Human cytomegalovirus infection induces transcription and secretion of transforming growth factor beta 1

Human cytomegalovirus (CMV) infection can elicit a transitory, but profound, immunodepression in immunocompetent individuals. Cytopathogenic destruction of CMV-infected leukocytes alone does not seem sufficient to explain this phenomenon, which suggests that immune system mediators (cytokines) may play a role in amplifying local modifications wrought by CMV infection. We reported previously that transforming growth factor beta 1 (TGF-beta 1) stimulates CMV replication (J. Alcami, C. V. Paya, J. L. Virelizier, and S. Michelson, J. Gen. Virol. 74:269-274, 1993). Since TGF-beta 1 can have profound negative effects on cell growth and immune responses, we investigated the induction of TGF-beta 1 following CMV infection of permissive fibroblasts. TGF-beta 1 promoter was activated by immediate-early (IE) proteins in the absence of infection and transactivated at 5 and 9 h after infection. TGF-beta 1 mRNA increased during the early phase of infection, suggesting that this phenomenon is due to enhanced transcription of the TGF-beta 1 gene. A comparative study of the influence of CMV infection and IE protein expression on TGF-beta 1 promoter function in permissive cells pointed to a possible cooperative role between IE proteins and protein(s) expressed during the early phase of viral infection. Induction of TGF-beta 1 by CMV infection could modify infected cells individually, surrounding tissues, and systemic immune reactions to the advantage of virus replication by both upregulating CMV replication and downregulating host immune responses.

Appraisal of potential therapeutic index of antioxidants on the basis of their in vitro effects on HIV replication in monocytes and interleukin 2-induced lymphocyte proliferation

Antioxidant molecules have been suggested to be of therapeutic value in the treatment of HIV-infected patients. To evaluate this possibility, we examined in vitro the effects of two types of antioxidant molecules in terms of inhibition of HIV replication in monocytes, one of the main reservoirs of HIV, and also in terms of modulation of the immune competence as measured by PBMC proliferation. We tested the effects of BHA, a phenolic, lipid-soluble, chain-breaking antioxidant, and NAC, a known glutathione precursor with some direct free-radical scavenging properties as well, on the regulation of HIV-1 expression in latently infected U1 cells and in productively and chronically infected U937 cells. Both antioxidants inhibited TNF- or PMA-induced NF-kappa B activity in U1 cells, as well as the sustained NF-kappa B activity permanently induced by the virus itself in chronically HIV-infected U937 cells. This resulted in only a partial inhibition of TNF- or PMA-induced HIV replication in U1 cells, and no detectable effect on HIV replication in chronically infected U937 cells. This may be the first limitation to potential antiviral effects of antioxidant therapies. Another limitation is that antioxidant concentrations high enough to block NK-kappa B activation were shown to have a suppressive effect on immune functions in vitro, because NAC and BHA blocked IL-2-induced PBMC proliferation. These data warrant prudence in the design of antioxidant-based therapies aimed at suppressing HIV replication.

Phosphatidylcholine hydrolysis activates NF-kappa B and increases human immunodeficiency virus replication in human monocytes and T lymphocytes

We have tested whether breakdown of phosphatidylcholine (PC) initiated by exogenous addition of a PC-specific phospholipase C (PC-PLC) from Bacillus cereus or by endogenous overexpression of PC-PLC induces functional activation of NF-kappa B and increases human immunodeficiency virus (HIV) enhancer activity. PC-PLC-activated hydrolysis of PC was found to induce bona fide p50/p65 NF-kappa B binding activity in three different cell lines of human or murine origin. No significant changes in the turnover of other cellular phospholipids were detected in PC-PLC-treated cells. Induction of NF-kappa B by PC-PLC did not depend on de novo synthesis of proteins or autocrine secretion of either tumor necrosis factor or interleukin 1. In human monocytic and lymphoblastoid T-cell lines, induction of NF-kappa B by PC-PLC resulted in clear induction of luciferase expression vectors placed under the control of synthetic kappa B enhancers or wild type, but not kappa B-mutated, HIV long terminal repeat constructs. HIV replication was increased by PC-PLC in chronically infected monocytes and T lymphocytes. NF-kappa B activation promoted by addition of exogenous PC-PLC correlated with an intense production of diacylglycerol. However, addition of a phosphatidylinositol-specific PLC from B. cereus also induced diacylglycerol but did not activate kappa B enhancer-directed vectors. PC-PLC-induced NF-kappa B activation could not be blocked by a specific inhibitor of phorbol ester-inducible protein kinases C. These results indicate that a cellular transduction pathway, dependent on specific PC breakdown, is functional in T lymphocytes and monocytes and may be used by various transmembrane receptors to activate HIV transcription through NF-kappa B-dependent induction of the HIV enhancer.

A dominant negative protein kinase C zeta subspecies blocks NF-kappa B activation

Nuclear factor kappa B (NF-kappa B) plays a critical role in the regulation of a number of genes. NF-kappa B is a heterodimer of 50- and 65-kDa subunits sequestered in the cytoplasm complexed to inhibitory protein I kappa B. Following stimulation of cells, I kappa B dissociates from NF-kappa B, allowing its translocation to the nucleus, where it carries out the transactivation function. The precise mechanism controlling NF-kappa B activation and the involvement of members of the protein kinase C (PKC) family of isotypes have previously been investigated. It was found that phorbol myristate acetate, (PMA) which is a potent stimulant of phorbol ester-sensitive PKC isotypes, activates NF-kappa B. However, the role of PMA-sensitive PKCs in vivo is not as apparent. It has recently been demonstrated in the model system of Xenopus laevis oocytes that the PMA-insensitive PKC isotype, zeta PKC, is a required step in the activation of NF-kappa B in response to ras p21. We demonstrate here that overexpression of zeta PKC is by itself sufficient to stimulate a permanent translocation of functionally active NF-kappa B into the nucleus of NIH 3T3 fibroblasts and that transfection of a kinase-defective dominant negative mutant of zeta PKC dramatically inhibits the kappa B-dependent transactivation of a chloramphenicol acetyltransferase reporter plasmid in NIH 3T3 fibroblasts. All these results support the notion that zeta PKC plays a decisive role in NF-kappa B regulation in mammalian cells.

Inhibition of protein kinase C zeta subspecies blocks the activation of an NF-kappa B-like activity in Xenopus laevis oocytes

Nuclear factor kappa B (NF-kappa B) plays a critical role in the regulation of a large variety of cellular genes. However, the mechanism whereby this nuclear factor is activated remains to be determined. In this report, we present evidence that in oocytes from Xenopus laevis, (i) ras p21- and phospholipase C (PLC)-mediated phosphatidylcholine (PC) hydrolysis activates NF-kappa B and (ii) protein kinase C zeta subspecies is involved in the activation of NF-kappa B in response to insulin/ras p21/PC-PLC. Thus, the microinjection of either ras p21 or PC-PLC, or the exposure of oocytes to insulin, promotes a significant translocation to the nucleus of an NF-kappa B-like activity. This effect is not observed when oocytes are incubated with phorbol myristate acetate or progesterone, both of which utilize a ras p21-independent pathway for oocyte activation. These data strongly suggest a critical role of the insulin/ras p21/PC-PLC/protein kinase C zeta pathway in the control of NF-kappa B activation.

Antagonistic modulation of human cytomegalovirus replication by transforming growth factor beta and basic fibroblastic growth factor

We studied the effect of two cytokines, basic fibroblastic growth factor (bFGF) and transforming growth factor beta (TGF-beta) on human cytomegalovirus (HCMV) replication in cultured human lung fibroblasts. We show that TGF-beta increases HCMV production, probably by a transcriptional mechanism, and that bFGF represses HCMV replication in a dose-dependent manner. These actions were antagonistic and the mechanisms involved were independent of the effects of these factors on cell DNA synthesis and proliferation.

Redox status of cells influences constitutive or induced NF-kappa B translocation and HIV long terminal repeat activity in human T and monocytic cell lines

We have tested the hypothesis that cellular activation events occurring in T lymphocytes and monocytes and mediated through translocation of the transcription factor NF-kappa B are dependent upon the constitutive redox status of these cells. We used phenolic, lipid-soluble, chain-breaking antioxidants (butylated hydroxyanisole (BHA), nordihydroquairetic acid, or alpha-tocopherol (vitamin E) to show that peroxyl radical scavenging in unstimulated and PMA- or TNF-stimulated cells blocks the functions depending on NF-kappa B activation. BHA was found to suppress not only PMA- or TNF-induced, but also constitutive, HIV-enhancer activity concomitant to an inhibition of NF-kappa B binding activity in both lymphoblastoid T (J.Jhan) and monocytic (U937) cell lines. This was also true for KBF (p50 homodimer) binding activity in U937 cells. Secretion of TNF, the product of another NF-kappa B-dependent gene, was abolished by BHA in PMA-stimulated U937 cells. The anti-oxidative effect of BHA was accompanied by an increase in thiol, but not glutathione, content in stimulated and unstimulated T cell, whereas TNF stimulation itself barely modified the cellular thiol level. Oxidative stress obtained by the addition of H2O2 to the culture medium of J.Jhan or U937 cells could not by itself induce NF-kappa B activation. These observations suggest that TNF and PMA do not lead to NF-kappa B activation through induction of changes in the cell redox status. Rather, TNF and PMA can exert their effect only if cells are in an appropriate redox status, because prior modification toward reduction with BHA treatment prevents this activation. It appears that a basal redox equilibrium tending toward oxidation is a prerequisite for full activation of transduction pathways regulating the activity of NF-kappa B-dependent genes.

Redox status of cells influences constitutive or induced NF-kappa B translocation and HIV long terminal repeat activity in human T and monocytic cell lines

We have tested the hypothesis that cellular activation events occurring in T lymphocytes and monocytes and mediated through translocation of the transcription factor NF-kappa B are dependent upon the constitutive redox status of these cells. We used phenolic, lipid-soluble, chain-breaking antioxidants (butylated hydroxyanisole (BHA), nordihydroquairetic acid, or alpha-tocopherol (vitamin E) to show that peroxyl radical scavenging in unstimulated and PMA- or TNF-stimulated cells blocks the functions depending on NF-kappa B activation. BHA was found to suppress not only PMA- or TNF-induced, but also constitutive, HIV-enhancer activity concomitant to an inhibition of NF-kappa B binding activity in both lymphoblastoid T (J.Jhan) and monocytic (U937) cell lines. This was also true for KBF (p50 homodimer) binding activity in U937 cells. Secretion of TNF, the product of another NF-kappa B-dependent gene, was abolished by BHA in PMA-stimulated U937 cells. The anti-oxidative effect of BHA was accompanied by an increase in thiol, but not glutathione, content in stimulated and unstimulated T cell, whereas TNF stimulation itself barely modified the cellular thiol level. Oxidative stress obtained by the addition of H2O2 to the culture medium of J.Jhan or U937 cells could not by itself induce NF-kappa B activation. These observations suggest that TNF and PMA do not lead to NF-kappa B activation through induction of changes in the cell redox status. Rather, TNF and PMA can exert their effect only if cells are in an appropriate redox status, because prior modification toward reduction with BHA treatment prevents this activation. It appears that a basal redox equilibrium tending toward oxidation is a prerequisite for full activation of transduction pathways regulating the activity of NF-kappa B-dependent genes.

NF-kappa B-dependent induction of the NF-kappa B p50 subunit gene promoter underlies self-perpetuation of human immunodeficiency virus transcription in monocytic cells

The molecular mechanisms underlying the sustained nuclear translocation of NF-kappa B observed in U937 monocytic cells chronically infected with human immunodeficiency virus (HIV) were studied. The activity of the promoter regulating the synthesis of the p105 precursor of the NF-kappa B p50 subunit was enhanced in these cells. Deletions in this promoter indicated that this upregulation was mediated through the NF-kappa B- but not the AP-1-binding motif, by bona fide p50/p65 heterodimers. Analysis of cytosolic extracts indicated that NF-kappa B levels were increased in HIV-infected cells. In contrast to the transient NF-kappa B activation induced by phorbol ester, the permanent NF-kappa B translocation induced by HIV infection was not dependent on PKC isoenzymes alpha and beta as shown by the use of a specific inhibitor (GF 109203X). These observations indicate that during chronic HIV infection of U937 cells, continuous NF-kappa B (p50/p65) translocation results in p105 promoter upregulation with subsequent cytosolic NF-kappa B accumulation, ready for further translocation. This HIV-mediated mechanism results in a self-perpetuating loop of NF-kappa B production.

Thioredoxin regulates the DNA binding activity of NF-kappa B by reduction of a disulphide bond involving cysteine 62

A role for redox regulation in activation of the NF-kappa B transcription factor was suggested by the observation that DNA binding activity of free protein, but not preformed DNA-protein complex, is inhibited by -SH modifying agents but enhanced by reducing agents. Mutagenesis of conserved cysteine residues in the p50 subunit identified amino acid 62 as being important for DNA binding, as a serine substitution at this position reduces DNA binding affinity, but renders the protein insensitive to -SH modifying agents. DNA binding activity of the wild type protein but not the amino acid 62 mutant was also stimulated by thioredoxin while detection of disulphide cross linked dimers in p50 but not the amino acid 62 mutant suggests that thioredoxin stimulates DNA binding by reduction of a disulphide bond involving cysteine 62. The physiological relevance of these findings was supported by the observation that cotransfection of a plasmid expressing human thioredoxin and an HIV LTR driven reporter construct resulted in an NF-kappa B dependent increase in expression of the reporter gene. Thus modification of p50 by thioredoxin, a gene induced by stimulation of T-lymphocytes in parallel with NF-kappa B translocation, is a likely step in the cascade of events leading to full NF-kappa B activation.

The characterization of the promoter of the gene encoding the p50 subunit of NF-kappa B indicates that it participates in its own regulation

In order to characterize the regulation of the gene encoding the p50 subunit of the transcription factor NF-kappa B, we have isolated a human genomic clone, and sequenced the promoter of this gene. By in situ hybridization we have mapped the gene encoding the p50 subunit of NF-kappa B to the 4q23-4q25 region of the human genome and the H1-H3 region of the murine chromosome 3. The p50 promoter lacks TATA and CAAT elements, but contains NF-kappa B, AP-1 and HIP-1 binding sequence. The kappa B motif binds NF-kappa B, KBF1, and heterodimers of p50 and c-rel, suggesting that the gene is regulated by members of this family. Co-transfection experiments demonstrate that the p50 promoter can be activated by either of the two subunits of NF-kappa B (p50 and p65), and more strongly by the combination of both. The promoter of p50 can be activated by phorbol esters and tumor necrosis factor alpha but not by forskolin and these responses are mediated through the NF-kappa B binding sequence. The involvement of NF-kappa B in the regulation of the p50 gene is also supported by the inhibition of the PMA activation of the promoter by an NF-kappa B transdominant negative mutant, as well as the product of the v-rel oncogene.

Modulation of T-cell activation through protein kinase C- or A-dependent signalling pathways synergistically increases human immunodeficiency virus long terminal repeat induction by cytomegalovirus immediate-early proteins

By using human CD4+ lymphoblastoid T cells transiently cotransfected with human immunodeficiency virus (HIV) and cytomegalovirus (CMV), we tested whether modulation of T-cell activation through the protein kinase C (PKC) or the protein kinase A (PKA) pathway synergized with CMV immediate-early (IE) proteins in HIV long terminal repeat (LTR) transactivation. Stimulation with phorbol myristate acetate, tumor necrosis factor, or cross-linked antibodies to CD3 and CD28 resulted in modest enhancement (two- to fourfold) of the activity of a luciferase expression vector under control of the HIV LTR. Cotransfection of a vector expressing the CMV IE1 and IE2 proteins under the control of their own promoter enhanced HIV LTR activity 16- to 49-fold. Combination of any one of the above stimuli and CMV IE expression amplified HIV LTR activity 99- to 624-fold. Stimulation of PKA-dependent pathways with forskolin, 8-bromo cyclic AMP, or prostaglandin E2 had a minimal effect on HIV LTR activity, whereas such stimuli resulted in synergistic amplification in cells cotransfected with CMV IE (three- to fivefold increases over the effects of CMV IE alone). This synergism was independent of the NF-kappa B binding motifs within the HIV LTR. CMV IE2, but not IE1, protein induced HIV transactivation and synergized with signals modulating T-cell activation. The intense synergism observed was superior to the increase in IE protein expression following PKC activation by phorbol myristate acetate. Treatment of cells with PKC inhibitor GF109203X blocked most of the observed synergism.(ABSTRACT TRUNCATED AT 250 WORDS)

HIV enhancer activity perpetuated by NF-kappa B induction on infection of monocytes

Permissiveness to replication of human immunodeficiency virus (HIV) differs in T lymphocytes and macrophages. In T cells, HIV transcription is poorly detected in vivo. Cloned, normal T lymphocytes show very little, if any, basal activity of the HIV enhancer and low nuclear expression of NF-kappa B, a potent transcriptional activator of the HIV enhancer. In contrast, fixed tissue macrophages express detectable HIV proteins, indicating permanent virus transcription. One explanation for the perpetuation of virus infection in macrophages could be sustained nuclear NF-kappa B expression. However, the U937 monocytic cell line, which is fully permissive to HIV replication, is known to express only low levels of nuclear NF-kappa B. We show here that chronic HIV infection results in both induction of a nuclear factor with antigenic properties indistinguishable from those of NF-kappa B and permanently increased HIV enhancer activity. This phenomenon, which is independent of tumour necrosis factor, is associated with HIV replication, and is thus likely to explain at least in part the perpetuation of HIV infection in monocytes.

Stimulation of a human T-cell clone with anti-CD3 or tumor necrosis factor induces NF-kappa B translocation but not human immunodeficiency virus 1 enhancer-dependent transcription

The expression of transiently transfected expression vectors under the control of the long terminal repeat (LTR) of the human immunodeficiency virus (HIV) or its enhancer sequence and the translocation of the HIV enhancer-binding protein NF-kappa B were analyzed in two human T-cell clones stimulated through their T-cell receptor complex or by tumor necrosis factor or phorbol 12-myristate 13-acetate. We found a dissociation of NF-kappa B translocation from transactivation of either the HIV LTR or the HIV enhancer. Interleukin 2 induced proliferation but not NF-kappa B translocation or LTR transactivation. Phorbol ester or specific antigen recognition induced HIV LTR transactivation, whereas stimulation with tumor necrosis factor or antibody to CD3 did not. The two latter signals were nevertheless able to induce NF-kappa B translocation with a pattern in the band-shift assay indistinguishable from that observed using phorbol ester. Our finding that induction of NF-kappa B by tumor necrosis factor or antibody to CD3 is not sufficient to induce HIV enhancer-dependent transcription in cloned T cells contrasts with results obtained in most lymphoblastoid T-cell lines and indicates that normal T lymphocytes differ from tumoral T cells in terms of requirements for HIV LTR activation. Furthermore, our results suggest that events linked to T-cell activation, in addition to NF-kappa B translocation per se, induce functional interactions of the NF-kappa B complex with the HIV enhancer.

Constitutive expression of human immunodeficiency virus (HIV) nef protein in human astrocytes does not influence basal or induced HIV long terminal repeat activity

Since human immunodeficiency virus (HIV) nef has been suggested to exert regulatory effects on HIV long terminal repeat (LTR) activity, we transiently transfected HIV LTR chloramphenicol acetyltransferase or luciferase expression vectors into a human astrocytoma clone (U-373nef) that constitutively expresses the HIV nef gene. In these cells, basal HIV LTR activity, as well as tumor necrosis factor-induced or tat-driven activity, was similar to that in control cells. Lack of any detectable effect of HIV nef on LTR activity was not the result of mutations in integrated nef DNA, as was shown by polymerase chain reaction. These data suggest that the role of nef in HIV genome transcription does not necessarily involve a direct influence on HIV LTR activity.

A microtransfection method using the luciferase-encoding reporter gene for the assay of human immunodeficiency virus LTR promoter activity

A microtransfection method, using either the DEAE-dextran or the Ca.phosphate procedure has been developed. A plasmid expressing the luciferase-encoding gene under the control of the human immunodeficiency virus (HIV) LTR promoter was constructed. Transfections were performed in 96-well plates, allowing statistical evaluation of the results. This microtransfection method requires the use of 100- to 1000-fold less plasmid and cells than in a conventional chloramphenicol acetyl transferase (CAT) assay. A Luciferase index which takes into account cell viability after transfection has been defined using a semi-automated absorbance assay. A 20-h incubation period post-transfection is sufficient for optimal results. Basal long terminal repeat activity and autologous Tat transactivation were studied in various lymphoid, monocytic and adherent human cell lines. Infection of microtransfected cells by HIV activated luc expression. This assay can thus also be used for rapid detection and quantitation of HIV. Antiviral activities of drugs can be assessed in a two-day test.

Tumor necrosis factor stimulates transcription of HIV-1 in human T lymphocytes, independently and synergistically with mitogens

We have investigated the effect of TNF, a cytokine produced during most immunologic and inflammatory reactions, on HIV genome expression in human T lymphocytes. A CD4+ human T cell line (J.Jhan) was transfected with vectors permitting the expression of the chloramphenicol acetyl transferase (CAT) gene under the control of the long terminal repeat (LTR) of HIV-1. rTNF was found to induce HIV LTR transactivation as intensely as PHA or phorbol esters. PHA enhanced TNF receptor expression in J.Jhan cells and acted synergistically with TNF on HIV LTR induction. TNF was also shown to induce well expression of a whole HIV provirus genome transfected into J.Jhan cells. The use of various CAT constructs carrying fragments of the HIV LTR, combined with bandshift assays, showed that TNF stimulates HIV transcription by acting on the kB-like enhancer element of the LTR through induction and/or activation of an NF-kB-like protein factor. Such findings are compatible with the hypothesis that TNF production participates in the pathogenesis of AIDS by enhancing HIV replication in T lymphocytes.

Tumor necrosis factor stimulates transcription of HIV-1 in human T lymphocytes, independently and synergistically with mitogens

We have investigated the effect of TNF, a cytokine produced during most immunologic and inflammatory reactions, on HIV genome expression in human T lymphocytes. A CD4+ human T cell line (J.Jhan) was transfected with vectors permitting the expression of the chloramphenicol acetyl transferase (CAT) gene under the control of the long terminal repeat (LTR) of HIV-1. rTNF was found to induce HIV LTR transactivation as intensely as PHA or phorbol esters. PHA enhanced TNF receptor expression in J.Jhan cells and acted synergistically with TNF on HIV LTR induction. TNF was also shown to induce well expression of a whole HIV provirus genome transfected into J.Jhan cells. The use of various CAT constructs carrying fragments of the HIV LTR, combined with bandshift assays, showed that TNF stimulates HIV transcription by acting on the kB-like enhancer element of the LTR through induction and/or activation of an NF-kB-like protein factor. Such findings are compatible with the hypothesis that TNF production participates in the pathogenesis of AIDS by enhancing HIV replication in T lymphocytes.

c-Ha-ras transfection induces human immunodeficiency virus (HIV) transcription through the HIV-enhancer in human fibroblasts and astrocytes

Transient transfection of ras expression vectors into human fibroblasts and astrocytes has been used to test the hypothesis that p21 ras, a known membrane signal transductor, may participate in pathways linking cellular activation and human immunodeficiency virus (HIV) reactivation. Expression vectors carrying the chloramphenicol acetyl transferase coding sequence under the control of various fragments of the long terminal repeat (LTR) of HIV were co-transfected with expression vectors of the mutated (val 12) c-Ha-ras gene or of its normal counterpart. Both forms of the ras gene induced transactivation of the HIV-LTR via the two direct repeat sequences which constitute the HIV enhancer. This repeat sequence was shown to be sufficient for ras-induced LTR transactivation. Other LTR sequences tested were not found to be responsive to co-transfected ras expression vectors. Deletion of the TAR sequence impaired the response to tat, but not to ras co-transfection. The mutated ras gene was more efficient than the proto-oncogene in activating the HIV enhancer. Transfection of ras was shown to enhance transcription of a complete provirus DNA clone of HIV-1. Such findings may shed new light on the mechanisms through which cell membrane activation signals result in HIV reactivation.

Cytomegalovirus infection and trans-activation of HIV-1 and HIV-2 LTRs in human astrocytoma cells

Susceptibility of a human astrocytoma cell line to human cytomegalovirus (HCMV) infection was investigated. Infection of U-373MG astrocytoma cells with two strains of HCMV resulted in both production of extracellular, infectious virus and expression of immediate early and early antigens within 18 hours and late antigens after 72 hours of infection. The kinetics of infection in U-373MG cells were the same as in human diploid fibroblasts (MRC-5). Since HCMV and human immunodeficiency virus (HIV) have reportedly been found in astrocytic cells in vivo, we studied the possible interaction between HCMV and HIV long terminal repeat (LTR) elements in this cellular environment. HCMV infection transactivated the LTR of HIV-1 and HIV-2 to similar levels. Interestingly, transfection of these cells with infectious HIV-1 provirus did not result in expression of gag, env, or F proteins detectable by immunofluorescence. However, provirus gene expression was not completely silent, since it transactivated HIV-1 LTR. The level of this transactivation was similar to that seen following cotransfection with a tat expression vector. These results suggest that opportunistic infection with HCMV may reactivate latent HIV genomes in glial cells.

Autocrine secretion of tumor necrosis factor under the influence of interferon-gamma amplifies HLA-DR gene induction in human monocytes

Recombinant interferon-gamma (IFN-gamma) induced HLA-DR gene expression in both U937 and THP-1 human monocytic cell lines, although the former was only very weakly inducible. Combination of recombinant tumor necrosis factor (TNF) and IFN-gamma resulted in a synergistic enhancement of DR mRNA and protein induction in both cell lines. TNF alone increased the constitutive expression of the DR gene in THP-1 cells. In the HLA class II-negative U937 cells, TNF used alone was not able to induce DR gene expression. Such a negative result was not due to a lack of TNF receptor expression in U937 cells, since TNF clearly induced HLA class I and TNF gene expression in this cell line. THP-1, but not U937, cells secreted TNF under the influence of IFN-gamma. Neutralization of TNF by a specific antibody decreased IFN-gamma-induced DR antigen expression in THP-1 cultures. These observations indicate that TNF is not able to directly induce DR gene expression, but rather amplifies ongoing expression of this gene, whether constitutive or induced by IFN-gamma. In the two cell lines tested, the level of DR inducibility under the influence of IFN-gamma used alone depended on a different inducibility of TNF secretion by IFN-gamma. Altogether, our observations indicate that TNF, whether exogenous or endogenously produced under the influence of IFN-gamma, amplifies DR gene expression in monocytes, a phenomenon that may provide to such antigen-presenting cells a selective sensitivity to the DR-inducing effects of IFN-gamma.

Natural killing of fibroblasts infected with low-passage clinical isolates of human cytomegalovirus

Fibroblasts infected with most low-passage clinical isolates of human cytomegalovirus (CMV) were as susceptible to lysis by human natural killer (NK) cells as high passage AD-169-infected fibroblasts. NK lysis occurred despite the absence of detectable CMV-specific late membrane antigen(s) on the majority of the target cells infected with most of the low passage strains. The magnitude of NK lysis of different CMV-infected target cells did not correlate with their ability to induce IFN-alpha. NK cell-mediated lysis of cells infected with low-passage clinical isolates of CMV required both NK cells and HLA-DR+ accessory cells, as previously shown for AD-169-infected target cells.