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.