Negative regulation of human immune deficiency virus replication in monocytes. Distinctions between restricted and latent expression in THP-1 cells

HIV Latency in Myeloid Cells: Challenges for a Cure

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

HIV replication and latency in monocytes and macrophages

The relevance of monocyte and macrophage reservoirs in virally suppressed people with HIV (vsPWH) has previously been debatable. Macrophages were assumed to have a moderate life span and lack self-renewing potential. However, recent studies have challenged this dogma and now suggest an important role of these cell as long-lived HIV reservoirs. Lentiviruses have a long-documented association with macrophages and abundant evidence exists that macrophages are important target cells for HIV in vivo. A critical understanding of HIV infection, replication, and latency in macrophages is needed in order to determine the appropriate method of measuring and eliminating this cellular reservoir. This review provides a brief discussion of the biology and acute and chronic infection of monocytes and macrophages, with a more substantial focus on replication, latency and measurement of the reservoir in cells of myeloid origin.

Activation of CD35 and CD55 in HIV associated normal and pre-eclamptic pregnant women

OBJECTIVE

The delicate balance which exists between complement activation and its regulation is altered in HIV infection and pregnancy disorders such as pre-eclampsia. Therefore, the purpose of this study was to investigate the expression of complement regulatory (Creg) proteins (CD35 and CD55) in HIV associated normal and pre-eclamptic pregnancies.

STUDY DESIGN

The total study population (n=100) consisted of normotensive pregnant (n=50) and pre-eclamptic (n=50) women. These groups were equally sub-stratified into HIV infected and uninfected groups (n=25 per group). Standard haematological tests were conducted. Flow cytometric analysis of isolated neutrophils were performed using fluorescein isothiocyanate-conjugated anti-CD35 and phycoerythrin-cyanine 5 conjugated anti-CD55.

RESULTS

HELLP syndrome characteristics of increased lactate dehydrogenase enzymes levels, low platelet counts, cell morphological abnormalities (red cell fragmentation) and anaemia were observed in 40% of the HIV infected pre-eclamptic group. Red cell fragmentation inclusive of burr cells and schistocytes were also noted. Activated partial thromboplastin time and fibrinogen differed significantly between the HIV uninfected pre-eclamptic compared to the HIV infected pre-eclamptic groups (p<0.01). Irrespective of HIV status, the mean fluorescence intensity of CD35 and CD55 were significantly higher in the pre-eclamptic compared to the normotensive pregnant (p=0.0001; p=0.0001 respectively) groups. In the pre-eclamptic groups, the expression of both CD35 and CD55 did not significantly differ between HIV infected and uninfected women (p=0.486; p=0.767 respectively).

CONCLUSIONS

This study demonstrates an up-regulation of complement regulatory proteins, CD35 and CD55 in HIV associated pre-eclamptic compared to normotensive pregnancy. This elevation of the Creg proteins is an adaptive immune response to the high complement-mediated cell lysis that occurs in HIV infection and further aggravated by the complement activated state of pre-eclampsia.

Uptake of tenofovir and emtricitabine into non-monocytic female genital tract cells with and without hormonal contraceptives

Background

Pre-exposure prophylaxis is becoming a strategic component used to control the human immunodeficiency virus (HIV-1) epidemic. The goal of this study was to characterize intracellular uptake of tenofovir and emtricitabine using five surrogate cell lines of the female genital tract and determine whether exogenous hormones influence their uptake.

Methods

Surrogate cell lines, ie, THP-1 (representing macrophages), BC-3 (CD8+), Ect1/E6E7 (squamous epithelial), HeLa (CD4+), and TF-1 (dendritic), were incubated for one hour with tenofovir and emtricitabine to assess uptake. In separate experiments, ethinyl estradiol (EE) and etonogestrel (ET) individually and together (EE/ET) were added prior to, simultaneously, and after incubation. Intracellular phosphorylated tenofovir and emtricitabine were quantified using validated tandem mass spectrometry methods.

Results

HeLa and Ect1/E6E7 cells showed significantly increased uptake relative to THP-1 controls for both antiretrovirals. Individually, ethinyl estradiol and etonogestrel significantly altered antiretroviral uptake across all cell lines, except Ect1/E6E7 for tenofovir and HeLa for emtricitabine. Cellular uptake of tenofovir and emtricitabine in BC-3 and TF-1 cells were significantly lower when dosed one hour prior to EE/ET administration compared with each antiretroviral administered in the absence of EE/ET (tenofovir, 80 versus 470 fmol/10⁶ for BC-3 and 77 versus 506 fmol/10⁶ cells for TF-1; emtricitabine, 36 versus 12 fmol/10⁶ for BC-3 and 75 versus 5 fmol/10⁶ cells for TF-1; P < 0.01 for each).

Conclusion

These data suggest that intracellular uptake of tenofovir and emtricitabine within the female genital tract varies by cell type and in the presence of hormonal contraceptives. The potential clinical implications of these findings should be further evaluated in vivo.

Regulation of HIV-1 transcription in cells of the monocyte-macrophage lineage

Human immunodeficiency virus type 1 (HIV-1) has been shown to replicate productively in cells of the monocyte-macrophage lineage, although replication occurs to a lesser extent than in infected T cells. As cells of the monocyte-macrophage lineage become differentiated and activated and subsequently travel to a variety of end organs, they become a source of infectious virus and secreted viral proteins and cellular products that likely initiate pathological consequences in a number of organ systems. During this process, alterations in a number of signaling pathways, including the level and functional properties of many cellular transcription factors, alter the course of HIV-1 long terminal repeat (LTR)-directed gene expression. This process ultimately results in events that contribute to the pathogenesis of HIV-1 infection. First, increased transcription leads to the upregulation of infectious virus production, and the increased production of viral proteins (gp120, Tat, Nef, and Vpr), which have additional activities as extracellular proteins. Increased viral production and the presence of toxic proteins lead to enhanced deregulation of cellular functions increasing the production of toxic cellular proteins and metabolites and the resulting organ-specific pathologic consequences such as neuroAIDS. This article reviews the structural and functional features of the cis-acting elements upstream and downstream of the transcriptional start site in the retroviral LTR. It also includes a discussion of the regulation of the retroviral LTR in the monocyte-macrophage lineage during virus infection of the bone marrow, the peripheral blood, the lymphoid tissues, and end organs such as the brain. The impact of genetic variation on LTR-directed transcription during the course of retrovirus disease is also reviewed.

HIV induces both a down-regulation of IRAK-4 that impairs TLR signalling and an up-regulation of the antibiotic peptide dermcidin in monocytic cells

HIV-infected individuals have an increased risk of invasive bacterial infections, even at early clinical stages with relatively normal CD4(+) T-cell counts. The pathogenic mechanisms behind this are not fully understood. However, an increasing number of studies indicate that HIV may impair the innate immunity to bacteria by infecting key cells of the monocyte/macrophage lineage. In this study, the effects of HIV infection on the protein profile of undifferentiated monocyte-like THP-1 cells were examined by a mass spectrometric approach based on stable isotope labelling with amino acid in cell culture (SILAC). We identified 651 proteins, of which nine proteins were down-regulated and 17 proteins were up-regulated in HIV-infected THP-1 cells as compared to uninfected controls. Most remarkably, the IL-1 receptor associated kinase 4 (IRAK-4), which is essential for virtually all TLR signalling, was suppressed, whereas the precursor for the antibiotic peptide Dermcidin was up-regulated in HIV-infected cells. Upon stimulation of either TLR2 or TLR4, the HIV-infected THP-1 cells displayed reduced TNF-alpha secretion. The HIV-induced down-regulation of IRAK-4 was reconfirmed in monocyte-derived macrophage cell cultures. These data suggests that HIV may impair the TLR signalling cascade for pathogen recognition in cells of the monocyte/macrophage lineage and thus, may reduce the ability of the innate immune system to sense invading pathogens and initiate appropriate responses.

Activation of human monocytes after infection by human coronavirus 229E

Human coronaviruses (HCoV) are recognized respiratory pathogens that may be involved in other pathologies such as central nervous system (CNS) diseases. To investigate whether leukocytes could participate in respiratory pathologies and serve as vector for viral spread towards other tissues, the susceptibility of human leukocytic cell lines and peripheral blood mononuclear cells (PBMC) to HCoV-229E and HCoV-OC43 infection was investigated. Human primary monocytes/macrophages were susceptible to HCoV-229E infection, but strongly restricted HCoV-OC43 replication. Moreover, productive HCoV-229E infection of primary monocytes and of the THP-1 monocytic cell line led to their activation, as indicated by the production of pro-inflammatory mediators, including TNF-alpha, CCL5, CXCL10 and CXCL11 and MMP-9. Moreover, an in vitro chemotaxis assay showed that motility towards chemokines of THP-1 cells and primary monocytes was increased following an acute or persistent HCoV-229E infection. Taken together, these results suggest that infected monocytes could serve as a reservoir for HCoV-229E, become activated, participate in the exacerbation of pulmonary pathologies, as well as serve as potential vectors for viral dissemination to host tissues, where it could be associated with other pathologies.

p73 gene promoter methylation in Epstein-Barr virus-associated gastric carcinoma

To clarify the significance of p73 in Epstein-Barr virus (EBV)-associated gastric carcinoma (GC), the immunohistochemical expression and CpG-island methylation of p73 were evaluated in cancer tissues and adjacent nonneoplastic tissues of GC with and without EBV infection. Loss of p73 expression by immunohistochemistry was specific to EBV-associated GC (11/13) compared to EBV-negative GC (3/38), which was independent of abnormal p53 expression. With methylation-specific polymerase chain reaction (MSP), the aberrant methylation of p73 exon 1 was similarly specific to EBV-associated GC (12/13), and also rare in EBV-negative GC (2/38). Bisulfite sequencing for p73 exon 1 and its 5' region confirmed the MSP results, showing uniform and high-density methylation in EBV-associated GC. Comparative MSP analysis of p14, p16 and p73 methylation, using 20 cases each of formalin-fixed and paraffin-embedded tissues of early GC with and without EBV infection, confirmed 2 types of methylation: global methylation with increased rates (p14 and p16) and specific methylation of p73 in EBV-associated GC. In nonneoplastic mucosa, p14, p16 and p73 methylation occurred in both EBV-associated (8/33, 6/34 and 3/38, respectively) and EBV-negative GC (6/23, 4/35, and 1/35). p73 methylation was observed in the mucosa without H. pylori infection in all 4 samples. Loss of p73 expression through aberrant methylation of the p73 promoter occurs specifically in EBV-associated GC, together with the global methylation of p14 and p16. A specific type of gastritis, prone to a higher grade of atrophy and p73 methylation, may facilitate the development of EBV-associated GC.

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.

Infection of CD4+ primary T cells and cell lines, generation of chronically infected cell lines, and induction of HIV expression

Acute infection of most primary cells and cell lines with HIV depends upon the sequential engagement of CD4 (primary receptor) and a chemokine coreceptor (usually CCR5 or CXCR4) by gp120 Env. Chronically infected cell lines and clones are currently used as sources of virus for infecting other cell types, as "factories" for large-scale production of virions or viral components, and as model systems for studies of regulation of virus expression. This unit provides detailed protocols for acute in vitro HIV infection of primary T cell blasts, interleukin-2-stimulated PBMC, and resting PBMC. The unit also contains information on how to determine the chemokine coreceptor usage of the virus for experimental infections. The use of cell lines as targets of acute infection is also described. Finally, protocols for generating and studying chronically HIV-infected cell lines are provided.

Statins Could Be Used to Control Replication of Some Viruses, Including HIV-1

Statins are mainly known for their plasma cholesterol-lowering properties and are widely used for the prevention of cardiovascular diseases. They however also exert pleiotropic effects through a variety of mechanisms, among which several immunosuppressive effects that are unrelated to their cholesterol-lowering activity. Interestingly, there has been recent evidence of antiviral effects, including preliminary studies on the efficacy of statins against HIV-1. This paper more particularly focuses on the specific inhibition of the binding of leukocyte function-associated antigen-1 (LFA-1) to intercellular adhesion molecule (ICAM-1) by statins, independently of the inhibition of HMGCoA reductase. Targeting the statin-binding site within LFA-1 or regulating LFA-1 affinity by inhibiting prenylation of the small GTPases could prove useful to treat inflammatory, autoimmune diseases and possibly viral infections, including HIV-1.

Transcriptional suppression of in vitro-integrated human immunodeficiency virus type 1 does not correlate with proviral DNA methylation

Persistence of human immunodeficiency virus type 1 (HIV-1) constitutes a major obstacle in the control of HIV-1 infection. Here we investigated whether the CpG methylation of the HIV-1 promoter can directly influence the expression of the HIV-1 genome and thereby contribute to the persistence and latency of HIV-1. The levels of CpG methylation in the promoter of HIV-1 were studied after bisulfite-induced modification of DNA in five Jurkat clonal cell lines transduced by an HIV-1 long terminal repeat (LTR)-driven retroviral vector and expressing enhanced green fluorescent protein (GFP) and in primary resting memory T cells challenged with HIV-1 or with an HIV-1-derived retroviral vector. Basal HIV-1 promoter activities were low or undetectable in three tested HIV-1 LTR-GFP clones, one of which encoded the Tat protein, and they reached medium or high levels in two other clones. The CpG dinucleotide that occurred in a latently infected clonal cell line 240 nucleotides upstream of the transcription start remained methylated after reactivation of HIV-1 transcription with 10 nM phorbol-12-myristate-13-acetate. In two clones showing a medium promoter activity and in resting memory T cells, the HIV-1 LTR was generally not methylated. Our results show that the methylation profiles of the HIV-1 LTR, including those present in latently infected cells, are low and do not correlate with the transcriptional activity. We suggest that, in a noncloned cellular population in which the HIV-1 proviruses are randomly integrated in the human genome, HIV-1 latency is imperfectly controlled by CpG methylation and is inherently accompanied by residual replication.

Global and non-random CpG-island methylation in gastric carcinoma associated with Epstein-Barr virus

DNA hypermethylation may play a primary role in the genesis of Epstein-Barr virus (EBV)-associated gastric carcinoma (GC) (EBVaGC). Methylation-specific PCR targeting CpG-islands demonstrated markedly increased methylation of specific genes, such as p14, p15 and p16 genes, in EBVaGC in vivo. A high frequency of methylation was observed in an EBVaGC strain of severe combined immunodeficiency mice, and the expression of methylated genes in the strain was apparently lower than the expression of the unmethylated genes in EBV-negative GC strains. Although over-expression of DNA methyltransferases (DNMTs) is known to be associated with some human cancers, real-time PCR demonstrated that DNMTs expression was suppressed in EBVaGC. The DNA methylation of specific genes, independently of DNMTs expression, may be important in the development of EBVaGC.

DNA methylation in cancer: too much, but also too little

Cancer-associated DNA hypomethylation is as prevalent as cancer-linked hypermethylation, but these two types of epigenetic abnormalities usually seem to affect different DNA sequences. Much more of the genome is generally subject to undermethylation rather than overmethylation. Genomic hypermethylation in cancer has been observed most often in CpG islands in gene regions. In contrast, very frequent hypomethylation is seen in both highly and moderately repeated DNA sequences in cancer, including heterochromatic DNA repeats, dispersed retrotransposons, and endogenous retroviral elements. Also, unique sequences, including transcription control sequences, are often subject to cancer-associated undermethylation. The high frequency of cancer-linked DNA hypomethylation, the nature of the affected sequences, and the absence of associations with DNA hypermethylation are consistent with an independent role for DNA undermethylation in cancer formation or tumor progression. Increased karyotypic instability and activation of tumor-promoting genes by cis or trans effects, that might include altered heterochromatin-euchromatin interactions, may be important consequences of DNA hypomethylation which favor oncogenesis. The relationship of DNA hypomethylation to tumorigenesis is important to be considered in the light of cancer therapies involving decreasing DNA methylation. Inducing DNA hypomethylation may have short-term anticancer effects, but might also help speed tumor progression from cancer cells surviving the DNA demethylation chemotherapy.

Secretory leukocyte protease inhibitor: inhibition of human immunodeficiency virus-1 infection of monocytic THP-1 cells by a newly cloned protein

The ability of the salivary protein, secretory leukocyte protease inhibitor (SLPI), to inhibit human immunodeficiency virus-1 (HIV-1) infection in vitro has been reported previously and has led to the suggestion that SLPI may be partially responsible for the low oral transmission rate of HIV-1. However, results contradictory to these findings have also been published. These discrepancies can be attributed to a number of factors ranging from the variability of macrophage susceptibility to HIV infection to the quality of commercially available preparations of SLPI. To resolve these differences and to study further the potential anti-HIV-1 activity of SLPI, the purified and re-folded protein, expressed from a synthetic gene, was examined using human monocytic THP-1 cells. This newly cloned SLPI reduced HIV-1(Ba-L) infection in differentiated THP-1 cells, in contrast to the results observed when using commercially available preparations of SLPI. Interestingly, while the two proteins displayed different anti-HIV effects they had comparable anti-protease activity. The identification of the THP-1 cell line as a system that supports HIV replication, which can be inhibited by a preparation of SLPI now available in large quantities, sets the stage for a thorough investigation of the molecular and structural basis for the anti-HIV activity of SLPI.

Expression of CD4 controls the susceptibility of THP-1 cells to infection by R5 and X4 HIV type 1 isolates

The monocytic THP-1 cell line has been used to study HIV-monocyte/macrophage interactions and the relationship between differentiation, virus production, and virus latency. Undifferentiated THP-1 cells are susceptible to infection by T-tropic human immunodeficiency virus type 1 (HIV-1) isolates that use the coreceptor CXCR4 (X4 strains). Treatment with phorbol 12-myristate 13-acetate (PMA) induces differentiation of THP-1 cells into adherent macrophage-like cells, which are susceptible to M-tropic, CCR5-dependent isolates (R5 strains). The aim of this study was to determine whether variabilities observed in the susceptibility of THP-1 cells to HIV-1 infection may be related to the differential expression of CD4, CCR5, and CXCR4. Both propagation and PMA treatment of THP-1 cells resulted in a marked decrease in CD4-positive cells, whereas the expression of CCR5 and CXCR4 was not reduced during propagation. Both coreceptors were also relatively "resistant" to PMA-induced downregulation when compared with the low percentage of CD4-positive cells in differentiated cultures. In undifferentiated THP-1 cells, low CD4 expression significantly reduced the susceptibility of the cells to infection with the R5 HIV-1(BaL) isolate, whereas a PMA-induced decrease in CD4 expression reduced permissiveness of the cells to the X4 HIV-1(IIIB) isolate. Thus, cell surface CD4 plays a primary role in determining how efficiently THP-1 cells can be infected with the X4 and the R5 isolates.

Infection of lymphoid cells by integration-defective human immunodeficiency virus type 1 increases de novo methylation

DNA methylation, by regulating the transcription of genes, is a major modifier of the eukaryotic genome. DNA methyltransferases (DNMTs) are responsible for both maintenance and de novo methylation. We have reported that human immunodeficiency virus type 1 (HIV-1) infection increases DNMT1 expression and de novo methylation of genes such as the gamma interferon gene in CD4(+) cells. Here, we examined the mechanism(s) by which HIV-1 infection increases the cellular capacity to methylate genes. While the RNAs and proteins of all three DNMTs (1, 3a, and 3b) were detected in Hut 78 lymphoid cells, only the expression of DNMT1 was significantly increased 3 to 5 days postinfection. This increase was observed with either wild-type HIV-1 or an integrase (IN) mutant, which renders HIV replication defective, due to the inability of the provirus to integrate into the host genome. Unintegrated viral DNA is a common feature of many retroviral infections and is thought to play a role in pathogenesis. These results indicate another mechanism by which unintegrated viral DNA affects the host. In addition to the increase in overall genomic methylation, hypermethylation and reduced expression of the p16(INK4A) gene, one of the most commonly altered genes in human cancer, were seen in cells infected with both wild-type and IN-defective HIV-1. Thus, infection of lymphoid cells with integration-defective HIV-1 can increase the methylation of CpG islands in the promoters of genes such as the p16(INK4A) gene, silencing their expression.

Therapeutic targeting of human immunodeficiency virus type-1 latency: current clinical realities and future scientific possibilities

Factors affecting HIV-1 latency present formidable obstacles for therapeutic intervention. As these obstacles have become a clinical reality, even with the use of potent anti-retroviral regimens, the need for novel therapeutic strategies specifically targeting HIV-1 latency is evident. However, therapeutic targeting of HIV-1 latency requires an understanding of the mechanisms regulating viral quiescence and activation. These mechanisms have been partially delineated using chronically infected cell models and, clearly, HIV-1 activation from latency involves several key viral and cellular components. Among these distinctive therapeutic targets, cellular factors involved in HIV-1 transcription especially warrant further consideration for rational drug design. Exploring the scientific possibilities of new therapies targeting HIV-1 latency may hold new promise of eventual HIV-1 eradication.

Chimeric retroviral helper virus and picornavirus IRES sequence to eliminate DNA methylation for improved retroviral packaging cells

Most retroviral packaging cell lines were established by a helper virus plasmid cotransfected with a separate plasmid encoding a selection marker. Since this selection marker coexisted in trans with the helper virus sequence, helper virus gene expression could be inactivated by host DNA methylation despite selection for the cotransfected selection marker. We have reported that DNA methylation could occur in the long terminal repeat (LTR) region of helper virus in vector producer cells (VPC) in up to 2% of the population per day (W. B. Young, G. L. Lindberg, and C. J. Link, Jr., J. Virol. 74:3177-3187, 2000). To overcome host cell DNA methylation that suppresses viral gene expression, we constructed a chimeric retroviral helper virus, pAM3-IRES-Zeo, that contains Moloney murine leukemia virus as a helper virus and a picornavirus internal ribosome entry site (IRES) sequence followed by a Zeocin selection marker at the 3' end of the env sequence. This pAM3-IRES-Zeo permitted selection for intact and functional helper virus in transfected cells without subcloning. By selection with Zeocin, a mixed population of pAM3-IRES-Zeo-transfected NIH3T3 cells (AMIZ cells) was maintained with little or no DNA methylation of the helper virus 5' LTR. The high level of pAM3-IRES-Zeo gene expression resulted in no detectable vector superinfection and in high vector titers (2 x 10(6) to 1.5 x 10(7) CFU/ml) after introduction of a retroviral vector. When Zeocin selection was withdrawn from AMIZ cells, methylation of the 5' LTR increased from 17 to 36% of the population during 67 days of continuous culture and the cells became susceptible to superinfection. During this period, gene expression of pAM3-IRES-Zeo decreased and vector titer production was reduced to 2 x 10(4) CFU/ml. These data demonstrate an important role of DNA methylation in the genetic instability of VPC. The chimeric helper virus allows the establishment of a mixed population of packaging cells capable of high-level and sustained vector production without cloning procedures.

Laureate ESCI award for excellence in clinical science 1999. Cytokines and the human immunodeficiency virus: from bench to bedside. European Society for Clinical Investigation

Replication of the human immunodeficiency virus (HIV), the causative agent of the acquired immunodeficiency syndrome (AIDS), is under the control of both viral and host factors. Among the latter, the regulatory network of cytokines has been shown to affect virtually every step of the virus life cycle, from cell entry to budding of new progeny virions. Proinflammatory cytokines, such as tumour necrosis factor alpha, can either trigger or potentiate HIV expression via activation of the cellular transcription factor NF-kappaB. Other molecules, including interleukin 6 (IL-6) and the interferons, can up-regulate HIV expression by acting predominantly at post-transcriptional and/or post-translational levels. Anti-inflammatory cytokines, including transforming growth factor beta, IL-4 and IL-10, counteract these effects but can also potentiate viral replication under different experimental conditions. Chemotactic cytokines (chemokines) have recently entered the arena of host factors controlling viral spreading as potent inhibitors competing with the virus for cell-surface 7-transmembrane domain receptors also acting, together with CD4, as entry co-receptors for HIV. The cytokine network is constitutively activated in most HIV-infected individuals, as demonstrated by recent analysis of intracellular signalling molecules such as the Janus kinase/signal transducer and activator of transcription pathway. Finally, cytokines have already shown their potential use as pharmacological agents able to restore at least some of the compromised immune functions in infected individuals, as exemplified by the potent enhancing effect of IL-2 on the number of circulating CD4+ T lymphocytes.

Interaction of cationic liposomes and their DNA complexes with monocytic leukemia cells

Cationic liposomes complexed with DNA have been used extensively as non-viral vectors for the intracellular delivery of reporter or therapeutic genes in culture and in vivo. We examined the relationship between the characteristics of the lipoplexes, their mode of interaction with monocytic THP-1 cells and their ability to transfect these cells. We determined the size and zeta potential of cationic liposomes (composed of 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP) and its mixtures with neutral lipids), and lipoplexes at different (+/-) charge ratios. As the (+/-) charge ratio of the lipoplexes decreased to (1/1), a significant reduction in zeta potential and an increase in size was observed. The increase in size resulted from fusion between liposomes promoted by DNA, as demonstrated by a lipid mixing assay, and from aggregation of the complexes. Interaction of liposomes and lipoplexes with THP-1 cells was assessed by monitoring lipid mixing ('fusion') as well as binding and cell association. While no lipid mixing was observed with the 1/2 (+/-) lipid/DNA complexes, lipoplexes with higher (+/-) charge ratios underwent significant fusion in conjunction with extensive cell binding. Liposome binding to cells was dependent on the positive charge of the liposomes, and their fusion could be modulated by the co-lipid. DOTAP/phosphatidylethanolamine (1:1) liposomes fused with THP-1 cells, unlike DOTAP/phosphatidylcholine (1:1) liposomes, although both liposome types bound to the cells to a similar extent. The use of inhibitors of endocytosis indicated that fusion of the cationic liposomes with cells occurred mainly at the plasma membrane level. The presence of serum increased the size of the cationic liposomes, but not that of the lipoplexes. Low concentrations of serum (3%) completely inhibited the fusion of cationic liposomes with cells, while inhibiting binding by only 20%. Our results suggest that binding of cationic liposomes and lipoplexes to cells is governed primarily by electrostatic interactions, whereas their fusion is regulated by the lipid composition and sterically favorable interactions with cell surface molecules. In addition our results indicate no correlation between fusion of the lipoplexes with the plasma membrane and the levels of transfection.

Infection with human immunodeficiency virus type 1 upregulates DNA methyltransferase, resulting in de novo methylation of the gamma interferon (IFN-gamma) promoter and subsequent downregulation of IFN-gamma production

The immune response to pathogens is regulated by a delicate balance of cytokines. The dysregulation of cytokine gene expression, including interleukin-12, tumor necrosis factor alpha, and gamma interferon (IFN-gamma), following human retrovirus infection is well documented. One process by which such gene expression may be modulated is altered DNA methylation. In subsets of T-helper cells, the expression of IFN-gamma, a cytokine important to the immune response to viral infection, is regulated in part by DNA methylation such that mRNA expression inversely correlates with the methylation status of the promoter. Of the many possible genes whose methylation status could be affected by viral infection, we examined the IFN-gamma gene as a candidate. We show here that acute infection of cells with human immunodeficiency virus type 1 (HIV-1) results in (i) increased DNA methyltransferase expression and activity, (ii) an overall increase in methylation of DNA in infected cells, and (iii) the de novo methylation of a CpG dinucleotide in the IFN-gamma gene promoter, resulting in the subsequent downregulation of expression of this cytokine. The introduction of an antisense methyltransferase construct into lymphoid cells resulted in markedly decreased methyltransferase expression, hypomethylation throughout the IFN-gamma gene, and increased IFN-gamma production, demonstrating a direct link between methyltransferase and IFN-gamma gene expression. The ability of increased DNA methyltransferase activity to downregulate the expression of genes like the IFN-gamma gene may be one of the mechanisms for dysfunction of T cells in HIV-1-infected individuals.

Similar levels of human immunodeficiency virus type 1 replication in human TH1 and TH2 clones

Studies on the development and function of CD4+ TH1 and TH2 cells during the progression to AIDS may increase the understanding of AIDS pathogenesis. The preferential replication of human immunodeficiency virus (HIV) in either TH1 or TH2 cells could alter the delicate balance of the immune response. TH1 (gamma interferon [IFN-gamma] positive, interleukin-4 [IL-4] and IL-5 negative) and TH2 (IFN-gamma negative, IL-4 and IL-5 positive) clones, developed from several healthy donors, pedigreed by reverse transcriptase PCR (RT-PCR) and enzyme linked immunosorbent assay have similar levels of cell surface expression of CD4 and several chemokine receptor cofactors necessary for viral entry. After activation by specific antigens and infection with T-cell-tropic strains of HIV type 1 (HIV-1), TH1 and TH2 clones showed similar levels of viral entry and reverse transcription. At days 3 through 14 postinfection, HIV replicated to similar levels in several TH1 and TH2 clones as measured by release of HIV p24 and total number of copies of gag RNA/total cell RNA as measured by RT-PCR. When values were normalized for viable cell number in three clones of each type, there was up to twofold more HIV RNA in TH1 than TH2 cells. In addition, several primary monocytotropic HIV-1 strains were able to replicate to similar levels in TH1 and TH2 cells. These studies suggest that the importance of TH1 and TH2 subsets in AIDS pathogenesis transcends clonal differences in their ability to support HIV replication.

Transduction of the human immunodeficiency virus type 1 promoter into human chromosomal DNA by adeno-associated virus: effects on promoter activity

Transcription of the human immunodeficiency virus type 1 (HIV-1) genome takes place after integration of the provirus into human chromosomal DNA. HIV transcription is known to be modulated by viral and cellular factors but the influence of flanking chromosomal sequences on proviral gene expression has not been well defined. To investigate the activity of the integrated HIV promoter, we exploited the ability of recombinant adeno-associated virus (AAV-2) to transfer and stably integrate genes into the human genome at random or site-specifically. Chimeric AAV vectors were constructed containing an HIV-CAT reporter cassette; some vectors also contained the neomycin resistance gene to facilitate the isolation of positive clones. HeLa cells were infected with recombinant AAV, in some instances together with wild-type virus as a source of AAV rep function. We isolated 25 clones of G418-resistant cells which carried the integrated HIV-CAT cassette, generally occupying unique sites that did not correspond to the AAV-specific region of chromosome 19. The HIV promoter was transcriptionally active in most of the clones. Basal promoter activity varied substantially among the clones, and its responsivity to the HIV transactivator Tat was also variable. The integrated HIV promoter was transactivated to comparable degrees by the one-exon form and two-exon form of Tat. These findings provide evidence that the transcriptional activity of the HIV promoter can be greatly influenced by the site of proviral insertion.

Human immunodeficiency virus type-1 (HIV-1) infection increases the sensitivity of macrophages and THP-1 cells to cytotoxicity by cationic liposomes

Cationic liposomes may be valuable for the delivery of anti-sense oligonucleotides, ribozymes, and therapeutic genes into human immunodeficiency virus type 1 (HIV-1)-infected and uninfected cells. We evaluated the toxicity of three cationic liposomal preparations, Lipofectamine, Lipofectin, and 1, 2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide (DMRIE) reagent, to HIV-infected and uninfected cells. Monocyte/macrophages were infected with HIV-1BaL and treated with liposomes in medium containing 20% fetal bovine serum (FBS) for 4 h or 24 h at 37 degree C. Uninfected monocytic THP-1 cells and chronically infected THP-1/HIV-1IIIB cells were treated with phorbol 12-myristate 13-acetate (PMA) and exposed to liposomes in the presence of 10% FBS. Toxicity was evaluated by the Alamar Blue assay and viral p24 production. The toxic effect of cationic liposomes was very limited with uninfected cells, although concentrations of liposomes that were not toxic within a few days of treatment could cause toxicity at later times. In HIV-1BaL-infected macrophages, Lipofectamine (up to 8 microM) and Lipofectin (up to 40 microM) were not toxic after a 4-h treatment, while DMRIE reagent at 40 microM was toxic. While a 4-h treatment of THP-1/HIV-1IIIB cells with the cationic liposomes was not toxic, even up to 14 days post-treatment, all three cationic liposomes were toxic to cells at the highest concentration tested after a 24-h treatment. Similar results were obtained with the Alamar Blue assay, Trypan Blue exclusion and a method that enumerates nuclei. Infected cells with relatively high overall viability could be impaired in their ability to produce virions, indicating that virus production appears to be more sensitive to treatment with the cationic liposomes than cell viability. Our results indicate that HIV-infected cells are more susceptible than uninfected cells to killing by cationic liposomes. The molecular basis of this differential effect is unknown; it is proposed that alterations in cellular membranes during virus budding cause enhanced interactions between cationic liposomes and cellular membranes.

A nuclear matrix-specific factor that binds a specific segment of the negative regulatory element (NRE) of HIV-1 LTR and inhibits NF-kappa(B) activity

The negative regulatory element (NRE) of human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR) is a defined region that has been reported to downregulate LTR-directed HIV gene expression. However, information on the precise role of this region in regulating HIV gone transcription is lacking. We have investigated the possibility that these NRE sequences regulate HIV transcription by a mechanism mediated through a nuclear matrix-specific DNA-protein interaction. We find a nuclear matrix attachment region (MAR) present within the NRE of the HIV-1 LTR that recognizes a sequence-specific DNA-binding protein present in the nuclear matrix of HIV infected cells. Moreover, we also show that the purified DNA-binding nuclear matrix protein (NMP) specifically represses the DNA-binding activity of NF-kappaB. It is likely that the MAR and MAR-enriched specific DNA-binding NMP are brought into juxtaposition by the non-chromatin scaffolding of the nucleus, thus influencing NF-kappaB (and other nuclear proteins) DNA-binding activity through protein-protein and protein-DNA interactions. Our date suggest that one possible role of the NRE could be to act as a matrix attachment site in the nuclear matrix, thus, allowing interaction with a sequence-specific trans-acting factor. The negative effect on NF-kappaB activity due to this MAR-NMP-specific interaction provides a mechanism by which the NRE downregulates HIV gene expression.

In vitro infection of primary and retrovirus-infected human leukocytes by human foamy virus

The infectivity of human foamy virus (HFV) was examined in primary and cultured human leukocytes. Cell-free infectious viral stocks of HFV were prepared from the human kidney cell line 293 transfected with an infectious molecular clone of HFV. HFV productively infects a variety of human myeloid and lymphoid cell lines. In addition, primary cell cultures enriched for human CD4+, monocytes and brain-derived microglial cells, were readily infected by HFV. Interestingly, while infected primary CD4+ lymphocytes and microglial cells showed marked cytopathology characteristic of foamy virus, HFV-infected monocyte-derived macrophages failed to show any cytopathology. In addition, marked cytotoxicity due to HFV infection was seen in both human T-cell leukemia virus type 1- and human immunodeficiency virus type 1-infected T-cell lines and in human immunodeficiency virus type 1-infected monocytoid cell lines. Thus, HFV infection produces differential cytopathology in a wide host range of primary human leukocytes and hematopoietic cell lines.

Role of IgE immune complexes in the regulation of HIV-1 replication and increased cell death of infected U1 monocytes: involvement of CD23/Fc epsilon RII-mediated nitric oxide and cyclic AMP pathways

BACKGROUND

IgE/anti-IgE immune complexes (IgE-IC) induce the release of multiple mediators from monocytes/macrophages and the monocytic cell line U937 following the ligation of the low-affinity Fc epsilon receptors (Fc epsilon RII/CD23). These effects are mediated through an accumulation of cAMP and the generation of L-arginine-dependent nitric oxide (NO). Since high IgE levels predict more rapid progression to acquired immunodeficiency syndrome, we attempted to define the effects of IgE-IC on human immunodeficiency virus (HIV) production in monocytes.

MATERIALS AND METHODS

Two variants of HIV-1 chronically infected monocytic U1 cells were stimulated with IgE-IC and virus replication was quantified. NO and cAMP involvement was tested through the use of agonistic and antagonistic chemicals of these two pathways.

RESULTS

IgE-IC induced p24 production by U1 cells with low-level constitutive expression of HIV-1 mRNAs and extracellular HIV capsid protein p24 levels (U1low), upon their pretreatment with interleukin 4 (IL-4) or IL-13. This effect was due to the crosslinking of CD23, as it was reversed by blocking the IgE binding site on CD23. The IgE-IC effect could also be mimicked by crosslinking of CD23 by a specific monoclonal antibody. p24 induction by IgE-IC was then shown to be due to CD23-mediated stimulation of cAMP, NO, and tumor necrosis factor alpha (TNF alpha) generation. In another variant of U1 cells with > 1 log higher constitutive production of p24 levels (U1high), IgE-IC addition dramatically decreased all cell functions tested and accelerated cell death. This phenomenon was reversed by blocking the nitric oxide generation.

CONCLUSIONS

These data point out a regulatory role of IgE-IC on HIV-1 production in monocytic cells, through CD23-mediated stimulation of cAMP and NO pathways. IgE-IC can also stimulate increased cell death in high HIV producing cells through the NO pathway.

Restriction of human immunodeficiency virus type 1 production in a human astrocytoma cell line is associated with a cellular block in Rev function

Chronically human immunodeficiency virus type 1 (HIV-1) strain IIIB-infected human TH4-7-5 astrocytoma cells show low-level virus production. Cocultivation of TH4-7-5 cells with myelomonocytic cells led to active virus production in these target cells after a lag period, indicating cell-determined restriction of virus replication in the glial cells. HIV-1 transcript patterns of TH4-7-5 cells contained only a small proportion of Rev-dependent mRNA species, mimicking a Rev-negative phenotype despite the presence of rev mRNAs and protein. Sequencing of the single provirus integrated in TH4-7-5 cells demonstrated that the rev gene and the Rev-responsive element are intact. These results suggested inhibited function of the Rev-regulatory unit in these astrocytoma cells. Transfection of TH4-7-5 cells with a Rev expression plasmid resulted in weak or no induction of proviral p24gag antigen levels compared with the dramatic increase observed in Rev-permissive HeLa cells. Immunofluorescence analysis of TH4-7-5 cells transfected with a rev-expressing plasmid revealed prominent cytoplasmic and nuclear-nucleolar localization of Rev, in contrast to the predominant nuclear-nucleolar localization pattern of Rev in HeLa cells. We conclude that restriction of virus production in TH4-7-5 cells is at least partially due to a block in Rev-dependent posttranscriptional regulation of HIV expression.

Regulation of I kappa B alpha and p105 in monocytes and macrophages persistently infected with human immunodeficiency virus

The mechanisms regulating human immunodeficiency virus (HIV) persistence in human monocytes/macrophages are partially understood. Persistent HIV infection of U937 monocytic cells results in NF-kappa B activation. Whether virus-induced NF-kappa B activation is a mechanism that favors continuous viral replication in macrophages remains unknown. To further delineate the molecular mechanisms involved in the activation of NF-kappa B in HIV-infected monocytes and macrophages, we have focused on the regulation of the I kappa B molecules. First, we show that persistent HIV infection results in the activation of NF-kappa B not only in monocytic cells but also in macrophages. In HIV-infected cells, I kappa B alpha protein levels are decreased secondary to enhanced protein degradation. This parallels the increased I kappa B alpha synthesis secondary to increased I kappa B alpha gene transcription, i.e., increased RNA and transcriptional activity of its promoter-enhancer. Another protein with I kappa B function, p105, is also modified in HIV-infected cells: p105 and p50 steady-state protein levels are increased as a result of increased synthesis and proteolytic processing of p105. Transcriptional activity of p105 is also increased in infected cells and is also mediated by NF-kappa B through a specific kappa B motif. These results demonstrate the existence of a triple autoregulatory loop in monocytes and macrophages involving HIV, p105 and p50, and MAD3, with the end result of persistent NF-kappa B activation and viral persistence. Furthermore, persistent HIV infection of monocytes and macrophages provides a useful model with which to study concomitant modifications of different I kappa B molecules.

Anti-human immunodeficiency virus 1 (HIV-1) activities of 3-deazaadenosine analogs: increased potency against 3'-azido-3'-deoxythymidine-resistant HIV-1 strains

3-Deazaadenosine (DZA), 3-deaza-(+/-)-aristeromycin (DZAri), and 3-deazaneplanocin A (DZNep) are powerful modulators of cellular processes. When tested against H9 cells infected acutely with two different strains of human immunodeficiency virus 1 (HIV-1) and in the chronically infected monocytoid cell lines U1 and THP-1, the 3-deazanucleosides caused a marked reduction in p24 antigen production. Similar reductions in p24 antigen were seen in phytohemagglutinin-stimulated peripheral blood mononuclear cells infected with clinical HIV-1 isolates. Strikingly, in comparing the therapeutic indices between the paired pre- and post-3'-azido-3'-deoxythymidine (AZT) treatment HIV-1 isolates, DZNep and neplanocin A showed an increase of 3- to 18-fold in their potency against AZT-resistant HIV-1 isolates. In H9 cells treated with DZNep and DZAri, the formation of triphosphate nucleotides of DZNep and DZAri was observed. The mode of action of DZNep and DZAri appears complex, at least in part, at the level of infectivity as shown by decreases in syncytia formation in HIV-1-infected H9 cells and at the level of transcription as both drugs inhibited the expression of basal or tat-induced HIV-1 long terminal repeat chloramphenicol acetyltransferase activity in stably transfected cell lines. Since DZNep induced in H9 cells a rapid expression of nuclear binding factors that recognize the AP-1 transcription site, the anti-HIV-1 activity of the DZA analogs could partly be the induction of critical factors in the host cells. Thus, the 3-deazanucleoside drugs belong to an unusual class of anti-HIV-1 drugs, which may have therapeutic potential, in particular against AZT-resistant strains.

A family of serine proteases expressed exclusively in myelo-monocytic cells specifically processes the nuclear factor-kappa B subunit p65 in vitro and may impair human immunodeficiency virus replication in these cells

Two groups of U937 promonocytic cells were obtained by limiting dilution cloning which differed strikingly in their ability to support human immunodeficiency virus 1 (HIV-1) replication. "Plus" clones replicated the virus efficiently, whereas "minus" clones did not. We examined these clones for differences in nuclear factor (NF)-kappa B activity which might account for the observed phenomenon. Stimulation of plus clones liberated the classical p50-p65 complex from cytoplasmic pools, whereas minus clones produced an apparently novel, faster-migrating complex, as judged by electrophoretic mobility shift assays. It is surprising that the faster-migrating complex was composed also of p50 and p65. However, the p65 subunit was COOH-terminally truncated, as shown by immunoprecipitation. The truncation resulted from limited proteolysis of p65 during cellular extraction which released particular lysosomal serine proteases, such as elastase, cathepsin G, and proteinase 3. These specific proteases are coordinately expressed and were present exclusively in the minus U937 clones, but not in the plus clones, as demonstrated in the case of cathepsin G. In addition, these proteases were detected in certain subclones of THP-1 and HL-60 cells and in primary monocytes, in each case correlating with the truncated from of p65. We demonstrate in vitro cleavage of p65 by purified elastase and cathepsin G. It is possible that particular serine proteases may have inhibiting effects on the replication of HIV-1 in myelo-monocytic cells. The data also demonstrate that special precautions must be taken when making extracts from myelo-monocytic cells.

Association of alterations in NF-kappa B moieties with HIV type 1 proviral latency in certain monocytic cells

Human immunodeficiency virus type 1 (HIV-1) replication is controlled by a complex array of virally encoded and cellular proteins. A wide spectrum of levels of HIV-1 expression have been demonstrated in various cells, both in cell culture and in vivo. Molecular mechanisms leading to restricted HIV-1 replication may differ between certain cell types. It is now demonstrated that HIV-1 proviral latency in the monocytic cell line U1, in which only extremely low levels of HIV-1 expression are detected in the baseline unstimulated state, is associated with alterations in nuclear factor-kappa B (NF-kappa B) moieties demonstrated in these cells by electrophoretic mobility shift assays (EMSAs) and in situ UV cross-linking studies. A predominance of p50 NF-kappa B moieties and possibly p50 homodimers or closely related species, rather than the p50-p56 heterodimer of NF-kappa B that is the predominant NF-kappa B species in most T lymphocytic and monocytic cells, is demonstrated in the nuclei of U1 cells. This pattern of NF-kappa B-related moieties differs from the latently infected T lymphocytic cell line ACH-2, and from the U937 monocytic line, the parental cell line of the U1 cellular clone. As such, these data suggest that different proximal mechanisms may lead to restricted HIV-1 replication in various cell types.

The NF-kappa B binding site is necessary for efficient replication of simian immunodeficiency virus of macaques in primary macrophages but not in T cells in vitro

We demonstrate here that the nuclear factor-kappa B (NF-kappa B) binding site in the simian immunodeficiency virus (SIVmac) long terminal repeat is essential for efficient virus replication in primary alveolar macrophages but dispensable for efficient replication in primary T cells. Mutation of the NF-kappa B site does not seriously impair replication of a T-cell-tropic SIVmac239 or a macrophagetropic SIVmacEm* in peripheral blood lymphocytes or established CD4+ cell lines; however, mutation of the NF-kappa B site prevents efficient SIVmacEm* replication in primary alveolar macrophages. These data suggest that efficient replication in primary macrophages requires both envelope and long terminal repeat determinants.

CR1 (CD35) and CR3 (CD11b/CD18) mediate infection of human monocytes and monocytic cell lines with complement-opsonized HIV independently of CD4

Peripheral blood and tissue mononuclear phagocytes serve as major viral reservoirs in HIV-infected individuals. We investigated the role of complement receptors CR1 (CD35) and CR3 (CD11b/CD18) in mediating productive infection with complement-opsonized HIV-1 and HIV-2 of cultured normal human peripheral blood monocytes, the promonocytic cell line THP-1, the monocytic cell line Mono Mac 6 and the glial cell line U251-MG. Cells were infected with the HTLV-IIIB strain of HIV-1 or the LAV-2 strain of HIV-2 that had been preopsonized with fresh human normal HIV seronegative serum. Productive infection was assessed by syncytia formation, the MTT cytotoxicity assay and/or release of p24 antigen in culture supernatants. Using suboptimal amounts of virus to infect the cells, we observed a higher and earlier productive infection of the cells with complement-opsonized HIV than with unopsonized virus. The enhancing effect of complement was totally suppressed by blocking CR1 or CR3 function with F(ab)'2 fragments of anti-receptor MoAbs; while blocking of the LFA-1 antigen had no effect. The infection of monocytic cells with complement-opsonized virus occurred independently of CD4 since it was not inhibited by F(ab)'2 fragments of a MoAb against the gp120 binding site of CD4 and since infection also occurred with Mono Mac 6 and U251-MG cells, which lack expression of the CD4 antigen and of CD4 mRNA. These observations suggest that complement may mediate productive infection of cells of the monocytic lineage with 'lymphocytotropic' HIV strains independently of CD4.

Human T-cell leukemia virus type I infection of monocytes and microglial cells in primary human cultures

The pathogenesis of progressive spastic paraparesis [HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP)], a serious consequence of human T-cell leukemia virus type I (HTLV-I) infection, is unclear. T and B lymphocytes can be naturally infected by HTLV-I, but the susceptibility to HTLV-I infection of other cell types that could contribute to the pathogenesis of HAM/TSP has not been determined. We found that a human monocyte cell line (THP-1), primary human peripheral blood monocytes, and isolated microglial cells but not astrocytes or oligodendroglial cells derived from adult human brain were infected by HTLV-I in vitro. Infection with HTLV-I enhanced the secretion of interleukin 6 in human microglial cell-enriched cultures but did not stimulate the release of interleukin 1 from monocytes or microglial cells. Tumor necrosis factor alpha production was stimulated by HTLV-I infection of monocytes and microglial cells and could be enhanced by suboptimal amounts of lipopolysaccharide. Since both tumor necrosis factor alpha and interleukin 6 have been implicated in inflammatory demyelination and gliosis, our findings suggest that human microglial cells and monocytes infected with and activated by HTLV-I could play a role in the pathogenesis of HAM/TSP.

Activation of infectious virus from latent human immunodeficiency virus infection of monocytes in vivo

Individuals infected with HIV may be asymptomatic for years before progressing to overt AIDS. Since HIV can latently infect monocytoid cell lines, we examined whether HIV latency occurs in monocytes in vivo. Freshly isolated monocytes from asymptomatic seropositive individuals examined before and after culture were positive for HIV DNA, but not RNA, as measured by polymerase chain reaction, showing that HIV latency occurs in monocytes in vivo. Coculture of these latently infected monocytes with Con A-activated T cells from HIV-negative normal donors stimulated 90% of the patients' samples and latently infected THP-1 to produce infectious virus. Neither Con A, resting T cells, nor T cell supernatants induced virus. Plasma membranes from activated T cells stimulated HIV production, suggesting cell contact induces factor(s) in monocytes to overcome latency. Thus, monocytes in AIDS patients harbor latent HIV inducible during an immune response, leading to T cell infection and viral-induced pathology.

The nef gene of simian immunodeficiency virus SIVmac1A11

The role of the simian immunodeficiency virus (SIV) nef gene in viral replication was investigated in several tissue culture systems. SIVmac1A11 is a molecularly cloned virus which replicates in both peripheral blood mononuclear cells (PBMC) and macrophages, although no disease is observed in infected rhesus macaques. In this report, we demonstrate that SIVmac1A11 contains a full open reading frame for nef which specifies a 37-kDa protein. To investigate the effects of nef on viral replication, a 70-bp deletion was introduced into the nef gene of SIVmac1A11. Analysis of infected cell extracts by immunoblotting revealed that both SIVmac1A11 and nef deletion virus SIVmac1A11 delta nef produced the same viral proteins, except that Nef was absent in the mutant virus. The deletion mutation did not affect viral replication in PBMC, in monocyte-derived and alveolar macrophages obtained from rhesus macaques, and in human cell lines HUT-78 and CEMx-174. In addition, SIVmac1A11 and SIVmac1A11 delta nef exhibited similar patterns of cytopathologic changes and ultrastructural appearances in infected cells. SIVmac1A11 and SIVmac1A11 delta nef did not infect human tumor macrophage cell line U937, GCT, THP-1, or HL-60 cells, although virus was produced after these cells were transfected with either wild-type or nef mutant viral DNA. Similar levels of virus were recovered from U937 and THP-1 cells transfected with mutant and parental proviral DNAs. In transient expression assays in a T-cell line and a macrophage line, the nef protein of SIVmac1A11 did not significantly suppress or enhance expression of the chloramphenicol acetyltransferase reporter gene linked to the SIVmac long terminal repeat. Thus, abrogation of nef did not affect several in vitro properties of SIVmac1A11, including patterns of viral infection in rhesus PBMC, rhesus macrophages, or human T-cell lines.

Cellular latency of human immunodeficiency virus type 1

The infection of humans by human immunodeficiency virus type 1 is characterized by a prolonged stage of clinical quiescence. This clinically asymptomatic period may be based, in part, on the development of cell populations within the body that maintain human immunodeficiency virus type 1 in a state of latency. Recent advances in the understanding of the molecular mechanisms involved in various forms of cellular latency of human immunodeficiency virus type 1 have begun to shed light on the variable period of asymptomatic infection. The elucidation of cellular retroviral latency, in vivo, will also be critical to the design of novel therapeutic approaches with which to combat human immunodeficiency virus type 1 infections.

Application of latent HIV-1 infected cellular models to therapeutic intervention

The 10-year period of clinical latency following infection with the human immunodeficiency virus type-1 remains as a tremendous opportunity for therapeutic intervention. To decipher the viral and cellular mechanisms involved in controlling active and nonproductive viral expression, chronically infected cell lines have been developed which mimic in vivo latency at a cellular level. This review compares these models of chronic infection, emphasizing the advantages and limitations of this approach to the understanding of AIDS progression. In addition, it accentuates the utility of these models of chronic infection in the development and testing of novel drugs aimed at altering the efferent component of the HIV--1 life cycle. It is this component of the viral life cycle that has remained largely unexplored and open to novel therapeutic strategies for the prevention of lethal immunosuppression.

Negative regulation of human immunodeficiency virus type 1 expression in monocytes: role of the 65-kDa plus 50-kDa NF-kappa B dimer

Although monocytic cells can provide a reservoir for viral production in vivo, their regulation of human immunodeficiency virus type 1 (HIV-1) transcription can be either latent, restricted, or productive. These differences in gene expression have not been molecularly defined. In THP-1 cells with restricted HIV expression, there is an absence of DNA-protein binding complex formation with the HIV-1 promoter-enhancer associated with markedly less viral RNA production. This absence of binding was localized to the NF-kappa B region of the HIV-1 enhancer; the 65-kDa plus 50-kDa NF-kappa B heterodimer was preferentially lost. Adding purified NF-kappa B protein to nuclear extracts from cells with restricted expression overcomes this lack of binding. In addition, treatment of these nuclear extracts with sodium deoxycholate restored their ability to form the heterodimer, suggesting the presence of an inhibitor of NF-kappa B activity. Furthermore, treatment of nuclear extracts from these cells that had restricted expression with lipopolysaccharide increased viral production and NF-kappa B activity. Antiserum specific for NF-kappa B binding proteins, but not c-rel-specific antiserum, disrupted heterodimer complex formation. Thus, both NF-kappa B-binding complexes are needed for optimal viral transcription. Binding of the 65-kDa plus 50-kDa heterodimer to the HIV-1 enhancer can be negatively regulated in monocytes, providing one mechanism restricting HIV-1 gene expression.

Inhibition of human immunodeficiency virus replication in acutely infected CD4+ cells by CD8+ cells involves a noncytotoxic mechanism

The mechanism by which CD8+ T cells from human immunodeficiency virus (HIV)-infected individuals suppress HIV replication in acutely infected CD4+ T cells was investigated. Cytotoxicity was not involved, as the antiviral activity of the CD8+ cells did not correlate with the ability to lyse HIV-infected or uninfected CD4+ T cells. In addition, the frequency of HIV-infected CD4+ cells increased during coculture with CD8+ T cells even in the absence of detectable levels of virus replication. Moreover, separation of the CD4+ and CD8+ cells by a 0.4-micron-pore-size filter delayed HIV replication, indicating a role, at least in part, for a soluble factor. However, cell contact was required for optimal antiviral activity. These results extend further the observation on the mechanism of antiviral HIV activity by CD8+ cells from infected individuals. They support the conclusion that CD8+ cells can play a major role in preventing development of disease in HIV-infected individuals.

Activation of human monocyte--derived macrophages with lipopolysaccharide decreases human immunodeficiency virus replication in vitro at the level of gene expression

Activation of T lymphocytes infected with the human immunodeficiency virus-1 (HIV-1) results in enhancement of viral replication mediated in part by activation of cellular NF kappa B capable of binding directly to sequences in the viral long terminal repeat, or LTR. Together with CD4+ T cells, macrophages constitute a major target for infection by HIV-1. Unlike lymphocytes, however, stimulation of mononuclear phagocytes is not associated with cell division and proliferation. Human monocyte-derived macrophages transfected with HIV-LTR-CAT constructs demonstrated down-regulation of CAT activity after stimulation with bacterial lipopolysaccharide (LPS) that mapped to a region distinct from NF kappa B binding sites. In contrast, fresh monocytes and the promonocytic U937 cell line both demonstrated up-regulation of HIV-LTR-CAT expression by LPS. Differentiation of U937 by PMA to establish a nondividing phenotype resulted in down-regulation of transfected HIV-LTR-CAT activity by LPS similar to that in mature macrophages. Human monocyte-derived macrophages infected with HIV-1 in vitro demonstrated a decrease in viral p24 release after incubation in LPS that was comparable to the negative regulation that occurred in the transient transfection assays. Factors controlling HIV replication may differ in dividing and nondividing hematopoietic cells and may contribute to restricted viral expression in nondividing cells.