Interleukin 15-mediated induction of cytotoxic effector cells capable of eliminating Epstein-Barr virus-transformed/immortalized lymphocytes in culture

BACKGROUND

Interleukin 15 (IL-15) activates cytotoxic lymphocytes and drives the expansion of memory T cells. Its role in immune control of virus-transformed cells and other tumor cells remains to be elucidated. We investigated the role of IL-15 in controlling Epstein-Barr virus (EBV)-transformed/immortalized lymphocytes in culture. EBV is a highly potent lymphocyte-transforming and opportunistic oncogenic herpesvirus associated with several human tumors.

METHODS

Peripheral blood mononuclear cells (PBMCs) from healthy donors were infected with EBV and cultured with either IL-15 or IL-15 plus anti-IL-15 antibodies for 3-4 weeks. We monitored EBV-induced transformation by assessing the clearly visible cell clusters by microscopy and analyzing the expression of EBV-encoded latent membrane oncoprotein-1 (LMP-1) and the EBV nuclear antigen (EBNA) complex by immunoblotting and immunofluorescence techniques, respectively. We depleted EBV-infected cultures of PBMCs of specific effector cell populations to investigate the effector cells involved in mediating IL-15 effect.

RESULTS

The presence of IL-15 resulted in the complete elimination of EBV-transformed cells in PBMC cultures. Western blot and immunofluorescence analyses performed 3-4 weeks after infection showed no detectable levels of LMP-1 and EBNA in IL-15-treated EBV-infected cultures, whereas IL-15-untreated EBV-infected cultures and IL-15/anti-IL-15-treated cultures expressed both proteins. IL-15 mediated its anti-EBV effect through early and late response mechanisms, i.e., by first activating natural killer (NK) cells and subsequently inducing cytolytic NK-T cells. The presence of anti-IL-15 neutralizing antibodies abrogated IL-15's effect on both mechanisms.

CONCLUSION

In vitro, IL-15 mediated complete elimination of EBV-infected/transformed lymphocytes via successive activation of NK and NK-T cytotoxic effectors. If these in vitro findings reflect in vivo mechanisms, then IL-15 might be considered for cytokine-based immunotherapy in patients with EBV-associated lymphoproliferative disorders/malignancies.

Modulation of expression of the MHC class I-binding natural killer cell receptors, and NK activity in relation to viral load in HIV-infected/AIDS patients

The natural killer (NK) cells play an important role in viral infections via their spontaneous cytolytic activity against virus-infected cells as well as via secreting a variety of soluble mediators. The MHC class I-binding NK receptors of these cells have emerged as the most important regulators of the effector activities of cytolytic cells (both NK and CTL). We have studied the modulation of NK activity and the expression of NK receptors in HIV-infected/AIDS patients and report here that the NK activities of the patients with the lowest plasma HIV load were minimal and vice versa, suggesting a decrease in this activity following suppression of HIV replication. Interestingly, the NK activity correlated negatively with the peripheral blood CD4+ T-cell counts of these patients. Furthermore, these patients showed decreased percentages of CD56+ cells expressing NK receptors of the immunoglobulin superfamily, whereas the percentages of CD8+ cells expressing these receptors were increased. Moreover, the expression of C-type lectin-like NK receptor-associated invariant molecule CD94 was increased on CD8+ cells in these patients as compared with HIV-seronegative controls. These changes in the expression of NK receptors were also evident within groups of these patients having different viral loads. These results show, for the first time, decreased innate immunity and changes in the expression of NK receptors on cytolytic cells in relation to viral burden in HIV-infected/AIDS patient.

Epstein-Barr Virus and its glycoprotein-350 upregulate IL-6 in human B-lymphocytes via CD21, involving activation of NF-kappaB and different signaling pathways

Epstein-Barr virus (EBV) is a ubiquitous and highly immunotropic gamma herpesvirus that infects more than 90 % of humans worldwide. Its pathogenicity leads to a number of diseases including tumors that result from EBV's ability to readily transform B-lymphocytes and, to a lesser extent, epithelial cells. EBV utilizes CD21/CR2 as its receptor on B cells to initiate the infection process. EBV binds to CR2 through its major envelope glycoprotein-350 (gp350) and is also a remarkable immunomodulating agent. We had previously shown that EBV is capable of modulating the synthesis of a number of cytokines. We now show that while both purified recombinant gp350 (rgp350) and EBV upregulate IL-6 mRNA synthesis in B cells, EBV-induced IL-6 gene activation occurs for a significantly longer period of time (i.e. 12 hours for EBV as compared to 6 hours for rgp350). Moreover, the half-life of EBV-induced IL-6 mRNA was also significantly longer (10 hours) than that of mRNA induced by rgp350 (about 6 hours). Both EBV and gp350 enhance the binding of the NF-kappaB transcription factor, as determined by band-shift and augment NF-kappaB-mediated activation of a CAT reporter plasmid. Furthermore, we demonstrate that while the activation of IL-6 gene expression by gp350 is mediated primarily by the protein kinase C pathway, EBV can mediate its effects through multiple signaling pathways. To our knowledge this is the first report showing that the binding of a herpesvirus envelope glycoprotein to CR2 on human B cells results in the activation of the NF-kappaB transcription factor leading to the upregulation of IL-6 gene expression in these lymphocytes.

Evidence for a correlation between antibody-dependent cellular cytotoxicity-mediating anti-HIV-1 antibodies and prognostic predictors of HIV infection

Using our gp120/41-expressing, NK cell activity-resistant CEM.NKR cell clones as targets in HIV-1-specific antibody-dependent cellular cytotoxicity (ADCC) assays, we demonstrate here that the serum titers of anti-HIV-1 ADCC antibodies bear a significant (P < 0.05) positive correlation with the peripheral blood CD4+ T cell counts and a negative one with the number of copies of HIV-1 RNA in the plasma of HIV-infected individuals. These findings underscore the importance of these antibodies as a protective immune parameter in these infections.

Activated human platelets express Fas-L and induce apoptosis in Fas-positive tumor cells

In addition to their role in hemostasis and thrombosis, platelets are important modulators of immune and inflammatory responses. We provide evidence here that human platelets contain abundant quantities of Fas-L, and upon activation, they express it on their surface as well as release it into medium. This surface-expressed Fas-L is biologically active and can induce apoptosis in Fas-positive human tumor cells. Therefore, activated platelets may represent an important player in Fas/Fas-L-mediated apoptosis.

Thrombin induces apoptosis in human tumor cells

Thrombin is a serine protease that is produced during the coagulation process and plays an essential role for hemostasis, thrombosis and wound healing. It is a potent activator of platelets, induces proliferation of a wide variety of normal and malignant human cells, and enhances their invasiveness and metastatic potential. We studied the effect of thrombin on the proliferation of a wide variety of human tumor cells and report here that, at low concentrations, thrombin induces proliferation of these cells. However, at higher concentrations, thrombin inhibited their proliferation. We show that this inhibition of cell proliferation was due to apoptosis of the tumor cells. The thrombin-mediated apoptosis was inhibited significantly by its specific inhibitor, hirudin. Furthermore, no consistent pattern of induction and/or modulation of p53, p21 and bcl-2 was observed in the thrombin-mediated apoptosis. To our knowledge, this is the first report to describe the pro-apoptotic effects of thrombin on human tumor cells and may have implications for chemotherapy in cancer patients and for the pathogenesis of AIDS as well.

Innate immune response of the human host to exposure with herpes simplex virus type 1: in vitro control of the virus infection by enhanced natural killer activity via interleukin-15 induction

Infections with herpes simplex virus type 1 (HSV-1) in humans and in animal models are accompanied by enhanced natural killer (NK) activity. In vitro, HSV-1 also enhances the NK activity of human peripheral blood mononuclear cells (PBMC). The molecular basis of this enhanced NK activity, however, is not well characterized. We investigated the role of human interleukin-15 (IL-15) in this phenomenon and report here that HSV-1-mediated enhanced NK activity was abrogated by neutralizing antibodies for IL-15 but not for other cytokines (i.e., IL-2, IL-12, gamma interferon [IFN-gamma], tumor necrosis factor alpha, or IFN-alpha). Anti-CD122 antibodies which block signaling through IL-2 receptor beta chain, and therefore neutralize the effects of IL-15 (and IL-2), also abrogated this enhancement. Furthermore, HSV-1 increased the levels of IL-15 mRNA and the production of IL-15 in HSV-1-infected PBMC cultures. The neutralization of IL-15 in cocultures of PBMC with HSV-1-infected cells significantly increased HSV-1 production. These results strongly suggest a role for IL-15 in the HSV-1-mediated in vitro enhancement of NK activity and in the PBMC-mediated suppression of HSV-1 replication.

Binding of the Epstein-Barr virus major envelope glycoprotein gp350 results in the upregulation of the TNF-alpha gene expression in monocytic cells via NF-kappaB involving PKC, PI3-K and tyrosine kinases

Epstein-Barr virus (EBV) is a human herpesvirus that interacts with various immunocompetent cells that carry the EBV receptor (CD21/CR2). EBV binds to CR2 through its major envelope glycoprotein 350 (gp350). Previously we had demonstrated that EBV and other human herpesviruses are capable of modulating cytokine synthesis through the deregulated expression of cytokine genes interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2). Here we show that, in contrast to infectious EBV, purified recombinant gp350 upregulates TNF-alpha gene expression in human monocyte/macrophages (M/M) as well as in a monocytoid cell line, U937. Our results also demonstrate that this increased expression is due to both enhanced transcription and stability of TNF-alpha mRNA in gp350-treated cells. The specificity of this effect is evidenced by the fact that pre-incubation of cells with anti-CR2 monoclonal antibody OKB7, which blocks binding of gp350 to CR2, inhibits the above mentioned effects of gp350. Furthermore, we demonstrate that activation of TNF-alpha by gp350 is mediated by NF-kappaB through signal transduction pathways involving PKC, PI3-K and tyrosine kinases. To our knowledge this is the first report describing the modulation of TNF-alpha gene expression by the EBV-gp350 molecule following its interaction with the viral receptor CR2 on cells of the monocytic lineage.

Analysis and significance of anti-latent membrane protein-1 antibodies in the sera of patients with EBV-associated diseases

Anti-latent membrane protein-1 (LMP-1) is an EBV-encoded type III integral membrane protein with oncogenic potential that is expressed most consistently in various EBV-associated malignancies. Unlike many other EBV proteins, LMP-1 Abs have rarely been demonstrated in EBV-associated disease conditions. We established a high level LMP-1-expressing cell clone and used it for the detection, quantitation, and characterization of these Abs in various human sera in immunoblots and ELISA. Our results demonstrate that, in contrast to the commonly held notion, LMP-1 induces significant humoral immune responses in EBV-associated malignant conditions especially in nasopharyngeal carcinoma (NPC) patients in whom >70% sera are positive for these Abs, and their titers correlate with the clinical condition of the tumors. Interestingly, anti-LMP-1 Abs of IgA isotype were found only in NPC patients. These Abs were absent from the sera of infectious mononucleosis and chronic EBV infection patients, whereas a small fraction ( approximately 5%) of the healthy, EBV-seropositive individuals were positive for them; however, their OD values were much lower than those of NPC patients. These studies demonstrate, for the first time, the potential significance of LMP-1-specific Abs for the diagnosis and prognosis of EBV-associated malignancies, especially of NPC.

Elevated serum transforming growth factor beta1 levels in Epstein-Barr virus-associated diseases and their correlation with virus-specific immunoglobulin A (IgA) and IgM

Transforming growth factor beta (TGF-beta) is an immunosuppressive cytokine which can induce immunoglobulin A (IgA) switch and Epstein-Barr virus (EBV) replication in latently infected cells. Here we report elevated serum levels of TGF-beta in various EBV-associated diseases correlating positively with EBV-specific IgA titers and negatively with IgM titers, suggesting a role for this cytokine in the pathogenesis of these diseases.

Epstein-Barr virus envelope glycoprotein gp350 induces NF-kappaB activation and IL-1beta synthesis in human monocytes-macrophages involving PKC and PI3-K

Epstein-Barr virus (EBV) is a highly immunotropic human herpesvirus with oncogenic potential and is involved in numerous pathologies. EBV utilizes its major envelope glycoprotein gp350 to bind to its receptor CR2/CD21 on target cells for initiating the infection. We have previously shown that EBV is able to modulate transcription and translation of a number of cytokine genes via its gp350-mediated binding to this receptor. However, the effects of the binding of purified gp350 to CR2/CD21 on plastic-adherent monocyte-macrophages (AMM) have not been investigated. These cells are a rich source of potent proinflammatory and immune-modulating cytokines, and express low levels of CR2/CD21. We show here for the first time that recombinant gp350 (rgp350) causes production of the potent proinflammatory cytokine IL-1beta in human AMM. Surprisingly, rgp350 is comparable in this capacity to the phorbol ester 12-0-tetradecanoylphorbol 13-acetate. This induction of IL-1beta production was accompanied by increased steady-state levels of its mRNA in gp350-treated AMM, and was dependent on the specific binding of rgp350 to the EBV receptor CR2/CD21. We also show that the signaling pathways resulting in the induction of IL-1beta synthesis by rgp350 required protein kinase C and phosphatidylinositol 3,4,5 triphosphate kinase activities and occurred via activation of the NF-kappaB family of transcription factors.-D'Addario, M., Ahmad, A., Xu, J. W., Menezes, J. Epstein-Barr virus envelope glycoprotein gp350 induces NF-kappaB activation and IL-1beta synthesis in human monocytes-macrophages involving PKC and PI3-K.

Modulatory effects of human herpes virus-7 on cytokine synthesis and cell proliferation in human peripheral blood mononuclear cell cultures

Human herpes virus-7 (HHV-7) infects cells of the immune system and thus may modulate their function. To investigate the potential immunomodulatory effects of this virus, we performed an in vitro study in which we investigated effects of HHV-7 on the synthesis of several key immunomodulatory cytokines, i.e. tumor necrosis factor alpha (TNF-alpha), interleukin-2 (IL-2), interferon-gamma (IFN-gamma), IL-4, IL-6, and transforming growth factor beta (TGF-beta). This was examined after in vitro infection of human peripheral blood mononuclear cells (PBMC) with HHV-7. We found elevated levels of TNF-alpha, TGF-beta, and IFN-gamma in the supernatants of HHV-7-infected cells. By reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, using cytokine-specific primers, we found that levels of TNF-alpha, TGF-beta, and IFN-gamma mRNA were increased in the infected cells. The HHV-7 infection also significantly (P < 0.05) decreased the production of IL-2 from activated, IL-2-producing PBMC. Furthermore, mitogen- and cytokine-induced cellular proliferative responses of human PBMC were found to be significantly (P < 0.05) down-regulated by this virus. On the other hand, HHV-7 did not affect IL-4 and IL-6 synthesis. Overall, our results indicate that HHV-7 infection causes significant immunomodulatory effects with regard to cytokine synthesis in these cells as well as inhibiting lymphocyte proliferation by various stimuli.

Up-regulation of NK cytotoxic activity via IL-15 induction by different viruses: a comparative study

IL-15 is a recently identified cytokine that belongs to the four alpha-helix bundle cytokine family and possesses biological activities similar to those of IL-2. Its ability to induce effectors of NK activity suggests its involvement in innate immunity. In this study, we analyzed the effect of different viruses (HSV, EBV, respiratory syncitial virus, vesicular stomatitis virus, influenza virus, reovirus, and Sendai virus) on the up-regulation of NK activity in vitro. Exposure of human PBMC to the these viruses resulted in an immediate up-regulation of NK activity of PBMC via IL-15 induction; this effect was abrogated in the presence of mAbs to IL-15. Results of experiments conducted in parallel using mAbs to IL-15, as well as to other cytokines (IL-2, IL-12, IFN-gamma, and TNF-alpha), clearly indicated that IL-15 was specifically responsible for the observed effect. Furthermore, supernatants of virus-infected PBMC cultures significantly enhanced NK activity of uninfected PBMC in vitro. An increase of IL-15 protein levels 20 h postinfection was also confirmed in a bioassay using the IL-2-dependent cell line CTLL. Kinetic analysis of IL-15 mRNA expression using a semiquantitative RT-PCR revealed that the level of IL-15 messages peaked at different time points (up to 12 h) postinfection, depending on the nature of the virus. Taken together, these results suggest that the IL-15 response of the host to viral infection and the subsequent NK cell activation represent an important effector mechanism of the innate immune surveillance of the host against viral infections.

[In vitro cytokine induction in leukocytes by human herpesvirus 7]

Virus infections of the immune system may alter the normal cytokine profile, which leads to symptoms of illnesses. HHV-7 revealed lately has been known as one of the causative agents of exanthem subitum and pityriasis rosea, while its latent infection can be reactivated in immunocompromised conditions. Their pathomechanism has not been explored yet, therefore, the production of some cytokines by separated leukocytes was studied upon primary and secondary infections. After combined treatments with live or inactivated viruses and/or mitogens, the cytokines were quantitated in the supernatant of cells by sandwich ELISA. It was established that, individual cytokines were produced at maximal output at different times postinfection. The quantity of their molecules depended on the primary or repeated infections. Inactivated viral particles also induced cytokine release. Production of IL-2 and IFN-gamma due to mitogen activation could be augmented in primary, but was diminished in secondary infections. Release of TNF-alpha and IL-1 beta was parallel, but the combinatory effect with mitogens increased the quantity of IL-1 beta. HHV-7 induced early IL-10 production, which is known to inhibit cytokine release from helper lymphocytes and consequently might play a role in those acute inflammatory skin diseases mentioned above. In contrast to the related HHV-6 found in severe immunosuppressed conditions, the effect of HHV-7 on the balanced production of different cytokines seems to be related to the mild symptoms of skin disorders caused and that of moderate immunosuppression upon reactivation.

Elevated serum levels of transforming growth factor beta1 in Epstein-Barr virus-associated nasopharyngeal carcinoma patients

Nasopharyngeal carcinomas (NPCs) of non-keratinizing type are strongly associated with Epstein-Barr virus (EBV). EBV and its gene products induce the synthesis and/or release of transforming growth factor beta1 (TGF-beta1) from human cells and platelets. TGF-beta1 is an immunosuppressive cytokine, and many tumors are known to secrete it, to counter the host immune response. To determine the potential role of this cytokine in the pathogenesis of NPC, 53 serum samples from patients with EBV-associated NPC and 20 from healthy donors were analyzed for total and active TGF-beta content using ELISA. Serum samples for TGF-beta content were also analyzed from NPC patients at different clinical stages of the tumors. Significantly higher (p < 0.01) levels of active and total TGF-beta were found in the sera of NPC patients than in control sera. The ratio of active:total TGF-beta was also significantly (p < 0.01) increased in the NPC sera. Levels of this cytokine were also significantly higher (p < 0.05) in the sera of patients with advanced stages of tumor compared to patients with earlier stages. Furthermore, higher levels were seen in patients with relapsing than with remitting tumors; even higher levels were observed in NPC patients who died of the tumor. Our data suggest a role of this cytokine in the pathogenesis of NPC; therefore, it may prove to be a valuable biomarker molecule for the diagnosis and prognosis of NPC. Int. J. Cancer (Pred. Oncol.) 84:396-399, 1999.

A novel nitric oxide scavenger decreases liver injury and improves survival after hemorrhagic shock

We tested the ability of a nitric oxide (NO) scavenger to reduce tissue injury in a rodent model of hemorrhagic shock. Rats were hemorrhaged to a mean arterial blood pressure (MAP) of 40 mmHg and then resuscitated when either 30% of their shed blood had been returned (group 1) or after 100 min of continuous shock (group 2). Selected animals were treated with the NO scavenger NOX (30 mg. kg(-1). h(-1)) infused over 4 h. Hemorrhaged rats had a lower MAP after resuscitation compared with sham-shock control rats. NOX treatment significantly increased MAP after resuscitation from hemorrhage. Hemorrhagic shock also increased liver injury as reflected by elevated ornithine carbamoyltransferase (OCT) plasma levels, and NOX treatment significantly reduced OCT release. In addition, NOX was associated with significantly decreased hepatic neutrophil infiltration and improved 24-h survival (n = 8 of 9) compared with saline-treated shock animals (n = 3 of 9). These data suggest that excess NO mediates shock-induced tissue injury and that suppression of NO availability with NO scavengers may reduce the pathophysiological sequelae of severe hemorrhage.

[Serologic study of human herpesviruses 6 and 7 in lymphoma patients]

DNA sequences, antigens and elevated antibodies to HHV-6, and DNA sequences of HHV-7 in patients with Hodgkin's disease and non-Hodgkin's lymphoma have been detected. It is not known whether HHV-6 variants A and B, and HHV-7 contribute to the malignization by different ways, there is any interaction between these viruses, and their primary or recurrent infections occur during the disease progression. Total and high avidity IgG, IgM to HHV-6A, HHV-6B and HHV-7 were quantitated simultaneously in the sera of 12 patients with lymphomas and 12 control persons by indirect immunofluorescent assay and ELISA. It was established that, primary infection by HHV-6B in Hodgkin's disease, its primary or recurrent infections in non-Hodgkin's lymphoma; primary or recurrent infection by HHV-6A in Hodgkin's disease, its recurrent infection in non-Hodgkin's lymphoma; recurrent infection by HHV-7 in Hodgkin's disease may contribute to the deterioration of clinical conditions. Probably, HHV-7 exerts its effects through activating HHV-6B. The simultaneous effects of HHV-7 and HHV-6A, and that of HHV-6B and HHV-6A seem to be independent. Our results supports the recent opinion that, the effect of these herpesviruses on the tumorous cells is exerted indirectly by altered mediators of the immune system.

Neutrophil accumulation and damage to the gastric mucosa in resuscitated hemorrhagic shock is independent of inducible nitric oxide synthase

Polymorphonuclear leukocytes (PMN) and inducible nitric oxide synthase (iNOS) appear to play important roles in the liver and in lung injury induced by hemorrhagic shock. Their precise roles in hemorrhagic shock-induced acute gastric mucosal lesions (AGML), however, are still poorly understood. In this study, we investigated the effect of neutropenia on hemorrhagic shock-induced AGML. We also examined the roles of iNOS in PMN infiltration into the mucosa and AGML during hemorrhagic shock by using L-N6-(1-iminoethyl)-lysine, a potent inhibitor of iNOS, and by reverse transcriptase polymerase chain reaction. Remarkable gastric mucosal damage occurs after hemorrhagic shock. PMN depletion caused by Vinblastine pretreatment significantly attenuates this AGML. Although low-dose L-N6-(1-iminoethyl)-lysine (50 microg/kg, iNOS inhibition) has no effect on AGML, high-dose L-N6-(1-iminoethyl)-lysine (250 microg/kg, iNOS + endothelial NOS inhibition) significantly exacerbates AGML without increasing PMN infiltration into the mucosa. The mRNA expression of iNOS in the stomach during hemorrhagic shock cannot be detected by reverse transcriptase polymerase chain reaction. We conclude that PMN play a pivotal role in hemorrhagic shock-induced AGML, iNOS does not regulate PMN infiltration into the mucosa, and endothelial NOS provides important protection against AGML during hemorrhagic shock.

[Presence of antibodies to human herpesvirus type 6 and 7 in Hungarian children]

Prevalence of antibodies to variants HHV-6A and B as well as HHV-7, the time of primary infections are not know in Hungarian children. Therefore, antibodies to these viruses were studied in 21 healthy children aged between 6 and 18 months. Lymphoid cultures were infected with standard virus strains for indirect immunofluorescence. IgM, IgG and high avidity IgG after 8M urea treatment were quantified in serial dilutions of sera. It was established that, three of 13 boys had low level (1:20) IgG or IgM antibodies to HHV-6A, but all girls were negative. With exception of one girl and one boy, all had antibodies to HHV-6B in different titres (1:20 to 1:640 by immunofluorescence), in 9 cases only IgM, in further 4 cases only low avidity IgG were detected. Children studied gradually acquired symptom-free HHV-6B infection between age of 8 and 18 months. Antibodies to HHV-7 were found in 3 boys and one girl before their age of 12 months, but the majority were infected after that age. Approximately three quarters of children acquired either HHV-6B or HHV-7 before age of 18 months. More than half of the children were infected with HHV-6B prior to HHV-7. Antibody level to HHV-6B was slightly higher in boys, while that to HHV-7 was higher in girls. In Hungary, childhood infection with HHV-6A seems to be a very rare event. Epidemiology of HHV-6B primary infection is similar to that of industrial countries, while that of HHV-7 resembles data of developing world: onset of antibodies occurs 1 or 2 years earlier than in the industrial nations.

The Epstein-Barr virus (EBV) major envelope glycoprotein gp350/220-specific antibody reactivities in the sera of patients with different EBV-associated diseases

gp350 of Epstein-Barr virus (EBV) induces a strong immune response in EBV-infected individuals, but relatively little is known about the clinical relevance of this response in patients with different EBV-associated malignancies and other diseases. Using our gp350-expressing cell clones, we studied gp350-specific humoral immune responses in the sera of individuals with nasopharyngeal carcinoma (NPC), chronic symptomatic EBV infection (CEI), Hodgkin's disease (HD), acute infectious mononucleosis (IM) and healthy EBV-seropositive individuals (HI). The titres of antibody-dependent cellular cytotoxicity (ADCC) antibodies were highest in HI followed by CEI, HD and NPC. EBV-neutralizing (NA) and gp350-specific IgG antibody profiles in these conditions were: CEI > HI > NPC > HD, whereas IgA titres were the highest in NPC sera followed by CEI and HD. The sera from IM patients were found to be negative for gp350-specific ADCC and IgA activities. Sera from HI were also negative for gp350-specific IgA. A significant positive correlation was found between serum gp350 IgA and viral capsid antigen IgA and a significant negative one between IgM and ADCC titres. High IgA titres were also found in CEI and EBV-genome positive HD in addition to NPC. Importantly, gp350-specific IgA titres were of prognostic value in NPC patients. Our data provide new insights about the clinical relevance of gp350-specific immune responses in these diseases.

Binding of the endogenously expressed Epstein-Barr virus (EBV) envelope glycoprotein gp350 with the viral receptor masks the major EBV-neutralizing epitope and affects gp350-specific ADCC

The major neutralizing epitope (MNE) for the Epstein-Barr virus (EBV) is present on its envelope glycoprotein gp350/220 (hereafter referred to as gp350) in close proximity to the virus-receptor (CR2) binding site and is recognized by the neutralizing murine monoclonal antibody (mAb) 72A1. We studied the reactivities of 72A1 and another anti-gp350 mAb 2L10 (which does not neutralize EBV) with gp350 expressed on three different lymphoid cell lines (Raji, CEM.NKr and BJA-B). Our results indicate that gp350 expressed on the surface of CR2-positive cells interacts with the viral receptor and that this interaction masks the major EBV-neutralizing epitope. The interaction was reversible and the masked epitope was revealed on incubation with an excess of anti-CR2 mAb OKB7. Gp350-expressing CEM-NKr cells with intact MNE exhibited significantly higher (P < or = 0.05) lysis in gp350-specific antibody-dependent cellular cytotoxic assays compared with its Raji counterpart. The present results may have important implications for the use of soluble viral receptors as therapeutic agents in acute and chronic EBV and other viral infections (e.g., HIV-1).

Enhancement of natural killer cell cytotoxicity by the human herpesvirus-7 via IL-15 induction

NK cells, a key component of the innate immune system, are known to play an important role against viral infections. Previously, we reported that the human herpesvirus-6 (HHV-6) induces IL-15 in human PBMC and increases their NK activity. We describe in this work that another human herpesvirus, HHV-7, which shares genomic homology with HHV-6, also causes up-regulation of NK cell cytotoxicity via IL-15 induction. The NK cell activity of the PBMC from different donors displayed a variable range of enhancement after treatment with HHV-7. This enhancement occurred within a few hours of exposure to the virus and was blocked by Abs to IL-15, but not to other cytotoxicity-enhancing cytokines (i.e., to IFN-gamma, IL-2, TNF-alpha, or IL-12). Our results also show that this HHV-7-induced IL-15-mediated activation of NK cells occurs via IL-2R, since HHV-7-enhanced NK cytotoxic activity could be blocked completely by anti-IL-2R beta-chain mAb (anti-CD122). The up-regulation of NK cell cytotoxicity did not require infectious virus, as the use of UV-irradiated HHV-7 produced similar results. This effect was virus specific because it was abrogated by neutralizing the virus with human sera containing Abs to HHV-7. We also found increased amount of IL-15 transcripts in HHV-7-treated PBMC as compared with the untreated PBMC. Taken together, these results would suggest that host responds to HHV-7 infection by up-regulating IL-15 production, which then results in an enhancement of NK cell activity; this, in turn, may play a major role in the control of the viral infection.

Enhancement of natural killer cell cytotoxicity by the human herpesvirus-7 via IL-15 induction

NK cells, a key component of the innate immune system, are known to play an important role against viral infections. Previously, we reported that the human herpesvirus-6 (HHV-6) induces IL-15 in human PBMC and increases their NK activity. We describe in this work that another human herpesvirus, HHV-7, which shares genomic homology with HHV-6, also causes up-regulation of NK cell cytotoxicity via IL-15 induction. The NK cell activity of the PBMC from different donors displayed a variable range of enhancement after treatment with HHV-7. This enhancement occurred within a few hours of exposure to the virus and was blocked by Abs to IL-15, but not to other cytotoxicity-enhancing cytokines (i.e., to IFN-gamma, IL-2, TNF-alpha, or IL-12). Our results also show that this HHV-7-induced IL-15-mediated activation of NK cells occurs via IL-2R, since HHV-7-enhanced NK cytotoxic activity could be blocked completely by anti-IL-2R beta-chain mAb (anti-CD122). The up-regulation of NK cell cytotoxicity did not require infectious virus, as the use of UV-irradiated HHV-7 produced similar results. This effect was virus specific because it was abrogated by neutralizing the virus with human sera containing Abs to HHV-7. We also found increased amount of IL-15 transcripts in HHV-7-treated PBMC as compared with the untreated PBMC. Taken together, these results would suggest that host responds to HHV-7 infection by up-regulating IL-15 production, which then results in an enhancement of NK cell activity; this, in turn, may play a major role in the control of the viral infection.

Enhancement of natural killer and antibody-dependent cytolytic activities of the peripheral blood mononuclear cells of HIV-infected patients by recombinant IL-15

Natural killer (NK) cells are an important subset of lymphocytes capable of killing virus-infected target cells without prior sensitization. HIV-infected individuals show impairment of their NK cell activity. Although the mechanism responsible for this defect remains unclear, NK cytotoxicity of lymphocytes from these individuals can be partially restored by interleukin (IL)-2. IL-15 is a recently discovered cytokine that shares many biologic activities with IL-2--for example, enhancement of NK activity. In this study, we investigated the effect of recombinant IL-15 (rIL-15) on the NK and antibody-dependent cellular cytotoxicity (ADCC) effector activities of peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals using K562 cell line and HIV gp120-expressing cells. The effect of anti-IL-15 antibodies on NK activity was also examined using PBMCs of HIV-seronegative individuals. Our results show that NK and ADCC activities of PBMCs in HIV-seropositive patients were significantly lower than those of seronegative donors (p < or = 0.05). However, these two activities were significantly enhanced when rIL-15 was added to the assay wells (p < or = 0.05). Moreover, addition of saturating concentrations of neutralizing monoclonal antibodies (mAb) specific for IL-2, IL-12, or interferon (IFN)-gamma in the assays failed to inhibit IL-15-mediated enhancement of NK cell functions. Only the antibody against IL-15 abrogated the upregulation of NK and ADCC activities mediated by IL-15, suggesting that this cytokine enhances NK cell functions through a mechanism that is independent of the induction of other cytokines. IL-15 did not exert any modulatory effect on the expression of CD16 or CD56 molecules. Our results show that IL-15 can increase the NK and ADCC activities of the PBMCs of HIV-infected individuals in vitro. In view of its higher therapeutic index as determined using murine models, IL-15 may represent a better immunotherapeutic agent than IL-2 to restore these functions in HIV-seropositive patients.

Binding of the Epstein-Barr virus to human platelets causes the release of transforming growth factor-beta

Human platelets bear on their surface complement receptor type II (CR2), which is also the receptor for the EBV. Although the cross-linking of these receptors causes activation and aggregation of platelets, no immunologic consequence of the potential binding of EBV to these receptors on human platelets has ever been described. We report here that binding of EBV to human platelets causes the release of TGF-beta from the latter. Both infectious and UV-inactivated noninfectious viral particles can mediate this release. Anti-CR2 mAb OKB7, which blocks the binding of EBV to CR2, also blocks the EBV-mediated release of TGF-beta. Furthermore, platelets recovered from the initial incubation no longer release TGF-beta upon subsequent incubation with EBV. Since TGF-beta is a potent immunosuppressive agent, its release from platelets upon binding of EBV may play a role in the pathogenesis of EBV-associated diseases.

Binding of the Epstein-Barr virus to human platelets causes the release of transforming growth factor-beta

Human platelets bear on their surface complement receptor type II (CR2), which is also the receptor for the EBV. Although the cross-linking of these receptors causes activation and aggregation of platelets, no immunologic consequence of the potential binding of EBV to these receptors on human platelets has ever been described. We report here that binding of EBV to human platelets causes the release of TGF-beta from the latter. Both infectious and UV-inactivated noninfectious viral particles can mediate this release. Anti-CR2 mAb OKB7, which blocks the binding of EBV to CR2, also blocks the EBV-mediated release of TGF-beta. Furthermore, platelets recovered from the initial incubation no longer release TGF-beta upon subsequent incubation with EBV. Since TGF-beta is a potent immunosuppressive agent, its release from platelets upon binding of EBV may play a role in the pathogenesis of EBV-associated diseases.

Antibody and antibody-dependent cellular cytotoxicity responses against the BamHI A rightward open-reading frame-1 protein of Epstein-Barr virus (EBV) in EBV-associated disorders

Antibody-dependent cellular cytotoxicity (ADCC) is an important antiviral effector mechanism. ADCC to the protein encoded by the Epstein-Barr virus (EBV) BamHI A rightward open-reading frame-1 (BARF1) was studied by transducing Raji-tk- cells with the BARF1 gene using a retroviral expression vector. The transduced Raji cells expressed BARF1 on the cell surface, as determined by flow cytometry. Sera from chronic and acute infectious mononucleosis and nasopharyngeal carcinoma patients were found to contain antibodies that react with the BARF1 protein. When BARF1-expressing Raji cells were used as targets for ADCC, sera from several nasopharyngeal carcinoma patients demonstrated significant ADCC reactivity, whereas sera from healthy EBV-seronegative and -seropositive persons lacked such reactivity. BARF1-specific ADCC activity could be competitively inhibited with recombinant BARF1 protein. The level of anti-BARF1 antibody activity in sera of patients with EBV-associated diseases suggests that the BARF1 protein may serve as a target on EBV-infected cells for ADCC.

Effect of adoptive transfer of CD4, CD8 and B cells on recovery from MHV3-induced immunodeficiencies

A chronic viral infection can occur when the host fails to mount an effective immune response to clear the virus. Mouse hepatitis virus type 3 (MHV3) appears to be an excellent model for the study of the relationship between viral-induced immunodeficiency and chronic disease development. (C57BL/6 x A/J)F1 mice surviving acute hepatitis develop a chronic disease characterized by T- and B-cell immunodeficiencies, viral persistence in various organs including the brain, spleen and thymus, and death within 3 months postinfection (p.i.). We have reported that T- or B-cell deficiencies, observed in MHV3 chronically infected (C57BL/6 x A/J)F1 mice, can be partially or totally thwarted by adoptive transfer of CD4+, CD8+ and/or B cells, at 15 days p.i. in mice surviving the acute phase of the disease. Adoptive transfer of syngeneic CD4+ and/or CD8+ allowed a partial restoration of the T-cell deficiencies, as characterized by thymic atrophy, decrease in splenic T cells, and in all thymocyte subpopulations. B-cell immunodeficiency, as defined by a decrease in splenic B cells, as well as in the bone marrow pre-B- and B-cell compartments, and the occurrence of abnormally larger forms of bone marrow pre-B and B cells, were partially thwarted by B-cell treatment only. Splenic B cells and the bone marrow B-cell compartment, respectively, returned partially or totally to normal values, whereas the pre-B-cell compartment remained depleted in infected mice treated with B cells. Levels of all immunoglobulin classes returned to normal values in MHV3 chronically infected mice when treated with CD4+ in combination with CD8+ cells. All T- and/or B-cell treatments, however, were sufficient to thwart the process of the chronic disease, and favoured the survival of mice for up to 6 months p.i.

Human herpesvirus-6 enhances natural killer cell cytotoxicity via IL-15

The marked tropism of human herpesvirus-6 (HHV-6) for natural killer (NK) cells and T lymphocytes has led us to investigate the effect of HHV-6 on cellular cytotoxicity. We describe here how HHV-6 infection of peripheral blood mononuclear cells (PBMC) leads to upregulation of their NK cell cytotoxicity. The induction of NK cell activity by HHV-6 was abrogated by monoclonal antibodies (mAbs) to IL-15 but not by mAbs to other cytokines (IFN-alpha, IFN-gamma, TNF-alpha, TNF-beta, IL-2, IL-12) suggesting that IL-15 secreted in response to viral infection was responsible for the observed effect. Furthermore, NK activation by HHV-6 was blocked with mAb to CD122, as well as by human anti-HHV-6 neutralizing antibodies. Using RT-PCR, we were able to detect IL-15 mRNA upregulation in purified monocyte and NK cell preparations. IL-15 protein synthesis was increased in response to HHV-6. Finally, addition of IL-15 to PBMC cultures was found to severely curtail HHV-6 expression. Taken together, our data suggest that enhanced NK activity in response to viral infection represent a natural anti-viral defense mechanism aimed at rapidly eliminating virus-infected cells.

Cyclic AMP-responsive element-dependent activation of Epstein-Barr virus zebra promoter by human herpesvirus 6

We have recently shown that infection of Epstein-Barr virus (EBV) genome-positive B cells by human herpesvirus 6 (HHV-6) results in the expression of the immediate-early EBV Zebra gene, followed by virus replication (L. Flamand, I. Stefanescu, D. V. Ablashi, and J. Menezes, J. Virol. 67:6768-6777, 1993). Here we show that HHV-6 upregulates Zebra gene transcription through a cyclic AMP-responsive element (CRE) located within the Zebra promoter (Zp). Using human B- or T-cell lines transfected with ZpCat reporter gene constructs, we demonstrate that a region designated the ZII domain of Zp is the target of HHV-6 transactivation. Mutation of the consensus AP-1/CRE site within ZII abolished the inducibility of Zp by HHV-6, whereas positioning of the ZII domain upstream of the beta-globin minimal promoter conferred responsiveness following HHV-6 infection. Binding of these factors to ZII was prevented by oligonucleotides containing CRE but not by AP-1 consensus sequences. Antibodies against CRE-binding (CREB) protein but not against c-Fos or c-Jun were able to supershift the DNA-protein complex, identifying the nature of the transcription factor which binds to ZII as a member of the CREB family of proteins. Finally, transfection of CREB protein and protein kinase A expression vectors were found to activate Zp in Jurkat cells, suggesting that phosphorylated form of CREB protein can play a determining role in the EBV reactivation process.

Defective killing activity against gp120/41-expressing human erythroleukaemic K562 cell line by monocytes and natural killer cells from HIV-infected individuals

OBJECTIVE

To determine the role of natural cellular cytotoxicity of peripheral blood mononuclear cells (PBMC) in killing of HIV-1 envelope protein-expressing, natural killer (NK)-sensitive human target cells, and to investigate this effector function in HIV-infected individuals.

DESIGN AND METHODS

An HIV-1 env gene-containing expression vector was transfected into NK-sensitive K562 cells, and cell clones expressing gp120/41 were selected and used as targets in natural cytotoxicity assays using PBMC from both HIV-seropositive and seronegative individuals. A 16h 51Cr-release assay was used to determine the susceptibility of the gp120/41-expressing K562 as well as control vector-transfected cells. To identify the cell types involved in the killing of the transfected cells, PBMC depleted for a specific cell type as well as enriched or purified cell types were used as effector cells.

RESULTS

Endogenous expression of gp120/41 by target cells increased their susceptibility to lysis by PBMC of HIV-seronegative individuals. The two cell types responsible for this enhanced killing, NK cells and monocytes, were found severely compromised in HIV-seropositive individuals in their ability to kill both env gene-transfected and control cells; killing by monocytes occurred via CD4.

CONCLUSIONS

The present results illustrate for the first time that the transfected gp120/41 serves as target for both NK and monocyte-mediated killing and that cytocidal activity of these two effector cell types is defective in HIV-infected subjects. Strengthening this innate cytotoxic activity in these individuals may represent a valuable approach in controlling HIV infection.

Antibody-dependent cellular cytotoxicity in HIV infections

ADCC is an important immune effector mechanism against tumor and virus-infected cells that can be destroyed by the combined action of specific antibodies of IgG isotype against cell surface-associated antigens and effector cells, predominantly of the NK phenotype. ADCC has been shown to function in vivo in several systems. With regard to HIV, it can be readily demonstrated in vitro against the viral envelope proteins with serum and/or effector cells obtained from HIV-infected subjects. Several studies have demonstrated that the titers of the envy-specific ADCC-mediating antibodies decrease in the sera of HIV-infected individuals as the infection progresses toward AIDS. The cells that mediate ADCC also become functionally compromised in these individuals in early stages of the infection, thus depriving the host of the potential benefits of this process. Restoration of this process in the infected individuals by the administration of functionally competent effector cells (in vitro expanded and lymphokine-activated killer cells) and ADCC-mediating antibodies (hyperimmune serum or appropriate monoclonal antibodies), alone or in combination, may help slow the disease progress. Because of the multicomponent nature of the process, ADCC-mediating antibodies may prove a better correlate of protection and prognosis than the virus-specific neutralizing antibodies and cytotoxic T cells in assessing anti-HIV immunization and immunotherapy.

Positive correlation between the natural killer and gp 120/41-specific antibody-dependent cellular cytotoxic effector functions in HIV-infected individuals

Using our recently developed target system model of env gene-transfected cells for gp120/41-specific antibody-dependent cellular cytotoxicity (ADCC) assays, we evaluated the ADCC effector function of the peripheral blood mononuclear cells (PBMC) in 39 human immunodeficiency virus type 1 (HIV-1)-infected individuals. The natural killer (NK) activity of the PBMC from these individuals against K562 was also determined. A significant positive correlation (p < or = 0.05, r = 0.37) was found between these two activities. On the basis of our data, we built a regression equation for the two activities whereby the ADCC effector function of PBMC of an HIV-infected individual can be predicted from their NK activity. We also found that the endpoint titer of a given serum for ADCC-mediating antibodies in the ADCC assay varied depending on the NK activity of the effector cells used: The effectors with high NK activity tended to give higher titers as compared with the effectors with low NK activity. To our knowledge, this is the first formal documentation of the existence of a positive correlation between the ADCC and NK activities of the PBMC. It also shows that the ADCC titer of serum in ADCC assay may vary depending on the NK activity of the effector cells used. This observation underscores an important variable of ADCC assays. Using our statistical model, one can predict the ADCC effector function of the PBMC from HIV-infected individuals from their NK activity and thus help clarify the role of this important immune response in HIV infection and AIDS prognosis.

Immunosuppressive effect of human herpesvirus 6 on T-cell functions: suppression of interleukin-2 synthesis and cell proliferation

Human herpesvirus-6 (HHV-6), the etiologic agent of roseola, is ubiquitous, establishes latency in the host, and can infect a variety of immunocompetent cells, with CD4+ T lymphocytes being the targets in which it replicates most efficiently. The present study was undertaken to learn more about specific immunobiologic effects of HHV-6 infection on T-lymphocyte functions. Our data demonstrate that infection of peripheral blood mononuclear cells (PBMC) by HHV-6 results in suppression of T-lymphocyte functions, as evidenced by reduced interleukin-2 (IL-2) synthesis and cellular proliferation. In fact, HHV-6-infected PBMC secreted 50% less IL-2 than mock-infected cells after mitogenic stimulation with OKT3 antibody or phytohemmaglutinin (PHA). The inhibition of IL-2 by HHV-6 was also observed in enriched T-cell cultures, suggesting a direct effect of this virus on this cell type. Messenger RNA (mRNA) analysis by reverse-transcriptase polymerase chain reaction (PCR) indicated that HHV-6 diminishes IL-2 mRNA levels in mitogen-stimulated peripheral blood T cells. These results were also confirmed by Northern blot using the leukemic T-cell line Jurkat. This inhibitory effect of HHV-6 did not require infectious virus, as the use of UV-irradiated HHV-6 produced similar results. Moreover, HHV-6-infected PBMC showed up to an 85% reduction in their mitogen-driven proliferative response, as compared with sham-infected cells. Proliferation of both CD4+ and CD8+ T cells was affected by HHV-6. Taken together, our data show that infection of T cells by HHV-6 results in immune suppression characterized by a downregulation of IL-2 mRNA and protein synthesis accompanied by diminished cellular proliferation.

Interleukin-6 and Epstein-Barr virus induction by cyclosporine A: potential role in lymphoproliferative disease

Posttransplant patients undergoing prolonged cyclosporine A (CsA) immunosuppressive therapy have been reported to have increased incidence of Epstein-Barr virus (EBV)-associated lymphoproliferative disorders. We undertook experiments to analyze the possible actions of CsA during EBV-infection of human peripheral blood mononuclear cells (PBMC). EBV-infected B cells cultured with CsA demonstrated increased EBV B-cell outgrowth as compared with those cultured without CsA. PBMC, after infection with EBV and CsA treatment, demonstrated increased interleukin-6 (IL-6) activity in the culture supernatant. The induction of IL-6 appears to differ within the various lymphocyte populations. In monocytes, IL-6 expression appears preferentially induced by EBV and is initiated by the binding of the two major virion glycoproteins, gp350 and gp220. Expression of IL-6 in T cells appears to be due mainly to CsA. B cells also express IL-6 after EBV exposure, but not after CsA treatment. EBV-immortalized B-cell lines cultured with CsA exhibited both an increased number of cells expressing viral lytic-cycle antigens and increased amounts of lytic-cycle proteins. IL-6, which is induced by CsA in PBMC, was also capable of inducing the lytic viral cycle in several EBV-immortalized cells. CsA, in promoting both increased numbers of lytic EBV B cells and an EBV paracrine factor, IL-6, within the microenvironment of EBV B cell:T cell and EBV B cell:monocyte interactions, may result in increased EBV B-cell immortalization and ultimately lead to the promotion of B-cell lymphomas in immunosuppressed patients.

Epstein-Barr virus gp350-specific antibody titers and antibody-dependent cellular cytotoxic effector function in different groups of patients: a study using cloned gp350-expressing transfected human T cell targets

An NK cell activity-resistant human lymphoid T cell line (CEM-NKr) expressing the transfected Epstein-Barr virus (EBV) gp350 gene was used in membrane immunofluorescence (MIF) and antibody-dependent cellular cytotoxicity (ADCC) assays to analyze the gp350-specific humoral and ADCC responses in groups of EBV-seropositive persons. Results show that there is no correlation between gp350-specific ADCC-mediating antibody titers and MIF or EBV neutralizing antibody titers. For example, sera from patients in the acute phase of infectious mononucleosis, while positive by MIF assay or EBV neutralization test, were not reactive in the ADCC assay. Results also show that nasopharyngeal carcinoma (NPC) patients on MIF present high IgG titers against gp350 compared with healthy persons. Anti-gp350 IgA antibodies were detected in all groups tested; however, titers were highest in the NPC group.

Surface expression of the HIV-1 envelope proteins in env gene-transfected CD4-positive human T cell clones: characterization and killing by an antibody-dependent cellular cytotoxic mechanism

The env gene of the human immunodeficiency virus-type 1 (HIV-1) was transfected in CEM-nkr, a human lymphoid cell line of T lineage that is resistant to the activity of natural killer cells, and for the first time, transfected T cell clones were established that stably express gp160 intracellularly and gp120 on the surface as demonstrated by radioimmunoprecipitation as well as by indirect membrane immunofluorescence. The regulatory protein vpu was not detected by radioimmunoprecipitation in these clones. The surface expression of gp120 without vpu in these clones provides direct evidence that gp160 is processed and cleaved (without vpu) in CD4+ cells. The CD4 antigens of these cells coprecipitated gp160; interestingly, no reduction of the surface CD4 expression (detectable by flow cytometric analysis of membrane immunofluorescence with OKT4) in the transfected cells was observed. However, decreased reactivity of the transfected clones with OKT4A was observed. The gp120-expressing cells did not form syncytia on coculture with other CD4+ human cell lines. These observations suggest the binding of gp120 to the surface CD4 antigen of the transfected cells. The transfected cells retained their resistance to the activity of the natural killer cells but showed a significant (p < 0.05) lysis when they were preincubated with AIDS patients' serum containing anti-gp120/41 antibodies. Thus, the expressed gp120/41 in these cells made them susceptible to killing by an antibody-dependent cellular cytotoxicity (ADCC) mechanism. To our knowledge, these are the first reported CD4+ T cell lines that stably express HIV envelope proteins. These cell lines would be useful as targets in exploring gp120/41-specific immune responses, especially in conducting gp120/41-specific ADCC studies in HIV-infected or gp120/41 (gp160)-vaccinated individuals.

Evidence for a defect of antibody-dependent cellular cytotoxic (ADCC) effector function and anti-HIV gp120/41-specific ADCC-mediating antibody titres in HIV-infected individuals

Antibody-dependent cellular cytotoxicity (ADCC) is an important antiviral effector mechanism. However, its role, as well as the functional integrity of the ADCC-effector cells in HIV infections, is not well understood. For studying gp120/41-specific ADCC, we recently developed a virus-free target cell system, using a natural killer (NK) cell activity-resistant human lymphoid cell line of B lineage, which was transfected with the env gene of the human immunodeficiency virus type 1 (HIV-1); gp120/41-expressing cell clones were thus selected. In this study, these gp120/41-expressing cloned cells were used as targets in a gp120/41-specific ADCC assay for (a) examining the functional integrity of ADCC-effector cells from HIV-seropositive individuals, and (b) titrating the sera of these individuals for gp120/41-specific, ADCC-mediating antibodies. Our data indicate for the first time that the percentage of sera positive for ADCC-mediating antibodies to gp120/41 is higher in individuals with CD4 counts < or = 400 and > or = 200/mm3. The individuals with CD4 counts < 200/mm3 were found to have the lowest titers of these antibodies in their sera. The ADCC-effector function of the peripheral blood mononuclear cells (PBMC) of HIV-infected individuals was significantly (p < 0.05) reduced as compared to the PBMC from healthy, HIV-seronegative individuals. Further, human recombinant IL2 and interferon-gamma were found to exert a significant (p < 0.05) enhancing effect on ADCC mediated by PBMC from these HIV-infected individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Genomic organization and mapping of transcription and translation products of the NADL-2 strain of porcine parvovirus

The NADL-2 strain of PPV was cloned into pUC19 and independent infectious clones were sequenced. This permitted a correction of published sequences and to predict a cruciform structure as an alternative to the 5'-hairpin of the "-" strand. This 5'-end structural covariance is shared with other parvoviruses of the same group and two alternative sequences ("flip" and "flop") were present in the region of the cruciform. Transcript and translation product mapping allowed the prediction of the location of the different expression signals. The 5'-startpoints of the transcripts were located at nucleotides 225 and 2035, respectively, and the polyadenylation site at nucleotides 4829-4833. This indicated that the TATA boxes at 196-TATA and 2004-AATA and the 4813-AATAAA polyadenylation sequence would be functional. Alternative splicing of capsid gene (VP) transcripts (either 2280-AG/GT or 2313-AG/GT spliced with 2386-AG/GA), to maintain or remove the first AUG (at 2287) in the ORF, yielded two 2.9-kb mRNAs containing a nested set of protein-coding sequences (VP-1 and VP-2 with predicted molecular mass 80.9 and 64.3 kDa, respectively). Three nonstructural (NS) protein gene transcripts were identified. The 4.7-kb transcript was not spliced in the NS gene and was predicted to code for a 75.5-kDa protein (NS-1; published value of phosphorylated form 84 kDa). The splicing sites of two different 3.3-kb NS transcripts were analyzed. These transcripts were predicted to code for the NS-2 protein (18.1 kDa). Of the two NS-2 transcripts, one had also the VP-intron removed downstream of the NS-2 coding sequences. A 2.9-kb transcript would code for an NS-3 protein (12.4 kDa) although such a protein has not been described before. A flow chart of the information from the viral DNA to the viral proteins is presented and several differences, both for the NS and the VP genes, with closely related parvoviruses are noted.

Activation of the Epstein-Barr virus replicative cycle by human herpesvirus 6

One common attribute of herpesviruses is the ability to establish latent, life-long infections. The role of virus-virus interaction in viral reactivation between or among herpesviruses has not been studied. Preliminary experiments in our laboratory had indicated that infection of Epstein-Barr virus (EBV) genome-positive human lymphoid cell lines with human herpesvirus 6 (HHV-6) results in EBV reactivation in these cells. To further our knowledge of this complex phenomenon, we investigated the effect of HHV-6 infection on expression of the viral lytic cycle proteins of EBV. Our results indicate that HHV-6 upregulates, by up to 10-fold, expression of the immediate-early Zebra antigen and the diffuse and restricted (85 kDa) early antigens (EA-D and EA-R, respectively) in both EBV producer and nonproducer cell lines (i.e., P3HR1, Akata, and Raji). Maximal EA-D induction was observed at 72 h post-HHV-6 infection. Furthermore, expression of late EBV gene products, namely, the viral capsid antigen (125 kDa) and viral membrane glycoprotein gp350, was also increased in EBV producer cells (P3HR1 and Akata) following infection by HHV-6. By using dual-color membrane immunofluorescence, it was found that most of the cells expressing viral membrane glycoprotein gp350 were also positive for HHV-6 antigens, suggesting a direct effect of HHV-6 replication on induction of the EBV replicative cycle. No expression of late EBV antigens was observed in Raji cells following infection by HHV-6, implying a lack of functional complementation between the deleted form of EBV found in Raji cells and the superinfecting HHV-6. The susceptibility of the cell lines to infection by HHV-6 correlated with increased expression of various EBV proteins in that B95-8 cells, which are not susceptible to HHV-6 infection, did not show an increase in expression of EBV antigens following treatment with HHV-6. Moreover, UV light-irradiated or heat-inactivated HHV-6 had no upregulating effect on the Zebra antigen or EA-D in Raji cells, indicating that infectious virus is required for the observed effects of HHV-6 on these EBV products. These results show that HHV-6, another lymphotropic human herpesvirus, can activate EBV replication and may thus contribute to the pathogenesis of EBV-associated diseases.

Interleukin-2 production in pediatric inflammatory bowel disease: evidence for dissimilar mononuclear cell function in Crohn's disease and ulcerative colitis

Crohn's disease (CD) and ulcerative colitis (UC) represent clinically distinct chronic inflammatory bowel diseases (IBD) of unknown etiology. Although the mucosal immune system is implicated in their pathogenesis, immunological differences between the two disorders are not well defined. The aim of this study was to compare in vitro mucosal T-lymphocyte function in CD and UC. Peripheral blood mononuclear cell interleukin-2 (IL-2) production was similar in pediatric IBD and control patients under unstimulated conditions, but was significantly increased in response to phytohemagglutinin (PHA) stimulation for the UC group. Lamina propria mononuclear cells (LPMNC) isolated from colonic resections in IBD patients had significantly lower spontaneous proliferation and IL-2 production in vitro than did LPMNC of control patients. In contrast, significantly greater IL-2 production was detected when the LPMNC of CD patients were cultured with PHA, in comparison with those of UC or control patients. When indomethacin, a prostaglandin synthetase inhibitor, was added to the cultures, significantly increased IL-2 secretion was observed for CD LPMNC, but not for UC cultures, under both stimulated and unstimulated conditions. These findings demonstrate abnormal LPMNC IL-2 production in IBD. Furthermore, our data suggest that inhibition of the prostaglandin synthetase pathway upregulates IL-2 production by LPMNC in CD. These results support the hypothesis that immunoregulatory mechanisms controlling IL-2 production differ between CD and UC.

The use of topical phenytoin as an adjunct to immobilization in the treatment of trophic leprosy ulcers

A total of 30 leprosy patients (controls n = 16; topical phenytoin n = 14) with trophic ulcers on the feet were investigated to ascertain the efficacy of topical phenytoin powder in the healing of ulcers. The ulcers in the two groups were matched for initial size. Healing patterns were assessed by determining changes in depth and planar (surface) dimensions at weekly intervals over a three week study period. Results indicate that while immobilization of the ulcer site is effective in promoting ulcer healing, additional use of topical phenytoin accelerates the healing process. There may however be non-responders to topical phenytoin.

Stable expression of the transfected HIV-1 env gene in a human B cell line: characterization of gp120-expressing clones and immunobiological studies

The env gene of human immunodeficiency virus type 1 (HIV-1) encodes gp 120/41 which plays an important role in the viral infection process and pathogenesis. The surface glycoprotein gp120 is a candidate molecule for the development of a subunit vaccine against HIV-1-induced acquired immunodeficiency syndrome (AIDS). However, thorough studies on the immunobiology of this molecule are hampered by the lack of a suitable model. With this background in mind, and in order to learn more on anti-gp120 cellular immunity, we attempted to develop gp120-expressing human cell clones. Thus by transfecting a human lymphoid cell line of B lineage (Raji), which is known to be resistant to the natural killer cell activity, with an expression vector encoding the envelope and vpu, we established three clones that stably express gp120/41 and vpu. The surface glycoprotein gp 120 is also expressed on the cell surface of these clones. The transfected cells from syncytia with CD4+ human cell lines as well as with peripheral blood mononuclear cells (PBMC) leading to the death of the fused cells. This observation represents additional evidence for the eventual depletion of CD4+ viral targets that fuse with adjacent HIV-infected, gp 120-expressing cells. The latent Epstein-Barr virus genome present in the transfected cells, was not induced to express the lytic cycle antigens. The densities of the surface expression of a number of molecules examined remained unchanged in the transfected cells except for the surface IgM, which increased significantly (P < 0.05) in two clones. One of the clones exhibited a significantly (P < 0.05) reduced proliferation rate as compared to the other clones. The transfected cells of all the three clones showed a significantly (P < 0.01) increased susceptibility to lysis by the PBMC from normal, healthy individuals in a 16-hr 51Cr-release assay. This is the first report of the MHC- and antibody-independent lysis of human cells transfected with the HIV-1 surface glycoprotein. The transfected cells also served as targets in a gp120-specific antibody-dependent cellular cytotoxicity assay. We anticipate that the present model will prove very useful for studying the gp120-specific immune responses in HIV-infected individuals.

Modulatory effects of Epstein-Barr, herpes simplex, and human herpes-6 viral infections and coinfections on cytokine synthesis. A comparative study

Herpesviruses such as EBV, HSV, and human herpes virus-6 (HHV-6) have a marked tropism for cells of the immune system and therefore infection by these viruses may result in alterations of immune functions, leading at times to a state of immunosuppression. We report the results of a comparative study in which we found that EBV, HSV-1, and HHV-6 act differentially on the immune system with regard to their effect on the synthesis of IL-1 beta, IL-6, and TNF-alpha, i.e., three immunoregulatory cytokines mainly secreted by activated monocytes/macrophages. Using the polymerase chain reaction technique, analyses of the mRNA levels for each of the three monokines after viral infection indicated that the effect exerted by each of these herpesviruses on cytokine synthesis by human PBMC was detectable at the transcriptional level. Different amounts of IL-1 beta protein were detected in infected PBMC cultures, HHV-6 being the strongest IL-1 beta up-regulatory among these three herpesviruses. Spontaneous releases of IL-6 and TNF-alpha were found reduced after infection by HHV-6 and EBV, respectively. In comparison to EBV and HHV-6, HSV-1 proved to be a weak monokine enhancer. Results of coinfection studies indicated that virus-induced suppressive effects on cytokine synthesis are dominant. In fact, EBV inhibited TNF-alpha synthesis even in the presence of HHV-6, a strong up-regulator of TNF-alpha synthesis. Similarly, EBV was unable to stimulate IL-6 production in the presence of HHV-6. Viral structural component(s) appeared to be responsible for the up-regulation of IL-6 by both EBV and HSV-1, and of TNF-alpha by HSV-1. Taken together, our observations illustrate that herpesviruses can selectively regulate cytokine synthesis thereby disturbing immune homeostasis; this effect may favor pathogenic events, including the reactivation and/or spread of other infectious agents within the host.

Modulatory effects of Epstein-Barr, herpes simplex, and human herpes-6 viral infections and coinfections on cytokine synthesis. A comparative study

Herpesviruses such as EBV, HSV, and human herpes virus-6 (HHV-6) have a marked tropism for cells of the immune system and therefore infection by these viruses may result in alterations of immune functions, leading at times to a state of immunosuppression. We report the results of a comparative study in which we found that EBV, HSV-1, and HHV-6 act differentially on the immune system with regard to their effect on the synthesis of IL-1 beta, IL-6, and TNF-alpha, i.e., three immunoregulatory cytokines mainly secreted by activated monocytes/macrophages. Using the polymerase chain reaction technique, analyses of the mRNA levels for each of the three monokines after viral infection indicated that the effect exerted by each of these herpesviruses on cytokine synthesis by human PBMC was detectable at the transcriptional level. Different amounts of IL-1 beta protein were detected in infected PBMC cultures, HHV-6 being the strongest IL-1 beta up-regulatory among these three herpesviruses. Spontaneous releases of IL-6 and TNF-alpha were found reduced after infection by HHV-6 and EBV, respectively. In comparison to EBV and HHV-6, HSV-1 proved to be a weak monokine enhancer. Results of coinfection studies indicated that virus-induced suppressive effects on cytokine synthesis are dominant. In fact, EBV inhibited TNF-alpha synthesis even in the presence of HHV-6, a strong up-regulator of TNF-alpha synthesis. Similarly, EBV was unable to stimulate IL-6 production in the presence of HHV-6. Viral structural component(s) appeared to be responsible for the up-regulation of IL-6 by both EBV and HSV-1, and of TNF-alpha by HSV-1. Taken together, our observations illustrate that herpesviruses can selectively regulate cytokine synthesis thereby disturbing immune homeostasis; this effect may favor pathogenic events, including the reactivation and/or spread of other infectious agents within the host.

Infection of peripheral blood mononuclear cells by herpes simplex and Epstein-Barr viruses. Differential induction of interleukin 6 and tumor necrosis factor-alpha

Infection by herpesviruses can result in profound immunosuppressive or immunomodulatory effects. However, no significant information is available on the effect of such infections on the production of immunoregulatory cytokines. We studied the kinetics of production of two monocyte-derived cytokines, interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF alpha), induced by Epstein-Barr virus (EBV) and herpes simplex virus type 1 (HSV-1) in peripheral blood mononuclear cell cultures and in fractionated cell populations. We observed that, when compared to HSV-1, EBV is a stronger inducer of IL-6. In EBV-infected cultures, IL-6 protein was detected at day 1 postinfection and gradually increased with time. In contrast, lower amounts of IL-6 were detected 5 d postinfection in HSV-1-infected cultures. HSV-1-infected cultures secreted significant amounts of TNF alpha protein after 5 d of culture and reached a maximal level of production at day 7, whereas EBV inhibited TNF alpha production. In fractionated cell populations, monocytic cells were found to be the main source of IL-6 synthesis after EBV or HSV-1 infection. However, TNF alpha synthesis in HSV-1-infected cultures was from both B and monocytic cells. By using the polymerase chain reaction technique we show that, after infection by these two herpesviruses, differences in cytokine gene products are also observed at the transcriptional level. These observations demonstrate that EBV and HSV-1 exert differential effects on IL-6 and TNF alpha gene transcription and on the resulting protein secretion in human mononuclear blood cells.