakii is a foodborne pathogen, which causes a life-threatening form of meningitis, necrotizing colitis and meningoencephalitis in neonates and children. Epidemiological studies implicate dried infant formula as the principal source of C. sakazakii. In this study, we investigated the efficacy of sub-inhibitory concentrations (SIC) of trans-cinnamaldehyde (TC), an ingredient in cinnamon, for reducing C. sakazakii virulence in vitro using cell culture, microscopy and gene expression assays. TC significantly (p ≤ 0.05) suppressed C. sakazakii adhesion to and invasion of human and rat intestinal epithelial cells, and human brain microvascular endothelial cells. In addition, TC inhibited C. sakazakii survival and replication in human macrophages. We also observed that TC reduced the ability of C. sakazakii to cause cell death in rat intestinal cells, by inhibiting nitric oxide production. Results from gene expression studies revealed that TC significantly downregulated the virulence genes critical for motility, host tissue adhesion and invasion, macrophage survival, and LPS (Lipopolysaccharide) synthesis in C. sakazakii. The efficacy of TC in attenuating these major virulence factors in C. sakazakii underscores its potential use in the prevention and/or control of infection caused by this pathogen.

Targeting of the Small GTPase Rab6A′ by the Legionella pneumophila Effector LidA

When the bacterium Legionella pneumophila, the causative agent of Legionnaires' disease, is phagocytosed by alveolar macrophages, it delivers a large number of effector proteins through its Dot/Icm type IV secretion system into the host cell cytosol. Among those proteins is LidA, an effector that interacts with several host GTPases of the Rab family, including Rab6A', a regulator of retrograde vesicle trafficking within eukaryotic cells. The effect of LidA on Rab6A' function and the role of Rab6A' for L. pneumophila growth within host cells has been unclear. Here, we show that LidA preferentially binds Rab6A' in the active GTP-bound conformation. Rab6 binding occurred through the central region of LidA and followed a stoichiometry for LidA and Rab6A' of 1:2. LidA maintained Rab6A' in the active conformation by efficiently blocking the hydrolysis of GTP by Rab6A', even in the presence of cellular GTPase-activating proteins, suggesting that the function of Rab6A' must be important for efficient intracellular replication of L. pneumophila. Accordingly, we found that production of constitutively inactive Rab6A'(T27N) but not constitutively active Rab6A'(Q72L) significantly reduced the ability of L. pneumophila to initiate intracellular replication in human macrophages. Thus, the presence of an active pool of Rab6 within host cells early during infection is required to support efficient intracellular growth of L. pneumophila.

The Tim3–Galectin 9 Pathway Induces Antibacterial Activity in Human Macrophages Infected with Mycobacterium tuberculosis

T cell Ig and mucin domain 3 (Tim3) is an inhibitory molecule involved in immune tolerance, autoimmune responses, and antiviral immune evasion. However, we recently demonstrated that Tim3 and Galectin-9 (Gal9) interaction induces a program of macrophage activation that results in killing of Mycobacterium tuberculosis in the mouse model of infection. In this study, we sought to determine whether the Tim3-Gal9 pathway plays a similar role in human pulmonary TB. We identified that pulmonary TB patients have reduced expression of Tim3 on CD14(+) monocytes in vivo. By blocking Tim3 and Gal9 interaction in vitro, we show that these molecules contribute to the control of intracellular bacterial replication in human macrophages. The antimicrobial effect was partially dependent on the production of IL-1β. Our results establish that Tim3-Gal9 interaction activates human M. tuberculosis -infected macrophages and leads to the control of bacterial growth through the production of the proinflammatory cytokine IL-1β. Data presented in this study suggest that one of the potential pathways activated by Tim3/Gal9 is the secretion of IL-1β, which plays a crucial role in antimicrobial immunity by modulating innate inflammatory networks.

Vitamin D: An Adjunct to Antiretroviral Therapy?

Vitamin D is best known for its effects on bone health, but a growing appreciation of its many immunomodulatory actions has prompted significant recent interest in its potential to prevent and treat diverse viral and bacterial infections [1–4]. Much of this research has focused on the question of whether vitamin D supplementation might slow progression of disease caused by human immunodeficiency virus (HIV) and prevent tuberculosis and other opportunistic infections in HIV-infected people [5]. Physiological concentrations of calcitriol, the active vitamin D metabolite, inhibit HIV replication in human macrophages in vitro and restrict growth of Mycobacterium tuberculosis through the induction of autophagy [6, 7]. Observational studies conducted in HIVinfected people who are not taking antiretroviral therapy (ART) have reported associations between vitamin D deficiency and susceptibility to tuberculosis, upper respiratory tract infection, and oral candidiasis [8, 9], raising the possibility that supplementation might reduce susceptibility to infections in this patient group. Surely, though, once a potent pharmacological therapy like ART is initiated, isn’t deficiency in a mere micronutrient unlikely to influence clinical outcomes in HIV-infected people? Not so, according to a cohort study published in this issue of the Journal [10]. Sudfeld and colleagues studied 1103 HIV-infected adults in Tanzania who were taking ART and participating in a randomized controlled trial of a multivitamin supplement that did not contain vitamin D. Clinical assessments were performed at monthly intervals, and the median duration of follow-up was 20.6 months. After multivariate adjustment, vitamin D deficiency (defined as a serum concentration of 25-hydroxyvitamin D of 10% weight loss (HR, 2.10; P = .02) but not with risk of malaria, pneumonia, or anemia. A milder degree of deficiency, termed “vitamin D insufficiency” and defined as a serum 25-hydroxyvitamin D concentration of 20–30 ng/mL, did not associate with any of these outcomes. Is the reported association between baseline vitamin D deficiency and increased risk of tuberculosis likely to be causal? In favor of this conclusion, the association survived statistical adjustment for a number of potential confounders of the relationship between vitamin D status and risk of opportunistic infection, including sex, age, season of sampling, body mass index, measures of HIV disease stage at baseline, and ART regimen. The authors also went to considerable lengths to investigate whether this association arose as a result of reverse causality, by excluding from their analysis individuals who developed tuberculosis within a month of enrollment. Notably, the association between baseline vitamin D deficiency and increased risk of subsequent tuberculosis was still observed even when diagnoses of pulmonary tuberculosis arising in the first 2 months of the study were excluded in a sensitivity analysis. This finding is significant, as tuberculosis itself might contribute to vitamin D deficiency, by reducing patients’ sun exposure or increasing consumption of 25-hydroxyvitamin D by activated macrophages. The observation that vitamin D deficiency preceded the onset of tuberculosis in the present study is consistent with findings from a cohort study conducted in HIVuninfected patients [11], and it effectively excludes reverse causality as an explanation for the association between vitamin D deficiency and tuberculosis risk reported here. A final point in favor of a causal interpretation is the biological plausibility of the hypothesis: in Received and accepted 31 October 2012; electronically published 16 November 2012. Correspondence: Adrian R. Martineau, MRCP, PhD, Centre for Primary Care and Public Health, Barts and The London School of Medicine, Queen Mary University of London, 58 Turner St, London E1 2AB, United Kingdom (a.martineau@ qmul.ac.uk). The Journal of Infectious Diseases 2013;207:373–5 © The Author 2012. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. permissions@oup.com. DOI: 10.1093/infdis/jis697

Identification of critical host mitochondrion-associated genes during Ehrlichia chaffeensis infections.

Ehrlichia chaffeensis is an obligate intracellular bacterium that causes human monocytic ehrlichiosis (HME). To determine what host components are important for bacterial replication, we performed microarray analysis on Drosophila melanogaster S2 cells by comparing host gene transcript levels between permissive and nonpermissive conditions for E. chaffeensis growth. Five-hundred twenty-seven genes had increased transcript levels unique to permissive growth conditions 24 h postinfection. We screened adult flies that were mutants for several of the "permissive" genes for the ability to support Ehrlichia replication. Three additional D. melanogaster fly lines with putative mutations in pyrimidine metabolism were also tested. Ten fly lines carrying mutations in the genes CG6479, separation anxiety, chitinase 11, CG6364 (Uck2), CG6543 (Echs1), withered (whd), CG15881 (Ccdc58), CG14806 (Apop1), CG11875 (Nup37), and dumpy (dp) had increased resistance to infection with Ehrlichia. Analysis of RNA by quantitative real-time reverse transcription-PCR (qRT-PCR) confirmed that the bacterial load was decreased in these mutant flies compared to wild-type infected control flies. Seven of these genes (san, Cht11, Uck2, Echs1, whd, Ccdc58, and Apop1) encoded proteins that had mitochondrial functions or could be associated with proteins with mitochondrial functions. Treatment of THP-1 cells with double-stranded RNA to silence the human UCK2 gene indicates that the disruption of the uridine-cytidine kinase affects E. chaffeensis replication in human macrophages. Experiments with cyclopentenyl cytosine (CPEC), a CTP synthetase inhibitor and cytosine, suggest that the nucleotide salvage pathway is essential for E. chaffeensis replication and that it may be important for the provision of CTP, uridine, and cytidine nucleotides.

Vitamin D Inhibits Human Immunodeficiency Virus Type 1 and Mycobacterium tuberculosis Infection in Macrophages through the Induction of Autophagy

Low vitamin D levels in human immunodeficiency virus type-1 (HIV) infected persons are associated with more rapid disease progression and increased risk for Mycobacterium tuberculosis infection. We have previously shown that 1α,25-dihydroxycholecalciferol (1,25D3), the active form of vitamin D, inhibits HIV replication in human macrophages through the induction of autophagy. In this study, we report that physiological concentrations of 1,25D3 induce the production of the human cathelicidin microbial peptide (CAMP) and autophagic flux in HIV and M. tuberculosis co-infected human macrophages which inhibits mycobacterial growth and the replication of HIV. Using RNA interference for Beclin-1 and the autophagy-related 5 homologue, combined with the chemical inhibitors of autophagic flux, bafilomycin A1, an inhibitor of autophagosome-lysosome fusion and subsequent acidification, and SID 26681509 an inhibitor of the lysosome hydrolase cathepsin L, we show that the 1,25D3-mediated inhibition of HIV replication and mycobacterial growth during single infection or dual infection is dependent not only upon the induction of autophagy, but also through phagosomal maturation. Moreover, through the use of RNA interference for CAMP, we demonstrate that cathelicidin is essential for the 1,25D3 induced autophagic flux and inhibition of HIV replication and mycobacterial growth. The present findings provide a biological explanation for the benefits and importance of vitamin D sufficiency in HIV and M. tuberculosis-infected persons, and provide new insights into novel approaches to prevent and treat HIV infection and related opportunistic infections.

An NLRP7-containing inflammasome mediates recognition of microbial lipopeptides and restrict intracellular bacterial replication in human macrophages (114.6)

Abstract Nod-like receptors (NLRs) emerged as central cytosolic pattern recognition receptors (PRRs). However, the function of the majority of NLRs is currently unknown. We identified that NLRP7 functions as a PRR in primary human macrophages. Activation of NLRP7 by cytosolic microbial acylated lipopeptides (acLP) causes ASC-dependent inflammasome formation in a cytosolic high-molecular weight complex, Caspase-1 activation and maturation and release of interleukin (IL)-1β and IL-18. Reconstitution of an NLRP7/ASC/pro-Caspase-1 inflammasome, but not of an NLRP3/ASC/pro-Caspase-1 inflammasome is sufficient to respond to intracellular delivery of acLP. However, in macrophages both NLRP7 and TLR2 are required for the acLP-mediated release of IL-1β. While TLR2 is necessary for the transcription of pro-IL-1β and pro-IL-18, NLRP7 mediates the Caspase-1-dependent maturation and release of both cytokines. Therefore, NLRP7 and TLR2 contribute to the host defense against intracellular Gram positive bacteria, since knock-down of either NLRP7 or TLR2 promotes intracellular replication of Listeria monocytogenes and knock-down of NLRP7 also increases the intracellular replication of Staphylococcus aures. Our study therefore increases our currently limited understanding of NLR activation, inflammasome assembly and maturation of IL-1β and IL-18 in human macrophages.

Proteolytic targeting of Rab29 by an effector protein distinguishes the intracellular compartments of human-adapted and broad-host Salmonella

Unlike broad-host Salmonella serovars, which cause self-limiting disease, Salmonella enterica serovar Typhi can infect only humans causing typhoid fever, a life-threatening systemic disease. The molecular bases for these differences are presently unknown. Here we show that the GTPase Rab29 (Rab7L1) distinguishes the intracellular vacuole of human-adapted and broad-host Salmonella serovars. A screen to identify host factors required for the export of typhoid toxin, which is exclusively encoded by the human-specific Salmonella enterica serovars Typhi (S. Typhi) and Paratyphi (S. Paratyphi) identified Rab29. We found that Rab29 is recruited to the S. Typhi-containing vacuole but not to vacuoles containing broad-host Salmonella. We observed that in cells infected with broad-host Salmonella Rab29 is specifically cleaved by the proteolytic activity of GtgE, a unique type III secretion effector protein that is absent from S. Typhi. An S. Typhi strain engineered to express GtgE and therefore able to cleave Rab29 exhibited increased intracellular replication in human macrophages. These findings indicate significant differences in the intracellular biology of human-adapted and broad-host Salmonella and show how subtle differences in the assortment of effector proteins encoded by highly related pathogens can have a major impact in their biology.

Antiviral effect of a selective COX-2 inhibitor on H5N1 infection in vitro

A selective cyclooxygenase-2 (COX-2) inhibitor has been previously shown to suppress the hyper-induced pro-inflammatory responses in H5N1 infected primary human cells. Here, we demonstrate that COX-2 inhibitors suppress H5N1 virus replication in human macrophages suggesting that H5N1 virus replication (more so than seasonal H1N1 virus) is dependent on activation of COX-2 dependent signaling pathways in host cells. COX-2 and its downstream signaling pathways deserve detailed investigation as a novel therapeutic target for treatment of H5N1 disease.

Importance of Phagosomal Functionality for Growth Restriction of Mycobacterium tuberculosis in Primary Human Macrophages

The best characterized survival mechanism of Mycobacterium tuberculosis inside the macrophage is the inhibition of phagosomal maturation. Phagosomal maturation involves several steps including fusion with lysosomes and acidification. However, it has not been elucidated which components of phagosomal maturation correlate with growth restriction of virulent mycobacteria in human macrophages, and we aimed to study this. We infected human monocyte-derived macrophages with M. tuberculosis and assessed bacterial replication, translocation of CD63 to the phagosome, and phagosomal acidification. We found that unstimulated human macrophages were able to control infection with M. tuberculosis upon inoculation at a low multiplicity of infection (MOI) of 1, but not at a high MOI of 10. The low MOI resulted in a macrophage-controlled balance between host cells and bacteria. Both H37Rv and H37Ra infection, at high and low MOI, led to equally ineffective translocation of CD63 to the phagosome. On the other hand, acidification of mycobacterial phagosomes was more efficient at MOI 1 than 10 with both mycobacterial strains, consistent with a direct or indirect role for phagosomal acidification in restricting M. tuberculosis growth. Furthermore, inhibition of the vacuolar H⁺-ATPase as well as of cathepsin D led to enhanced mycobacterial replication inside the macrophage. This again shows the importance of phagosomal acidification for control of mycobacterial growth, through the activation of lysosomal hydrolases. We conclude that acidification and related functional aspects of the mature phagosome are important factors for restriction of M. tuberculosis replication in human macrophages.

The CDK inhibitor p21Cip1/WAF1 is induced by FcγR activation and restricts HIV-1 replication in human macrophages

Background Macrophages are major targets of human immunodeficiency virus type 1 (HIV-1) infection. We have previously shown that the engagement of the activating Fc receptors of the IgG (FcγR) by immune complexes (IC) suppresses the replication of HIV-1 and related lentiviruses in monocyte-derived macrophages, inhibiting both the accumulation of reverse transcripts and the proviral integration [1].

Human Immunodeficiency Virus (HIV) Infection of Human Macrophages Is Increased by Dopamine: A Bridge between HIV-Associated Neurologic Disorders and Drug Abuse

The prevalence of human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) that result from HIV infection of the central nervous system is increasing. Macrophages, the primary target for HIV within the central nervous system, play a central role in HIV-induced neuropathogenesis. Drug abuse exacerbates HAND, but the mechanism(s) by which this increased neuropathology results in more severe forms of HAND in HIV-infected drug abusers is unclear. The addictive and reinforcing effects of many drugs of abuse, such as cocaine and methamphetamine, are mediated by increased extracellular dopamine in the brain. We propose a novel mechanism by which drugs of abuse intensify HIV neuropathogenesis through direct effects of the neurotransmitter dopamine on HIV infection of macrophages. We found that macrophages express dopamine receptors 1 and 2, and dopamine activates macrophages by increasing ERK 1 phosphorylation. Our results demonstrate for the first time that dopamine increases HIV replication in human macrophages and that the mechanism by which dopamine mediates this change is by increasing the total number of HIV-infected macrophages. This increase in HIV replication is mediated by activation of dopamine receptor 2. These findings suggest a common mechanism by which drugs of abuse enhance HIV replication in macrophages and indicate that the drug abuse-heightened levels of central nervous system dopamine could increase viral replication, thereby accelerating the development of HAND.

A new homodimer of aciclovir as a prodrug with increased solubility and antiviral activity

Aciclovir (ACV) is the drug of choice against herpes simplex virus type 1 (HSV-1) infection. However, its limited solubility in water and limited oral bioavailability represent the main limitations of this drug. Utilising a plaque reduction assay, this study assessed the antiherpetic activity of a new homodimer of ACV (ACVp 2ACV) with a higher water solubility. ACVp 2ACV markedly inhibited HSV-1 replication in Vero cells [50% effective concentration (EC 50) of 2.8 μM vs. 6.6 μM for ACV] and was non-toxic in the cells at concentrations ≤15 μM. ACVp 2ACV encapsulated in erythrocytes provides effective protection against HSV-1 replication in human macrophages and also partially against the HSV-1 thymidine kinase-deficient strain. Thus, ACVp 2ACV acts as an effective antiviral prodrug against HSV-1.

Epitope-Driven TB Vaccine Development: A Streamlined Approach Using Immuno-Informatics, ELISpot Assays, and HLA Transgenic Mice

New vaccine candidates that might better control the worldwide prevalence of Mycobacterium tuberculosis (Mtb) have yet to be described. Strong CD4+ T cell-mediated immune response (CMI) is correlated with protection from the development of TB disease; however, the selection of suitable vaccine antigens has been thwarted by the size and complexity of the (Mtb) proteome, and by the relative difficulty of delivering these antigens in the right immunological context. One possible solution is to develop immunotherapeutic vaccines for TB that are based on T cell epitopes representing multiple antigens. This text illustrates the stepwise development of epitope-driven vaccines from in silico epitope mapping to testing the vaccine in a live Mtb challenge model. First, we used the whole genome Mtb microarray to identify bacterial proteins expressed under the conditions thought to model Mtb survival and replication in human macrophages. Eighteen of these proteins were also found by Behr et al. to be absent from at least one strain of BCG; the sequences of these eighteen proteins were then screened for T-cell epitopes using the immuno-informatics algorithm, EpiMatrix. Of the seventeen representative epitopes evaluated in ELISpot assays, all seventeen were confirmed to elicit interferon (IFN)-gamma secretion by PBMC from Mtb-exposed subjects. A parallel live Mtb challenge study in mice showed prototype epitope-based TB vaccines to be robustly immunogenic but not as effective as BCG. These experiments illustrate the use of immuno-informatics tools for vaccine development and describe a pathway for the development of a more effective, epitope-driven, immunotherapeutic vaccine for TB.

The engagement of activating FcγRs inhibits primate lentivirus replication in human macrophages

The engagement of activating FcγRs inhibits primate lentivirus replication in human macrophages

Mycobacterium tuberculosis-induced CXCR4 and chemokine expression leads to preferential X4 HIV-1 replication in human macrophages

Mycobacterium tuberculosis-induced CXCR4 and chemokine expression leads to preferential X4 HIV-1 replication in human macrophages

Rhinovirus Replication in Human Macrophages Induces NF-κB-Dependent Tumor Necrosis Factor Alpha Production

Rhinoviruses (RV) are the major cause of acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD). Rhinoviruses have been shown to activate macrophages, but rhinovirus replication in macrophages has not been reported. Tumor necrosis factor alpha (TNF-alpha) is implicated in the pathogenesis of acute exacerbations, but its cellular source and mechanisms of induction by virus infection are unclear. We hypothesized that rhinovirus replication in human macrophages causes activation and nuclear translocation of NF-kappaB, leading to TNF-alpha production. Using macrophages derived from the human monocytic cell line THP-1 and from primary human monocytes, we demonstrated that rhinovirus replication was productive in THP-1 macrophages, leading to release of infectious virus into supernatants, but was limited in monocyte-derived macrophages, likely due to type I interferon production, which was robust in monocyte-derived but deficient in THP-1-derived macrophages. Similar to bronchial epithelial cells, only small numbers of cells supported complete virus replication. We demonstrated RV-induced activation of NF-kappaB and colocalization of p65/NF-kappaB nuclear translocation with virus replication in both macrophage types. The infection induced TNF-alpha release in a time- and dose-dependent, RV serotype- and receptor-independent manner and was largely (THP-1 derived) or completely (monocyte derived) dependent upon virus replication. Finally, we established the requirement for NF-kappaB but not p38 mitogen-activated protein kinase in induction of TNF-alpha. These data suggest RV infection of macrophages may be an important source of proinflammatory cytokines implicated in the pathogenesis of exacerbations of asthma and COPD. They also confirm inhibition of NF-kappaB as a promising target for development of new therapeutic intervention strategies.

Interleukin-10 inhibits HIV-1 LTR-directed gene expression in human macrophages through the induction of cyclin T1 proteolysis

Regulation of HIV-1 replication in human monocytes/macrophages occurs at multiple levels including transcription of the proviral genome, which depends on virally encoded Tat protein. Interleukin-10 (IL-10), an anti-inflammatory cytokine which is up-regulated during disease progression of AIDS, has been reported to suppress HIV-1 replication in macrophages at a post-entry stage of the virus life cycle. Our previous studies have demonstrated that Tat function is regulated during the differentiation of monocyte-derived macrophages (MDMs) in a manner that correlates with the early induction and subsequent shut-off of its cellular cofactor cyclin T1. Here, we report that IL-10 down-regulates cyclin T1 expression through the induction of proteasome-mediated proteolysis in human macrophages. Using a reporter virus that is deficient in Tat function, we also demonstrate that IL-10 inhibits HIV-1 gene expression in a Tat-dependent manner. Together, these results suggest that the down-regulation of cyclin T1, and consequently Tat function, contributes to the suppressive effect of IL-10 on HIV-1 replication in human macrophages.

HIV regulation of the IL-7R: a viral mechanism for enhancing HIV-1 replication in human macrophages in vitro

We report a novel mechanism, involving up-regulation of the interleukin (IL)-7 cytokine receptor, by which human immunodeficiency virus (HIV) enhances its own production in monocyte-derived macrophages (MDM) in vitro. HIV-1 infection or treatment of MDM cultures with exogenous HIV-1 Tat(86) protein up-regulates the IL-7 receptor (IL-7R) alpha-chain at the levels of steady-state RNA, protein, and functional IL-7R on the cell surface (as measured by ligand-induced receptor signaling). This IL-7R up-regulation is associated with increased amounts of HIV-1 virions in the supernatants of infected MDM cultures treated with exogenous IL-7 cytokine. The overall effect of IL-7 stimulation on HIV replication in MDM culture supernatants is typically in the range of one log and greater. The results are consistent with a model in which HIV infection produces the Tat protein, which in turn up-regulates IL-7R in a paracrine manner. This results in increased IL-7R signaling in response to the IL-7 cytokine, which ultimately promotes early events in HIV replication, including binding/entry and possibly other steps prior to reverse transcription. The results suggest that the effects of IL-7 on HIV replication in MDM should be considered when analyzing and designing clinical trials involving treatment of patients with IL-7 or Tat vaccines.