Macrophages and the human immunodeficiency virus

Role of RIPK1 in SMAC mimetics-induced apoptosis in primary human HIV-infected macrophages

Macrophages serve as viral reservoirs due to their resistance to apoptosis and HIV-cytopathic effects. We have previously shown that inhibitor of apoptosis proteins (IAPs) confer resistance to HIV-Vpr-induced apoptosis in normal macrophages. Herein, we show that second mitochondrial activator of caspases (SMAC) mimetics (SM) induce apoptosis of monocyte-derived macrophages (MDMs) infected in vitro with a R5-tropic laboratory strain expressing heat stable antigen, chronically infected U1 cells, and ex-vivo derived MDMs from HIV-infected individuals. To understand the mechanism governing SM-induced cell death, we show that SM-induced cell death of primary HIV-infected macrophages was independent of the acquisition of M1 phenotype following HIV infection of macrophages. Instead, SM-induced cell death was found to be mediated by IAPs as downregulation of IAPs by siRNAs induced cell death of HIV-infected macrophages. Moreover, HIV infection caused receptor interacting protein kinase-1 (RIPK1) degradation which in concert with IAP1/2 downregulation following SM treatment may result in apoptosis of macrophages. Altogether, our results show that SM selectively induce apoptosis in primary human macrophages infected in vitro with HIV possibly through RIPK1. Moreover, modulation of the IAP pathways may be a potential strategy for selective killing of HIV-infected macrophages in vivo.

Pathogenesis of HIV-Related Lung Disease: Immunity, Infection, and Inflammation

Despite anti-retroviral therapy (ART), human immunodeficiency virus-1 (HIV)-related pulmonary disease continues to be a major cause of morbidity and mortality for people living with HIV (PLWH). The spectrum of lung diseases has changed from acute opportunistic infections resulting in death to chronic lung diseases for those with access to ART. Chronic immune activation and suppression can result in impairment of innate immunity and progressive loss of T cell and B cell functionality with aberrant cytokine and chemokine responses systemically as well as in the lung. HIV can be detected in the lungs of PLWH and has profound effects on cellular immune functions. In addition, HIV-related lung injury and disease can occur secondary to a number of mechanisms including altered pulmonary and systemic inflammatory pathways, viral persistence in the lung, oxidative stress with additive effects of smoke exposure, microbial translocation, and alterations in the lung and gut microbiome. Although ART has had profound effects on systemic viral suppression in HIV, the impact of ART on lung immunology still needs to be fully elucidated. Understanding of the mechanisms by which HIV-related lung diseases continue to occur is critical to the development of new preventive and therapeutic strategies to improve lung health in PLWH.

Synthesis and characterization of a long-acting emtricitabine prodrug nanoformulation

Purpose

A palmitoylated prodrug of emtricitabine (FTC) was synthesized to extend the drug’s half-life, antiretroviral activities and biodistribution.

Methods

A modified FTC prodrug (MFTC) was synthesized by palmitoyl chloride esterification. MFTC’s chemical structure was evaluated by nuclear magnetic resonance. The created hydrophobic prodrug nanocrystals were encased into a poloxamer surfactant and the pharmacokinetics (PK), biodistribution and antiretroviral activities of the nanoformulation (NMFTC) were assessed. The conversion of MFTC to FTC triphosphates was evaluated.

Results

MFTC coated with poloxamer formed stable nanocrystals (NMFTC). NMFTC demonstrated an average particle size, polydispersity index and zeta potential of 350 nm, 0.24 and −20 mV, respectively. Drug encapsulation efficiency was 90%. NMFTC was readily taken up by human monocyte-derived macrophages yielding readily detected intracellular FTC triphosphates and an extended PK profile.

Conclusion

NMFTC shows improved antiretroviral activities over native FTC. This is coordinate with its extended apparent half-life. The work represents an incremental advance in the development of a long-acting FTC formulation.

Anti-HIV Activities of Novel Nucleoside Analogues: Acyclic and Tricyclic Base Nucleosides

Two series of new nucleoside derivatives, acyclic nucleosides and tricyclic base nucleosides, were screened for cellular toxicity and against HIV-1. Compounds were tested on MT4, MT2, U937 cell lines and PBMCs in multiwell tissue culture plates. Cells were infected in vitro with 2 TCID50/105 cells or 0.2 TCID50/105 cells of HIV-1-LAV-1. Two out of eight tricyclic derivatives showed little cytotoxicity; at 100μM, only two acyclic compounds exhibited cellular toxicity in U937 cells. In vitro, none of these 19 compounds demonstrated any efficient activity against the lentiviral HIV infection and replication. Furthermore, combinations of these acyclonucleosides with ddC or AZT did not inhibit HIV-1-LAV-1 replication additively or synergistically. Because acyclonucleosides did not induce any cytotoxic effect, other compounds of this family should be investigated.

Didanosine

The evaluation and development of didanosine as a therapy for HIV-infection has demonstrated that results of cell-culture studies are only approximate predictors of clinical effects. Whereas the antiviral activity of didanosine is achieved in cell culture at concentrations much higher than those of zidovudine, the two drugs appear to achieve similar effects on markers of HIV-infection at similar clinical doses. The effect of the differing intracellular-half-life of the respective nucleoside triphosphates on the clinical effects is unknown. Similarly, preclinical toxicology studies, while suggesting a low potential for didanosine-induced haematological toxicities, did not predict the findings of peripheral neuropathy and pancreatitis in clinical studies. Thus, the results of controlled clinical studies are required in order to more fully define the therapeutic and safety profile of didanosine.

Inhibition of HIV-1 and LP-BM5 Replication in Macrophages by Dideoxycytidine and Dideoxycytidine 5′-Triphosphate

The antiviral agent 2′,3′-dideoxycytidine (ddC) has been shown to be active against HIV-1 infectivity. However, conflicting results have been reported concerning its efficacy in macrophages. Because macrophages possess low levels of the kinase(s) responsible for ddC phosphorylation, we investigated the ability of ddC and 2′,3′-dideoxycytidine 5′-trisphosphate (ddCTP) to suppress HIV-1 and LP-BM5 replication in these cells. Retrovirus replication was only partially inhibited in the two systems investigated by a high (1 μM) ddC concentration. The direct administration of ddCTP, using autologous red blood cells as a delivery system, was found to inhibit HIV-1 and LP-BM5 replication by more than 90% in macrophages without affecting major cell functions. These data, together with those already reported for FIV [Magnani et al. (1994) AIDS Res Hum Retroviruses 10: 1179-1186], suggest that the anabolic phosphorylation of ddC is an important determinant of its anti-HIV activity and that pharmacological interventions that modulate ddC metabolism may be useful for improving its antiretroviral activity in macrophages.

B, Golla K, Kondapi AK. Improved Safety, Bioavailability and Pharmacokinetics of Zidovudine through Lactoferrin Nanoparticles during Oral Administration in Rats

Zidovudine (AZT) is one of the most referred antiretroviral drug. In spite of its higher bioavailability (50–75%) the most important reason of its cessation are bone marrow suppression, anemia, neutropenia and various organs related toxicities. This study aims at the improvement of oral delivery of AZT through its encapsulation in lactoferrin nanoparticles (AZT-lactonano). The nanoparticles (NPs) are of 50–60 nm in size and exhibit 67% encapsulation of the AZT. They are stable in simulated gastric and intestinal fluids. Anti-HIV-1 activity of AZT remains unaltered in nanoformulation in acute infection. The bioavailability and tissue distribution of AZT is higher in blood followed by liver and kidney. AZT-lactonano causes the improvement of pharmacokinetic profile as compared to soluble AZT; a more than 4 fold increase in AUC and AUMC in male and female rats. The serum C_max for AZT-lactonano was increased by 30%. Similarly there was nearly 2-fold increase in T_max and t_1/2. Our in vitro study confirms that, the endosomal pH is ideal for drug release from NPs and shows constant release from up to 96h. Bone marrow micronucleus assay show that nanoformulation exhibits approximately 2fold lower toxicity than soluble form. Histopathological and biochemical analysis further confirms that less or no significant organ toxicities when nanoparticles were used. AZT-lactonano has shown its higher efficacy, low organs related toxicities, improved pharmacokinetics parameter while keeping the antiviral activity intact. Thus, the nanoformulation are safe for the target specific drug delivery.

Defining differential genetic signatures in CXCR4- and the CCR5-utilizing HIV-1 co-linear sequences

The adaptation of human immunodeficiency virus type-1 (HIV-1) to an array of physiologic niches is advantaged by the plasticity of the viral genome, encoded proteins, and promoter. CXCR4-utilizing (X4) viruses preferentially, but not universally, infect CD4⁺ T cells, generating high levels of virus within activated HIV-1-infected T cells that can be detected in regional lymph nodes and peripheral blood. By comparison, the CCR5-utilizing (R5) viruses have a greater preference for cells of the monocyte-macrophage lineage; however, while R5 viruses also display a propensity to enter and replicate in T cells, they infect a smaller percentage of CD4⁺ T cells in comparison to X4 viruses. Additionally, R5 viruses have been associated with viral transmission and CNS disease and are also more prevalent during HIV-1 disease. Specific adaptive changes associated with X4 and R5 viruses were identified in co-linear viral sequences beyond the Env-V3. The in silico position-specific scoring matrix (PSSM) algorithm was used to define distinct groups of X4 and R5 sequences based solely on sequences in Env-V3. Bioinformatic tools were used to identify genetic signatures involving specific protein domains or long terminal repeat (LTR) transcription factor sites within co-linear viral protein R (Vpr), trans-activator of transcription (Tat), or LTR sequences that were preferentially associated with X4 or R5 Env-V3 sequences. A number of differential amino acid and nucleotide changes were identified across the co-linear Vpr, Tat, and LTR sequences, suggesting the presence of specific genetic signatures that preferentially associate with X4 or R5 viruses. Investigation of the genetic relatedness between X4 and R5 viruses utilizing phylogenetic analyses of complete sequences could not be used to definitively and uniquely identify groups of R5 or X4 sequences; in contrast, differences in the genetic diversities between X4 and R5 were readily identified within these co-linear sequences in HIV-1-infected patients.

Small alveolar macrophages are infected preferentially by HIV and exhibit impaired phagocytic function

HIV-1-infected persons are at higher risk of lower respiratory tract infections than HIV-1-uninfected individuals. This suggests strongly that HIV-infected persons have specific impairment of pulmonary immune responses, but current understanding of how HIV alters pulmonary immunity is incomplete. Alveolar macrophages (AMs), comprising small and large macrophages, are major effectors of innate immunity in the lung. We postulated that HIV-1 impairs pulmonary innate immunity through impairment of AM physiological functions. AMs were obtained by bronchoalveolar lavage from healthy, asymptomatic, antiretroviral therapy-naive HIV-1-infected and HIV-1-uninfected adults. We used novel assays to detect in vivo HIV-infected AMs and to assess AM functions based on the HIV infection status of individual cells. We show that HIV has differential effects on key AM physiological functions, whereby small AMs are infected preferentially by the virus, resulting in selective impairment of phagocytic function. In contrast, HIV has a more generalized effect on AM proteolysis, which does not require direct viral infection. These findings provide new insights into how HIV alters pulmonary innate immunity and the phenotype of AMs that harbors the virus. They underscore the need to clear this HIV reservoir to improve pulmonary immunity and reduce the high incidence of lower respiratory tract infections in HIV-1-infected individuals.

HIV/SIV infection primes monocytes and dendritic cells for apoptosis

Subversion or exacerbation of antigen-presenting cells (APC) death modulates host/pathogen equilibrium. We demonstrated during in vitro differentiation of monocyte-derived macrophages and monocyte-derived dendritic cells (DCs) that HIV sensitizes the cells to undergo apoptosis in response to TRAIL and FasL, respectively. In addition, we found that HIV-1 increased the levels of pro-apoptotic Bax and Bak molecules and decreased the levels of anti-apoptotic Mcl-1 and FLIP proteins. To assess the relevance of these observations in the context of an experimental model of HIV infection, we investigated the death of APC during pathogenic SIV-infection in rhesus macaques (RMs). We demonstrated increased apoptosis, during the acute phase, of both peripheral blood DCs and monocytes (CD14⁺) from SIV⁺RMs, associated with a dysregulation in the balance of pro- and anti-apoptotic molecules. Caspase-inhibitor and death receptors antagonists prevented apoptosis of APCs from SIV⁺RMs. Furthermore, increased levels of FasL in the sera of pathogenic SIV⁺RMs were detected, compared to non-pathogenic SIV infection of African green monkey. We suggest that inappropriate apoptosis of antigen-presenting cells may contribute to dysregulation of cellular immunity early in the process of HIV/SIV infection.

Antigen-presenting cells (APCs) are critical for both innate and adaptive immunity. They have a profound impact on the hosts' ability to combat microbes. Dysfunction and premature death by apoptosis of APCs may contribute to an abnormal immune response unable to clear pathogens. Circulating blood monocytes exhibit developmental plasticity, with the capability of differentiating into either macrophages or dendritic cells (DCs), and they represent important cellular targets for HIV-1. We report that HIV infection renders monocytes/macrophages and DCs in vitro more prone to undergo apoptosis and this heightened susceptibility is associated with changes in the expression of anti- and pro-apoptotic molecules. Our results show that during the acute phase of SIV-infection of rhesus macaques, monocytes and DCs are more prone to die by apoptosis. They express lower levels of Mcl-1 and FLIP proteins, two anti-apoptotic molecules, but higher expression of the active form of Bax and Bak, the gatekeepers of the mitochondria, major sensor of the apoptotic machinery. Because the early events are important in the pathogenesis of this disease, early death of APCs should play a major role leading to the defective immune response. Strategies aimed at preventing death of APCs could be beneficial in helping the immune response to fight HIV-1.

Stavudine-loaded mannosylated liposomes: in-vitro anti-HIV-I activity, tissue distribution and pharmacokinetics

Cells of the mononuclear phagocyte system (MPS) are important hosts for human immunodeficiency virus (HIV). Lectin receptors, which act as molecular targets for sugar molecules, are found on the surface of these cells of the MPS. Stavudine-loaded mannosylated liposomal formulations were developed for targeting to HIV-infected cells. The mannose-binding protein concanavalin A was employed as model system for the determination of in-vitro ligand-binding capacity. Antiretroviral activity was determined using MT-2 cell line. Haematological changes, tissue distribution and pharmacokinetic studies of free, liposomal and mannosylated liposomal drug were performed following a bolus intravenous injection in Sprague-Dawley rats. The entrapment efficiency of mannosylated liposomes was found to be 47.H ± 1.57%. Protein-carbohydrate interaction has been utilized for the effective delivery of mannosylated formulations. Cellular drug uptake was maximal when mannosylated liposomes were used. MT2 cells treated continuously with uncoated liposomal formulation had p24 levels 8–12 times lower than the level of free drug solution. Further, the mannosylated liposomes have shown p24 levels that were 14–20 and 1.42.3 times lower than the level of free drug and uncoated liposomal formulation treatment, respectively. Similar results were observed when infected MT2 cells were treated overnight. Stavudine, either given plain or incorporated in liposomes, led to development of anaemia and leucocytopenia while mannosylated liposomes overcame these drawbacks. These systems maintained a significant level of stavudine in the liver, spleen and lungs up to 12 h and had greater systemic clearance as compared with free drug or the uncoated liposomal formulation. Mannosylated liposomes have shown potential for the site-specific and ligand-directed delivery systems with desired therapeutics and better pharmacological activity.

HIV-1 buds predominantly at the plasma membrane of primary human macrophages

HIV-1 assembly and release are believed to occur at the plasma membrane in most host cells with the exception of primary macrophages, for which exclusive budding at late endosomes has been reported. Here, we applied a novel ultrastructural approach to assess HIV-1 budding in primary macrophages in an immunomarker-independent manner. Infected macrophages were fed with BSA-gold and stained with the membrane-impermeant dye ruthenium red to identify endosomes and the plasma membrane, respectively. Virus-filled vacuolar structures with a seemingly intracellular localization displayed intense staining with ruthenium red, but lacked endocytosed BSA-gold, defining them as plasma membrane. Moreover, HIV budding profiles were virtually excluded from gold-filled endosomes while frequently being detected on ruthenium red-positive membranes. The composition of cellular marker proteins incorporated into HIV-1 supported a plasma membrane-derived origin of the viral envelope. Thus, contrary to current opinion, the plasma membrane is the primary site of HIV-1 budding also in infected macrophages.

NFAT5 regulates HIV-1 in primary monocytes via a highly conserved long terminal repeat site

To replicate, HIV-1 capitalizes on endogenous cellular activation pathways resulting in recruitment of key host transcription factors to its viral enhancer. RNA interference has been a powerful tool for blocking key checkpoints in HIV-1 entry into cells. Here we apply RNA interference to HIV-1 transcription in primary macrophages, a major reservoir of the virus, and specifically target the transcription factor NFAT5 (nuclear factor of activated T cells 5), which is the most evolutionarily divergent NFAT protein. By molecularly cloning and sequencing isolates from multiple viral subtypes, and performing DNase I footprinting, electrophoretic mobility shift, and promoter mutagenesis transfection assays, we demonstrate that NFAT5 functionally interacts with a specific enhancer binding site conserved in HIV-1, HIV-2, and multiple simian immunodeficiency viruses. Using small interfering RNA to ablate expression of endogenous NFAT5 protein, we show that the replication of three major HIV-1 viral subtypes (B, C, and E) is dependent upon NFAT5 in human primary differentiated macrophages. Our results define a novel host factor-viral enhancer interaction that reveals a new regulatory role for NFAT5 and defines a functional DNA motif conserved across HIV-1 subtypes and representative simian immunodeficiency viruses. Inhibition of the NFAT5-LTR interaction may thus present a novel therapeutic target to suppress HIV-1 replication and progression of AIDS.

Monocyte-derived macrophages and myeloid cell lines as targets of HIV-1 replication and persistence

HIV infection of mononuclear phagocytes (MP), mostly as tissue macrophages, is a dominant feature in the pathogenesis of HIV disease and its progression to AIDS. Although the general mechanism of infection is not dissimilar to that of CD4+ T lymphocytes occurring via interaction of the viral envelope with CD4 and a chemokine receptor (usually CCR5), other features are peculiar to MP infection. Among others, the long-term persistence of productive infection, sustained by the absence of substantial cell death, and the capacity of the virions to bud and accumulate in intracellular multivesicular bodies (MVB), has conferred to MP the role of "Trojan horses" perpetuating the chronic state of infection. Because the investigation of tissue macrophages is often very difficult for both ethical and practical reasons of accessibility, most studies of in vitro infection rely upon monocyte-derived macrophages (MDM), a methodology hampered by inter-patient variability and lack of uniformity of experimental protocols. A number of cell lines, mostly Mono Mac, THP-1, U937, HL-60, and their derivative chronically infected counterparts (such as U1 and OM-10.1 cell lines) have complemented the MDM system of infection providing useful information on the features of HIV replication in MP. This article describes and compares the most salient features of these different cellular models of MP infection by HIV.

Intracellular substrates for the primer-unblocking reaction by human immunodeficiency virus type 1 reverse transcriptase: detection and quantitation in extracts from quiescent- and activated-lymphocyte subpopulations

Treatment of human immunodeficiency virus type 1 (HIV-1)-infected patients with 3'-azido-3'-deoxythymidine (AZT) selects for mutant forms of viral reverse transcriptase (RT) with increased ability to remove chain-terminating nucleotides from blocked DNA chains. We tested various cell extracts for the presence of endogenous acceptor substrates for this reaction. Cell extracts incubated with HIV-1 RT and [(32)P]ddAMP-terminated DNA primer/template gave rise to (32)P-labeled adenosine 2',3'-dideoxyadenosine 5',5'''-P(1),P(4)-tetraphosphate (Ap(4)ddA), ddATP, Gp(4)ddA, and Ap(3)ddA, corresponding to the transfer of [(32)P]ddAMP to ATP, PP(i), GTP, and ADP, respectively. Incubation with [(32)P]AZT monophosphate (AZTMP)-terminated primer/template gave rise to the analogous (32)P-labeled AZT derivatives. Based on the rates of formation of the specific excision products, ATP and PP(i) levels were determined: ATP was present at 1.3 to 2.2 mM in H9 cells, macrophages, and unstimulated CD4(+) or CD8(+) T cells, while PP(i) was present at 7 to 15 microM. Under these conditions, the ATP-dependent reaction predominated, and excision by the AZT-resistant mutant RT was more efficient than wild type RT. Activated CD4(+) or CD8(+) T cells contained 1.4 to 2.7 mM ATP and 55 to 79 microM PP(i). These cellular PP(i) concentrations are lower than previously reported; nonetheless, the PP(i)-dependent reaction predominated in extracts from activated T cells, and excision by mutant and wild-type RT occurred with similar efficiency. While PP(i)-dependent excision may contribute to AZT resistance in vivo, it is likely that selection of AZT-resistant mutants occurs primarily in an environment where the ATP-dependent reaction predominates.

Endosomal membrane traffic: convergence point targeted by Mycobacterium tuberculosis and HIV

Inhibition of phagolysosome biogenesis in infected macrophages is a classical pathogenesis determinant of Mycobacterium tuberculosis. In this review we primarily cover the cellular mechanisms of M. tuberculosis phagosome maturation arrest. A detailed picture is beginning to emerge, involving regulators of membrane trafficking in mammalian cells and phagosomal interactions with endosomal organelles and the trans-Golgi network. We also present a hypothesis that overlaps may exist between the mycobacterial interference with the host cell membrane trafficking processes and the targeting of the late endosomal sorting machinery by HIV during viral budding in macrophages. We propose that interference with the endosomal sorting machinery contributes to the synergism between the two significant human diseases--AIDS and tuberculosis.

HIV-1 Tat protein upregulates inflammatory mediators and induces monocyte invasion into the brain

Impaired inflammatory functions may be critical factors in the mechanisms by which HIV-1 enters the CNS. Evidence indicates that a viral gene product, the protein Tat, can markedly contribute to these effects. In the present study we tested the hypothesis that Tat can upregulate the expression of inflammatory cytokines and adhesion molecules and facilitate the entry of monocytes into the brain. Expression of inflammatory mediators such as monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) was assessed in C57BL/6 mice injected with Tat(1-72) into the right hippocampus. In the Tat(1-72)-injected groups, mRNA and protein levels of MCP-1, TNF-alpha, VCAM-1, and ICAM-1 were markedly elevated compared to those in control animals. The most pronounced changes were observed in and around the injected hippocampus. Double-labeling immunohistochemistry demonstrated that inflammatory proteins were primarily expressed in activated microglial cells and perivascular cells. In addition, astrocytes and endothelial cells were susceptible to Tat(1-72)-induced inflammatory responses. These changes were associated with a substantial infiltration of monocytes into the brain. These data demonstrate that intracerebral administration of Tat can induce profound proinflammatory effects in the brain, leading to monocyte infiltration.

HIV-associated coronary artery disease

Cases, case series, and related articles on coronary artery disease in patients with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) identified through a comprehensive literature search were examined for clinical characteristics and angiographic findings of HIV-associated coronary artery disease. Among 129 identified cases, 91% were males. The mean age was 42.3 +/- 10.2 (SD) years (range, 23 to 77 years). The interval between the diagnosis of HIV infection and the diagnosis of coronary artery disease was 72 +/- 60 (SD) months. Degree of immunosuppression was variable (CD4 mean, 313 +/- 209 cells/mm3; range, 6-1070 cells/mm3). There was no correlation between the CD4 cell count and the development and progression of coronary artery disease. Similarly, the development and progression of coronary artery disease was independent of the presence of HIV-related opportunistic infections. Acute myocardial infarction was the initial presentation in 77% of patients. In 76 patients, information on diseased vessels was available: 36 (47%) patients had 3-vessel disease, 14 (18%) patients had 2-vessel disease, and 26 patients (35%) had 1-vessel disease. The left anterior descending artery was involved in 47 (62%) patients while the left circumflex and right coronary arteries were involved in 34 (45%) and 38 (50%) patients, respectively. Thirty-two (25%) patients underwent catheter-based or surgical revascularization. Data were not adequate to assess the prognosis following the acute coronary events or revascularization. The histologic characteristics unique to HIV-associated coronary arteriopathy were diffuse circumferential involvement of the vessel with an unusual proliferation of smooth muscle cells, mixed with abundant elastic fibers, resulting in endoluminal protrusions. Coronary artery disease was a late complication of AIDS.

Potential role for CD63 in CCR5-mediated human immunodeficiency virus type 1 infection of macrophages

Macrophages and CD4(+) lymphocytes are the principal target cells for human immunodeficiency virus type 1 (HIV-1) infection, but the molecular details of infection may differ between these cell types. During studies to identify cellular molecules that could be involved in macrophage infection, we observed inhibition of HIV-1 infection of macrophages by monoclonal antibody (MAb) to the tetraspan transmembrane glycoprotein CD63. Pretreatment of primary macrophages with anti-CD63 MAb, but not MAbs to other macrophage cell surface tetraspanins (CD9, CD81, and CD82), was shown to inhibit infection by several R5 and dualtropic strains, but not by X4 isolates. The block to productive infection was postfusion, as assessed by macrophage cell-cell fusion assays, but was prior to reverse transcription, as determined by quantitative PCR assay for new viral DNA formation. The inhibitory effects of anti-CD63 in primary macrophages could not be explained by changes in the levels of CD4, CCR5, or beta-chemokines. Infections of peripheral blood lymphocytes and certain cell lines were unaffected by treatment with anti-CD63, suggesting that the role of CD63 in HIV-1 infection may be specific for macrophages.

Mechanisms of enveloped RNA virus budding

To spread infection, enveloped viruses must bud from infected host cells. Recent research indicates that HIV and other enveloped RNA viruses bud by appropriating the cellular machinery that is normally used to create vesicles that bud into late endosomal compartments called multivesicular bodies. This new model of virus budding has many potential implications for cell biology and viral pathogenesis.

Human macrophages accumulate HIV-1 particles in MHC II compartments

Macrophages are important targets for HIV-1 infection and harbor the virions in an as yet unidentified organelle. To determine the location of HIV-1 in these cells, an extensive analysis of primary human macrophages infected in vitro with HIV-1 was carried out by immuno-electron microscopy. Virus particles were found to accumulate in intracellular multivesicular compartments which were enriched in major histocompatibility complex class II molecules and CD63. These features are characteristics of major histocompatibility complex class II compartments where maturing class II molecules acquire their peptide cargo. The membrane-delimited, electron-dense virus particles of 100-110 nm diameter labeled strongly for HIV-1 p24 antigen, major histocompatibility complex class II molecules, CD63 and, to a lesser extent for HIV-1 gp120 envelope protein and Lamp 1. Our data suggest that virus particles may access the lumen of the major histocompatibility complex class II compartment by budding from the limiting membrane, thus acquiring proteins of this membrane such as class II and CD63. Viral assembly and budding would therefore occur in macrophages by a process similar to the formation of the internal vesicles in multivesicular bodies and at the same location. This could account for the particular content in lipids and proteins previously found in the membrane wrapping HIV particles. Our observations also suggest direct fusion of the virus containing major histocompatibility complex class II compartment with the plasma membrane, leading to massive release of viral particles into the extracellular medium.

NF-kappaB cis-acting motifs of the human immunodeficiency virus (HIV) long terminal repeat regulate HIV transcription in human macrophages

The role of NF-kappaB in the reactivation of human immunodeficiency virus (HIV) from latency in CD4 T lymphocytes is well documented. However, its role in driving HIV transcription in human macrophages, which contain a constitutive nuclear pool of NF-kappaB, is less well understood. In this study we have investigated the role that the constitutive pool of NF-kappaB and the NF-kappaB cis-acting motifs of the HIV long terminal repeat (LTR) play in regulating HIV transcription in human monocytic cells and primary macrophages. Inhibition of the constitutive nuclear pool of NF-kappaB (RelA and RelB) in the promonocytic U937 cell line using dominant-negative IkappaBalpha significantly decreases HIV replication. Moreover, it is demonstrated that in the differentiated monocytic cell line THP1, which contains a constitutive nuclear pool of NF-kappaB (RelB),an HIV provirus containing mutations of the kappaB cis-acting sites in the LTR is transcriptionally impaired. Reduction of the constitutive pool of NF-kappaB in human macrophages by an adenovirus vector expressing a dominant-negative IkappaBalpha also reduces HIV transcription. Lastly, mutation of the NF-kappaB cis-acting sites in the LTR of an R5 HIV provirus completely abrogates the first cycle of HIV transcription. These studies indicate that the cis-acting NF-kappaB motifs of the HIV LTR are critical in initiating HIV transcription in human macrophages and suggest that the constitutive nuclear pool of NF-kappaB is important in regulating HIV transcription in these cells.

Human immunodeficiency virus type 1 entry into macrophages mediated by macropinocytosis

Whereas human immunodeficiency virus (HIV) infects various cell types by fusion at the plasma membrane, we observed a different entry route in human primary macrophages, in which macropinocytosis is active. Shortly after exposure of macrophages to HIV-1 and irrespective of viral envelope-receptor interactions, particles were visible in intracellular vesicles, which were identified as macropinosomes. Most virions appeared subsequently degraded. However, fusion leading to capsid release in the cytosol and productive infection could take place inside vesicles when particles were properly enveloped. These observations provide new insights into HIV-1 interactions with a cell target relevant to pathogenesis. They may have implications for the design of soluble inhibitors aimed at interfering with the fusion or entry processes.

Regulation of class II expression in monocytic cells after HIV-1 infection

Human macrophage hybridoma cells were used to study HLA-DR expression after HIV-1 infection. HLA-DR surface expression was lost 2 wk after infection that was associated with decreased mRNA transcription. Transfecting HLA-DR-alpha and HLA-DR-beta cDNA driven by a nonphysiological CMV promoter restored expression, suggesting that regulatory DNA-binding proteins may be affected by HIV-1 infection. There was no protein binding to conserved class II DNA elements (W/Z/S box, X-1 and X-2 boxes, and Y box) in a HIV-1-infected human macrophage hybridoma cell line, 43(HIV), and in primary monocytes that lost HLA-DR expression after HIV-1(BaL) infection. PCR analysis of the HIV-1-infected cells that lost HLA-DR expression revealed mRNA for W/Z/S (RFX-5), X-1 (RFX-5), X-2 (hX-2BP), and one Y box DNA-binding protein (NF-YB), and CIITA, a non-DNA-binding protein necessary for class II transcription. There was no mRNA for the Y box-binding protein, NF-YA. However, HLA-DR expression could be restored by transfection with NF-YA driven by a CMV promoter, although HLA-DR failed to localize in either the late endosomes, lysosomes, or acidic compartments. This was associated with a loss of class II-associated invariant chain peptide and leupeptin-induced protein in the 43(HIV) cells. To address this further, non-HIV-1-infected 43 cells were infected with vaccinia virus containing HIV-1 gag, nef, pol, and env proteins. HLA-DR failed to localize in neither the late endosomes, lysosomes, or acidic compartments in the vaccinia-infected cells containing HIV-1 env protein. HIV-1 appears to have multiple effects on class II expression in monocytic cells that may contribute to the immune defects seen in HIV-1-infected patients.

The effects of HIV infection on endothelial function

Endothelial dysfunction and/or injury is pivotal to the development of cardiovascular and inflammatory pathology. Endothelial dysfunction and/or injury has been described in Human Immunodeficiency Virus (HIV) infection. Elaboration of circulating markers of endothelial activation, such as soluble adhesion molecules and procoagulant proteins, occurs in HIV infection. Certain endothelial cells, such as those lining liver sinusoids, human umbilical vein endothelial cells, bone marrow stromal endothelial cells or brain microvascular endothelial cells, have been shown to be variably permissive for HIV infection. Entry of virus into endothelial cells may occur via CD4 antigen or galactosyl-ceramide receptors. Other mechanisms of entry including chemokine receptors have been proposed. Nevertheless, endothelial activation may also occur in HIV infection either by cytokines secreted in response to mononuclear or adventitial cell activation by virus or else by the effects of the secreted HIV-associated proteins, gp 120 (envelope glycoprotein) and Tat (transactivator of viral replication) on endothelium. Enhanced adhesiveness of endothelial cells, endothelial cell proliferation and apoptosis as well as activation of cytokine secretion have all been demonstrated. Synergy between select inflammatory cytokines and viral proteins in inducing endothelial injury has been shown. In HIV infection, dysfunctional or injured endothelial cells potentiate tissue injury, inflammation and remodeling, and accelerate the development of cardiovascular disease.

HIV-1 infects and alters immune function of a monocyte subset expressing low CD14 surface phenotype

Monocytes represent a leukocyte subset that express high levels of CD14 on their surface (CD14-high). These cells play a critical role in the pathogenesis of HIV-1 infection. In the present study, we have identified a monocyte subset expressing an extremely low level of CD14 (CD14-low), and examined their susceptibility to HIV-1 infection. Phenotypic analysis by flow cytometry of these cells revealed a low level of CD4, but the absence of CD3, CD14, CD19, and CD83 surface markers. Both CD14-low and CD14-high cell populations expressed CD13 and CD33 markers on their surface, suggesting these cells to be of myeloid origin. Morphologically, CD14-low cells were indistinguishable from CD14-high cells. CD14-low cells were susceptible to infection with a monocytotropic strain of HIV-1 (HIVADA). However, like CD14-high monocytes, CD14-low cells could not be productively infected with a T cell tropic strain of HIV-1 (H9/HTLV(IIIB)). Similar to CD14-high monocytes, CD14-low cells were capable of inducing antigen-stimulated CD4+ T-cell proliferation. HIV-1 infection substantially reduced their ability to induce antigen-stimulated T-cell proliferation. These data indicate that CD14-low cells belong to the monocyte lineage and may play an important role in the immunopathogenesis of HIV-1 infection.

Ikappakappa mediates NF-kappaB activation in human immunodeficiency virus-infected cells

Human monocytes and macrophages are persistent reservoirs of human immunodeficiency virus (HIV) type-1. Persistent HIV infection of these cells results in increased levels of NF-kappaB in the nucleus secondary to increased IkappaBalpha, IkappaBbeta, and IkappaBepsilon degradation, a mechanism postulated to regulate viral persistence. To characterize the molecular mechanisms regulating HIV-mediated degradation of IkappaB, we have sought to identify the regulatory domains of IkappaBalpha targeted by HIV infection. Using monocytic cells stably expressing different transdominant molecules of IkappaBalpha, we determined that persistent HIV infection of these cells targets the NH2 but not the COOH terminus of IkappaBalpha. Further analysis demonstrated that phosphorylation at S32 and S36 is necessary for HIV-dependent IkappaBalpha degradation and NF-kappaB activation. Of the putative N-terminal IkappaBalpha kinases, we demonstrated that the Ikappakappa complex, but not p90(rsk), is activated by HIV infection and mediates HIV-dependent NF-kappaB activation. Analysis of viral replication in cells that constitutively express IkappaBalpha negative transdominant molecules demonstrated a lack of correlation between virus-induced NF-kappaB (p65/p50) nuclear translocation and degree of viral persistence in human monocytes.

Dynamics of co-infection with M. Tuberculosis and HIV-1

Since 1985, there has been a renewed epidemic of tuberculosis (TB) that was previously thought to be in check. There is evidence to believe the main factor for this resurgence has been the human immunodeficiency virus (HIV). Co-infection with HIV and M. Tuberculosis has profound implications for the course of both diseases. This study represents a first attempt to understand how the introduction of an opportunistic infection, namely Mycobacterium tuberculosis, the bacteria that causes TB, affects the dynamic interaction of HIV-1 and the immune system. We create a mathematical model using ordinary differential equations to describe the interaction of HIV and TB with the immune system. It is known that infection with TB can decrease the CD4(+) T cell counts-a key marker of AIDS progression; thus, it shortens survival in HIV infected individuals. Another main marker for HIV progression is the viral load. If this load is increased due to the presence of opportunistic infections, the disease progression is much more rapid. We also explore the effects of drug treatment on the TB infection in the doubly-infected patient.

Inhibition of HIV type 1 replication in chronically infected monocytes and lymphocytes by retrovirus-mediated gene transfer of anti-Rev single-chain variable fragments

We investigated a strategy for gene therapy, intracellular expression of anti-HIV-1 Rev single-chain variable fragments (SFvs), in promonocytic (U1) and T (ACH-2) cell lines latently infected with HIV-1. The cellular and molecular mechanisms leading to activation of latent integrated HIV-1 provirus in U1 and ACH-2 cells have been well delineated. These cells produce HIV-1 in response to stimulation with certain cytokines. U1 and ACH-2 cells were transduced with a murine retroviral shuttle vector that expresses anti-Rev SFv (pLXSN-D8SFv-Rev) or with a control murine leukemia virus (MLV) vector (pLXSN). Tumor necrosis factor alpha (TFNalpha)-, interleukin 6 (IL-6)-, and phorbol myristate acid (PMA)-induced HIV-1 expression, as determined by reverse transcriptase (RT) assay, was significantly inhibited in cells transduced with pLXSN-D8SFv-Rev, compared with cells transduced with pLXSN. In addition, pLXSN-D8SFv-Rev-transduced cells, when incubated with monokine-enriched supernatants of human peripheral blood monocyte cultures, produced significantly less HIV-1 than did cells transduced with pLXSN. This resistance to cytokine-induced HIV-1 expression was demonstrated in SFv-transduced U1 and ACH-2 cells maintained in G418-free medium for 2 months. These data suggest that feasibility of utilizing various anti-HIV-1 SFvs to block activation of HIV-1 infection in vivo.

Chronically HIV-1-Infected Monocytic Cells Induce Apoptosis in Cocultured T Cells

We have previously developed a human macrophage hybridoma model system to study the effect of HIV-1 infection on monocytic function. Upon coculture of one chronically (35 days postinfection) HIV-1-infected human macrophage hybridoma cell line, 43HIV, there was a dose-dependent decrease in the viability of cocultured Ag-stimulated T cells associated with an increase in DNA strand breaks. Enhanced apoptosis was determined by labeling with biotinylated dUTP and propidium iodide, increased staining with annexin V, increased side light scatter and expression of CD95, and decreased forward light scatter and expression of Bcl-2. There was also increased DNA strand breaks as determined by propidium iodide staining in unstimulated T cells cocultured with 43HIV and in T cells stimulated with anti-CD3 mAb and PHA. Pretreatment with 5145, a human polyclonal anti-gp120 Ab that recognizes the CD4 binding region, as well as with an anti-Fas ligand mAb blocked apoptosis in CD4+ T cells but not in CD8+ T cells. A soluble factor with a Mr below 10,000 Da was defined that induced apoptosis in CD4+ and CD8+ T cells and B cells. SDS-PAGE analysis of the active fractions revealed a band of 6000 Da that, after electroelution, had proapoptotic activity. The pI of the activity was estimated to be between 6.5 and 7.0. In conclusion, chronically HIV-1-infected monocytic cells induce apoptosis in bystander-, Ag-, anti-CD3-, and mitogen-stimulated T cells by multiple factors, which may contribute to the depletion of lymphocytes induced by HIV-1.

Enhancement of HIV-1 replication in human macrophages is induced by CD8+ T cell soluble factors

We previously reported that CD8+ T cell-derived factors enhanced HIV long terminal repeat (LTR)-mediated gene expression and replication in monocytic cell lines. We now report that replication of NSI and SI primary isolates of HIV-1 in human macrophages were significantly enhanced by CD8+ T cell supernatants. The CD8-mediated enhancement of HIV replication was abrogated by pertussis toxin in a dose-dependent manner. The sensitivity to pertussis toxin suggests that the CD8+ T cell-derived enhancing factor is acting through a G protein-coupled signalling pathway. Enhanced HIV replication in macrophages was accompanied by increased levels of HIV-1 mRNA, suggesting that CD8 enhancement was mediated at the transcriptional level. Interestingly, the replication of HIV(Bal), which replicates to high levels in macrophages, was not significantly modulated by culture with CD8+ T cell supernatants. Although direct co-culture of activated CD8+ T cells with HIV(Ada)-infected macrophages did not modulate replication, separation of the CD8+ T cells from macrophages in transwell cultures resulted in significant enhancement of replication. The inability to detect a modulatory effect in direct co-cultures appeared to be due to non-specific lysis of infected macrophages. Thus, soluble factors produced by CD8+ T cells exert strong enhancing effects on HIV-1 replication in human macrophages.

Epstein-Barr Virus Infects and Induces Apoptosis in Human Neutrophils

The role of neutrophils during Epstein-Barr virus (EBV) infection is not known. Disruption of the initial and nonspecific immune response may favor the spread of EBV infection. We have previously shown that EBV interacts with human neutrophils and modulates protein expression. In this study we have investigated the ability of EBV to infect neutrophils. Electron microscopy studies showed penetration of virus and its subsequent localization to the nucleus. The presence of viral genomes in isolated nuclei from neutrophils was also shown by polymerase chain reaction (PCR). Expression of viral transcripts like EBNA-2 (Epstein-Barr nuclear antigen-2) and ZEBRA (BamHI Z EBV replication activator) was not detected by reverse transcriptase (RT)-PCR, suggesting that EBV does not seem to establish a latent or a lytic infection in neutrophils. However, at 20 hours post-EBV infection, 77% of cells were apoptotic as compared to 22% in uninfected cell cultures, as evaluated by flow cytometry. This EBV-induced apoptosis was prevented by the addition of granulocyte-macrophage colony-stimulating factor to the cell cultures. Apoptotic cell death seems to implicate the Fas/Fas ligand (L) pathway, as reflected by an increase of Fas/Fas L expression on neutrophils treated with EBV and an increase of soluble Fas L, which may function in an autocrine/paracrine pathway to mediate cell death. Lastly, EBV genome was detected from neutrophils of infectious mononucleosis (IM) patients in contrast to neutrophils obtained from healthy EBV-seropositive donors. Our findings on the interactions of EBV with neutrophils will then provide new insights on the immunosuppressive effects associated with EBV infection.

Cytosolic Gag p24 as an index of productive entry of human immunodeficiency virus type 1

We have investigated the cellular uptake of Gag p24 shortly after exposure of cells to human immunodeficiency virus (HIV) particles. In the absence of envelope glycoprotein on virions or of viral receptors or coreceptors at the cell surface, p24 was incorporated in intracellular vesicles but not detected in the cytosolic subcellular fraction. When appropriate envelope-receptor interactions could occur, the nonspecific vesicular uptake was still intense and cytosolic p24 represented 10 to 40% of total intracellular p24. The measurement of cytosolic p24 early after exposure to HIV type 1 is a reliable assay for investigating virus entry and early events leading to authentic cell infection.

Human Immunodeficiency Virus-1 env Impairs Fcγ Receptor-Mediated Phagocytosis Via a Cyclic Adenosine Monophosphate-Dependent Mechanism

Human immunodeficiency virus (HIV)-1 expression in mononuclear phagocytes is associated with multiple functional defects, including phagocytosis. To assess Fcγ receptor (FcγR) function in cells expressing HIV-1, human promonocytic cells (U937) acutely or chronically infected with HIV-1, or stably transfected with a noninfectious reverse transcriptase (RT) defective HIV-1 provirus (Δpol), were treated with phorbol 12-myristate 13-acetate for 48 hours and tested for their ability to ingest sheep erythrocytes coated with IgG (E-IgG). HIV-1–infected or transfected U937 cells ingested 50% to 65% fewer E-IgG than controls despite normal surface expression of FcγRs. HIV-1 specifically impaired FcγR-mediated phagocytosis, as ingestion of complement-coated erythrocytes was unaffected. U937 cells transfected with an env deficient mutant of HIV-1 ingested E-IgG normally, suggesting that the expression of HIV-1 env was required for HIV-1 to inhibit FcγR-mediated phagocytosis. Expression of HIV-1 in U937 cells was associated with an increased accumulation of intracellular cyclic adenosine monophosphate (cAMP); addition of the adenylate cyclase inhibitor 2′,5′-dideoxyadenosine to these cells decreased intracellular cAMP levels to that of controls and restored FcγR-mediated phagocytosis. Addition of either interferon (IFN)-γ or an inhibitor of cAMP-dependent protein kinase A (KT 5720) to HIV-1–transfected U937 cells also restored FcγR-mediated phagocytosis. Expression of HIV-1 induces a specific defect of FcγR function in mononuclear phagocytes that correlates with increased levels of cAMP, and can be corrected by pharmacologic manipulation.

Differential effects on HIV-1 gene regulation by EBV in T lymphocytic and promonocytic cells transduced to express recombinant human CR2

A panel of human hematopoietic cell lines was genetically engineered to express recombinant complement receptor 2 (CR2 or CD21), which is also the Epstein-Barr virus (EBV) receptor. The panel was composed of SupT1, J1.1, and U1.HIV cells. The latter is a promonocytic cell line, whereas the other two are T lymphocytic cell lines. J1.1 and U1.HIV cells are latently infected by human immunodeficiency virus type 1 (HIV-1). These three cell lines were transduced with a murine leukemia virus (MLV)-based retroviral vector system. CR2 was efficiently and consistently expressed on the cell membranes, conferring enhanced susceptibility to EBV infection. The efficient expression of recombinant CR2 in cell lines of hematopoietic origin allowed for study of the interaction between EBV infection and HIV-1 gene regulation in suitable cell-culture models. The effects of EBV and HIV-1 coinfection results were cell-type dependent. In the two T lymphocytic cell lines, HIV-1 expression was rapidly and persistently down-regulated by EBV. Conversely, in the promonocytic cell line U1.HIV-CR2, HIV-1 expression was transiently enhanced by EBV. The EBV and HIV-1 coinfection result in U1.HIV-CR2 cells is potentially important, as the activation of HIV-1 gene expression in monocyte-like cells may play a crucial role in the mechanism of CD4+ T cell depletion by apoptosis. Therefore, the U1.HIV-CR2 cell line may represent a useful cell-culture system to study the synergism between EBV and HIV-1 in inducing apoptosis in primary CD4+ T cells.

2',3'-Dideoxycytidine cytotoxicity in human macrophages

Human macrophages when cultured for several weeks in the presence of therapeutically relevant 2',3'-dideoxycytidine (ddC) concentrations show a time-dependent decay in mitochondrial DNA content. This decay is associated with a reduction of Rhodamine 123 fluorescence, a marker for mitochondrial membrane potential suggesting that impairment of mitochondrial functions occurs. Mitochondrial metabolic impairment was confirmed by direct evaluation of lactate production, which is markedly increased in cells treated with ddC. The activity of protein kinase C and intracellular free Ca2+ upon addition of phorbol 12-myristate 13-acetate (PMA) were lower in the drug-treated cells compared to controls. A 50% reduction in O2-release was also found upon PMA stimulation. Fluorescent latex beads, yeast and bacteria phagocytosis were normal, but intracellular bacteria killing was markedly impaired in ddC-exposed macrophages. Thus, ddC exerts a delayed mitochondrial toxicity also on differentiated macrophages with impairment of several metabolic properties and O2 production causing a reduced ability of these phagocytic cells to kill phagocytosed bacteria.

Activation of endothelial cells via antibody-enhanced dengue virus infection of peripheral blood monocytes

Although endothelial cells have been speculated to be a target in the pathogenesis of dengue hemorrhagic fever (DHF), there has been little evidence linking dengue virus infection to any alteration in endothelial cell function. In this study, we show that human umbilical vein endothelial cells become activated when exposed to culture fluids from dengue virus-infected peripheral blood monocytes. Maximum activation was achieved with culture fluids from monocytes in which virus infection was enhanced by the addition of dengue virus-immune serum, thus correlating with epidemiological evidence that prior immunity to dengue virus is a major risk factor for DHF. Activation was strongest for endothelial cell expression of VCAM-1 and ICAM-1. In contrast, activation of endothelial cell E-selectin expression appeared to be more transient, as indicated by its detection at 3 h, but not at 16 h, of treatment. Treatment of monocyte culture fluids with anti-tumor necrosis factor alpha (TNF-alpha) antibody largely abolished the activation effect (as measured by endothelial cell expression of ICAM-1), whereas treatment with IL-1beta receptor antagonist had a much smaller inhibitory effect on activation. Endothelial cells inoculated directly with dengue virus or with virus-antibody combinations were poorly infectable (compared to Vero cells or peripheral blood monocytes), and virus-inoculated endothelial cells showed no increased expression of VCAM-1, ICAM-1, or E-selectin. Taken together, the results strongly indicate that dengue virus can modulate endothelial cell function by an indirect route, in which a key intermediary is TNF-alpha released from virus-infected monocytes.

Analysis of CD8+ T lymphocyte-mediated nonlytic suppression of autologous and heterologous primary human immunodeficiency virus type 1 isolates

Nonlytic CD8+ T lymphocyte antiviral factor (CAF) activity has been described as having an important role in the clinical course of human immunodeficiency virus type 1 (HIV-1) infection. Testing of CAF activity against autologous viruses isolated at approximately the same time points showed that CD8+ T lymphocytes from long-term survivors indeed possessed high CAF activity. However, in four of six progressors to AIDS, we observed the same amount of CAF activity in the face of increasing cellular HIV-1 load. In the other two progressors, CAF activity seemed preserved over time whereas the susceptibility of the virus isolate obtained late in infection seemed to be diminished. In a heterologous system, CAF activity of CD8+ T lymphocytes from 13 HIV-1-positive individuals did not correlate with CD4+ T lymphocyte counts. In two of three patients, syncytium-inducing (SI) HIV-1 variants, which are associated with a progressive clinical course, appeared to have a somewhat reduced susceptibility to CAF activity as compared to their coexisting non-SI HIV-1 variants. In a large donor group, suppression of SI isolates (as compared to non-SI isolates) mediated by heterologous CD8+ T lymphocytes was reduced. CD8+ T lymphocytes from five of six HIV-1-positive individuals suppressed HIV-1 replication in macrophages. CD8+ T lymphocytes from noninfected donors, even from cord blood, already had high CAF activity, suggesting that induction of this activity is neither virus nor HIV-1 specific.

Priming of human CD4+ antigen-specific T cells to undergo apoptosis by HIV-infected monocytes. A two-step mechanism involving the gp120 molecule

The study of the pathology of HIV-1 infection in chimpanzees supports the idea of the crucial role of HIV-infected monocytes in the pathogenesis of AIDS, although viral mechanisms that lead to T cell dysfunction and deletion during HIV infection are still unclear. We show here that HIV-1-infected antigen-presenting monocytes (APCs) are able to prime in vitro non-HIV-infected antigen-specific CD4+ T cell lines or peripheral blood CD4+ T cells to undergo apoptosis after antigen-specific restimulation. The priming of T cells for apoptosis occurs in the absence of HIV replication in the T cells. Priming for apoptosis required two concomitant signals present on the same APC, an antigenic stimulus and a second signal provided by the HIV gp120 protein as demonstrated by the use as APCs of EBV-LCLs infected with different recombinant deleted proviruses or transfected with different HIV proteins. These results provide a mechanism for the priming for apoptosis of T cells in HIV-infected patients, implicating a role for HIV-infected APCs in the induction of T cell dysfunction and depletion in AIDS.

Activation of human immunodeficiency virus long terminal repeat by arachidonic acid

Arachidonic acid is the precursor of highly reactive mediators, including prostaglandins and leukotrienes, and the most abundant n-6 polyunsaturated fatty acid in mammalian cell membranes. It is released from phospholipids upon many inflammatory stimuli. In this study, a chloramphenicol acyltransferase reporter gene, under control of the human immunodeficiency virus-1 long terminal repeat, was strongly induced upon treating human promonocytes with arachidonic acid. The n-3 fatty acid eicosapentenoic, found in abundance in fish oil, had no effect. HIV-1 long terminal repeat activation by arachidonic acid was suppressed by inhibitors of both lipoxygenase and cyclooxygenase pathways, suggesting that metabolites, rather than arachidonic acid itself, mediated the stimulatory effect. This is the first report linking HIV-1 expression to the metabolism of arachidonic acid.

A cytopathic infectivity assay of human immunodeficiency virus type 1 in human primary macrophages

In addition to CD4+ T lymphocytes, cells of monocyte/macrophage lineage are a major target for human immunodeficiency virus type 1 (HIV-1) infection. In vitro studies of HIV-1 infection in human monocyte-derived macrophages can be undertaken by a reproducible cell-based assay. A macrophage-based infectivity assay was developed based on the semi-quantitative scoring of HIV-1 induced cytopathology in monolayer macrophage cultures. The assay exhibited dilution-dependent linearity with all three primary macrophage-tropic isolates tested. The end-point infectivity titers determined by this assay correlated with the results obtained by detecting viral p24 antigen in the culture supernatant. The applications of the assay in both neutralization and anti-viral protocols yielded identical results with the more time-consuming and costly p24 formats. Since the assay offers a simple and low-cost method of measuring HIV-1 infectivity in human primary macrophages, it can be used quite easily for large-scale screening or evaluation of candidate vaccines and anti-viral agents.

Effects of dietary n-3 fatty acid supplementation in men with weight loss associated with the acquired immune deficiency syndrome: Relation to indices of cytokine production

Cytokines may be involved in weight loss and disturbances of metabolism associated with human immunodeficiency virus (HIV) infection. Dietary n-3 fatty acids reduce the production of interleukin-1 (IL-1) and tumor necrosis factor (TNF) by peripheral blood mononuclear cells (PBMC) in normal humans and prevent IL-1 and TNF anorexia in animals. Accordingly, we studied the nutritional and metabolic effects of a 10-week trial of dietary fish oil (MaxEPA 18 g/day) in men with weight loss due to acquired immune deficiency syndrome (AIDS). Twenty men were enrolled, and 16 completed the 10-week supplementation period. Prior weight loss was 13.7 +/- 1.8 kg(17.4 +/- 1.6% body weight, means +/- SE). Food intake, body composition, blood chemistries, serum cytokine concentrations, in vitro production of IL-1 and TNF by PBMC, and clinical course were followed. A subset of subjects (n=12) underwent stable isotope infusions to measure de novo hepatic lipogenesis (DNL), an in vivo metabolic index that is influenced by cytokine presence and has previously been found to be elevated in AIDS. An unsupplemented group of men with AIDS wasting (10.4 +/- 2.4 kg weight loss, 13.1 +/- 2.2% body weight) was monitored for 10 weeks as controls. Baseline food intake (2,395 +/- 177 kcal/day and 95.1 +/- 7.2 g protein/day), body weight, percent fat, and fat-free mass were unchanged over the 10-week supplementation period. Serum triglycerides were reduced in hypertriglyceridemic subjects, confirming compliance with fish oil supplementation and suggesting that their hypertriglyceridemia was at least in part due to overproduction. Serum TNF and IL-1 were undetectable before or after fish oil supplementation. Serum interferon alpha (IFN) was measurable but did not change. In vitro production of IL-1 and TNF by PBMC was markedly reduced both at baseline and after fish oil supplementation in this population, even in the presence of new AIDS complications, compared with normal controls. The metabolic measurement DNL fell and weight was gained (2.1 +/- 1.3 kg) in subjects who did not develop new AIDS-related complications, but further increases in DNL and further weight loss were observed in subjects who developed a new AIDS complication (p<0.05 for interaction between new complication and change in DNL). No changes in body weight, food intake, serum triglycerides, serum cytokines, or DNL were observed in the unsupplemented group. We conclude that fish oil is a weak anticytokine agent that is unable to overcome the metabolic and nutritional consequences of acute AIDS-related complications but may exert a clinical anticytokine effect in stable AIDS patients. Cytokine production by PBMC is not a useful or reliable marker of in vivo cytokine activity in AIDS patients with weight loss. In contrast, an integrative functional index that is sensitive to cytokine presence in tissues (hepatic DNL) correlated with clinical response. These findings are relevant to the design of future studies of more potent anticytokine agents, such as thalidomide.

Murine AIDS, a key to understanding retrovirus-induced immunodeficiency

A murine AIDS model, induced by LP-BM5 murine leukemia virus (MuLV), has helped to investigate pathogenesis of acquired immunodeficiency syndrome (AIDS), cofactor involvement, and new treatment tests. LP-BM5 MuLV-infected mice characteristically develop hypergammaglobulinemia, splenomegaly, lymphadenopathy, T-cell functional deficiency, B-cell dysfunction, and, in the later stages, neurological signs including paralysis as well as susceptibility to opportunistic infections. The similarities between murine AIDS and human AIDS are striking, with similar changes in immune functions, T-cell differentiation, cytokine production, disease resistance, and oxidative stress. The well-characterized murine immunological system, availability of inbred strains, economy of using mice versus primate model, and similarities in immunodeficiency caused by human immunodeficiency virus (HIV) encouraged rapid development of the LP-BM5 murine AIDS model in the past decade.

Activation of caprine arthritis-encephalitis virus long terminal repeat by gamma interferon

Caprine arthritis-encephalitis virus (CAEV) is a lymphotropic lentivirus whose replication increases during monocyte maturation. We examined gene expression directed by the CAEV long terminal repeat (LTR) in a promonocytic cell line stimulated with several agents. Our results demonstrate that the CAEV LTR is activated by treatment of immature monocytes with gamma interferon (IFN-gamma) or a phorbol ester but not with tumor necrosis factor alpha or lipopolysaccharide. The cis-acting element in the LTR for the IFN-gamma response localizes to a duplicated 70-bp motif that contains an IFN-gamma response element, the gamma-activated site. One copy of the motif is necessary and sufficient for the response to IFN-gamma. Multiple copies contribute to basal transcriptional activity in the context of a heterologous promoter. This IFN-gamma response element in the CAEV LTR differs from the element required for the response to phorbol esters. Thus, activation of the CAEV LTR in monocytes that are stimulated by IFN-gamma, a cytokine that is secreted in response to viral infections, could contribute to conversion from latent to high-level viral replication in infected hosts.

Analysis of recombinant and native CD4 by one- and two-dimensional gel electrophoresis

Knowledge of CD4 conformation within the membranes of human lymphoid and monocytoid cells is essential for a clear understanding of its function as a ligand for major histocompatibility complex II (MHC) molecules in T cell activation and for gp120 in human immunodeficiency virus (HIV) infection. The charge and structure of native (nCD4) and soluble recombinant CD4 (rCD4) were examined by one- and two-dimensional (2-DE) electrophoresis antigen mapping and silver staining. Recombinant CD4 was partitioned by nonequilibrium pH gradient electrophoresis (NEPHGE) and revealed a number of differentially charged 44 kDa species (pI > 9.5). Biotinylation (4 h, room temperature) of rCD4 yielded a single labelled species on sodium dodedyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with an increased apparent molecular mass to 50 kDa, consistent with a maximal incorporation of approximately 18 molecules of biotin per rCD4 molecule. The milder biotinylation (15 min, 4 degrees C) of cell-(CEM-T4, THP-1) expressed CD4 was not accompanied by any apparent alteration in molecular weight, nor abrogation of CD4 antigenicity. This was determined by isolation of nCD4 by immunoprecipitation and SDS-PAGE immunoblotting, using anti-CD4 mAbs (leu3a, OKT4A, Q4120, T4, OKT4, Q425) and by flow cytometry (leu4a, T4). The immunoprecipitation of full-length native CD4 from lymphoid MT2 and CEM-T4 cell extracts, however, revealed both monomeric and higher-order CD4 antigen complexes by immunoblotting. These studies describe the biotinylation, 1-DE and 2-DE of CD4 preparations, and indicate the capacity of CD4 of lymphocytes to form complexes which may influence CD4 conformation and epitope availability.

Human plasma enhances the infectivity of primary human immunodeficiency virus type 1 isolates in peripheral blood mononuclear cells and monocyte-derived macrophages

Physiological microenvironments such as blood, seminal plasma, mucosal secretions, or lymphatic fluids may influence the biology of the virus-host cell and immune interactions for human immunodeficiency virus type 1 (HIV-1). Relative to media, physiological levels of human plasma were found to enhance the infectivity of HIV-1 primary isolates in both phytohemagglutinin-stimulated peripheral blood mononuclear cells and monocyte-derived macrophages. Enhancement was observed only when plasma was present during the virus-cell incubation and resulted in a 3- to 30-fold increase in virus titers in all of the four primary isolates tested. Both infectivity and virion binding experiments demonstrated a slow, time-dependent process generally requiring between 1 and 10 h. Human plasma collected in anticoagulants CPDA-1 and heparin, but not EDTA, exhibited this effect at concentrations from 90 to 40%. Furthermore, heat-inactivated plasma resulted in a loss of enhancement in peripheral blood mononuclear cells but not in monocyte-derived macrophages. Physiological concentrations of human plasma appear to recruit additional infectivity, thus increasing the infectious potential of the virus inoculum.