In vitro activity evaluation of Parkia pendula seed lectin against human cytomegalovirus and herpes virus 6.

Human cytomegalovirus (HCMV) in vitro infectivity was inhibited by Parkia pendula seed lectin (PpeL) in contrast to human herpes virus 6 (HHV-6) which was not affected. The antiviral activity was detected for HCMV in human embryo lung (HEL) cells using a microtechnique in culture plates. The assay showed a reduction of cellular infectivity from approximately 95%, at a concentration of 150microg/mL with minimal cytotoxicity (25%). Also, a reduction of 75% was observed in HEL cells at a concentration of 75microg/mL without toxic effect. The reduction on infectivity was observed even after virus pre-adsorption to cells suggesting that this action should occur after virus penetration, in the intracellular replication phase. MT4 lymphocytes and cord blood mononuclear cells (CBMC) were used to evaluate the lectin effect on HHV-6 following the same technique. Lectin concentrations with few or no toxic effects on lymphocytes did not show inhibitory action of HHV-6 cytopathic effect. The results obtained with PpeL demonstrate that it may have an impact in the design of pharmacological strategies to infection of cytomegalovirus.     

Antiviral activities and the mechanism of 9-beta-D-ribofuranosyl-6-alkylthiopurines on several RNA viruses from animals

A series of 9-beta-D-ribofuranosyl-6-alkylthiopurines (6-alkyl TI) were found to inhibit in vitro replication of infectious hematopoietic necrosis virus (IHNV), human influenza virus (IFV) and respiratory syncytial virus (RSV) with IC50 values of about 0.06 microgram/ml, 0.7-1.5 micrograms/ml and 1-3 micrograms/ml, respectively. Viral RNA synthesis in infected cells in the presence of actinomycin D was inhibited by treatment with the compounds dose-dependently. It was also found that the decrease of rNTP pool size in infected cells was remarkably dose-dependent. From these findings, the mode of antiviral action of these compounds may be explained by rNTP imbalance in the treated group.     

Role of IL-15 on monocytic resistance to human herpesvirus 6 infection

Interleukin-15 (IL-15) is a cytokine that possesses a variety of biological functions, including stimulation and maintenance of cellular immune responses. Recently, it has been demonstrated that Human Herpes virus type 6 (HHV-6) enhances NK activity of human PBMC by inducing IL-15. HHV-6 is a typical immunosuppressive agent, as suggested by its tropism for both CD4+ and CD8+ T cells, B cells, monocytes/macrophages, megakaryocytes and NK cells. Moreover, several studies have indicated that mononuclear phagocyte resistance to virus infection is influenced by the cellular differentiation state. This paper describes the effect of pretreatment "in vitro" with IL-15 on the resistance of human monocytes (HM) to HHV-6 infection. Our results demonstrate that undifferentiated HM were highly resistant to HHV-6 infection, whereas HM pretreated with human recombinant IL-15 showed an increased permissiveness for HHV-6 infection. This permissiveness was characterised by higher release of extracellular virus as well as an increased percentage of antigen positive cells. Moreover, we evaluated IL-15 production after the addition of HHV-6 to monocytes precultured in different experimental conditions. Our data indicate that HHV-6-induced IL-15 production by human monocytes is not affected by the condition of "in vitro" precultivation/differentiation. Furthermore, the neutralization of IL-15 induced by HHV-6 in differentiated monocytes did not affect viral replication. These findings suggest that IL-15 acts only on the mechanisms of cellular differentiation, rendering HM more susceptible to HHV-6 infection, without interfering with virus replication.     

A novel anti-HIV synthetic peptide, T-22 ([Tyr5,12,Lys7]-polyphemusin II).

Tachyplesin and polyphemusin are antimicrobial peptides recently isolated from the hemocytes of horseshoe crabs (Tachypleus tridentatus and Limulus polyphemus). We synthesized them and their analogs and examined their antiviral activity against human immunodeficiency virus (HIV) type 1 in vitro. The infection of human T cells with the virus was markedly inhibited by some of them at low concentrations. In this structure-activity study, we found that [Tyr5,12, Lys7]-polyphemusin II, which was designated as T22, had extremely high anti-HIV activity. Its 50% inhibitory concentration (EC50) was 0.008 micrograms/ml, while its 50% cytotoxic concentration (CC50) was 54 micrograms/ml and these values were comparable to those of AZT. This result indicates that T22 would be a potential candidate for the therapy of HIV infection.     

Susceptibility of human herpesvirus 6 to antiviral compounds by flow cytometry analysis

BACKGROUND: The emergence of human herpesvirus 6 (HHV-6) as a human pathogen led to the possibility of specific therapy against HHV-6 and the development of standardized susceptibility assays of HHV-6 to antivirals. METHODS: We have developed a flow cytometry method to analyze the multiplication of the HST strain of human herpesvirus 6 (HHV-6) variant B in vitro using monoclonal antibodies specific to virus proteins. This method was subsequently used to determine the sensitivity of HST multiplication in MT4 cells to four antiviral compounds of three different classes: acyclovir (ACV) and ganciclovir (GCV), two acyclic guanosine analogs; cedofovir (CDV), an acyclic nucleoside phosphonate; and phosphonoformic acid (PFA), a pyrophosphate analog. RESULTS: The 50% inhibitory concentrations (IC(50)) of ACV, GCV, CDV, and PFA determined by flow cytometry assay were 25.3, 6.4, 0.95, and 6.0 microM, respectively (5.7, 1.6, 0.3, and 1.8 microg/ml, respectively). These data together with the results of cytotoxicity assays confirmed the high efficiency and selectivity of CDV and PFA against HHV-6 B in vitro, suggested by previous results. CONCLUSIONS: Our flow cytometric assay appeared as a reproducible specific method to characterize HHV-6 susceptibility to antiviral compounds. It can be considered as a convenient alternative to the other immunologic and DNA hybridization assays used for that purpose.     

Inhibition of human immunodeficiency virus type 1 replication and cytopathicity by synthetic soluble catecholamine melanins in vitro

Synthetic soluble melanins were synthesized by spontaneous oxidation of L-dopamine, norepinephrine or 5-hydroxytryptamine (serotonin) in weak alkaline solution. These three melanins inhibited infection of human CD4+ lymphoblastoid cells (MT-2) by cell-free human immunodeficiency virus type 1 (HIV-1), without cell toxicity, at concentrations of 0.15-10 micrograms/ml. Also, syncytium formation and resulting cytopathic effects when uninfected cells were mixed with chronic HIV-1-infected cells were blocked by these melanins. Antisyncytial activity was greater when infected cells were preincubated with melanin than when uninfected cells were preincubated with melanin, thus suggesting that interaction of melanin with viral proteins is an important aspect of the antiviral mechanism. These results make synthetic soluble melanins interesting candidates for further study as possible anti-HIV-1 therapeutics.     

Human herpesvirus 6 infects dendritic cells and suppresses human immunodeficiency virus type 1 replication in coinfected cultures

Human herpesvirus 6 (HHV-6) has been implicated as a cofactor in the progressive loss of CD4(+) T cells observed in AIDS patients. Because dendritic cells (DC) play an important role in the immunopathogenesis of human immunodeficiency virus (HIV) disease, we studied the infection of DC by HHV-6 and coinfection of DC by HHV-6 and HIV. Purified immature DC (derived from adherent peripheral blood mononuclear cells in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4) could be infected with HHV-6, as determined by PCR analyses, intracellular monoclonal antibody staining, and presence of virus in culture supernatants. However, HHV-6-infected DC demonstrated neither cytopathic changes nor functional defects. Interestingly, HHV-6 markedly suppressed HIV replication and syncytium formation in coinfected DC cultures. This HHV-6-mediated anti-HIV effect was DC specific, occurred when HHV-6 was added either before or after HIV, and was not due to decreased surface expression or function of CD4, CXCR4, or CCR5. Conversely, HIV had no demonstrable effect on HHV-6 replication. These findings suggest that HHV-6 may protect DC from HIV-induced cytopathicity in AIDS patients. We also demonstrate that interactions between HIV and herpesviruses are complex and that the observable outcome of dual infection is dependent on the target cell type.     

Human herpesvirus 6 infection of CD4+ T-cell subsets

The immune system includes CD4+ regulatory T (T reg) cells that play a role in self-tolerance and demonstrate functional variations that govern immune responses. HHV-6 is an important immunosuppressive virus that completely replicates in vivo and in vitro in only CD4+ T cells. However, there have been no reports of the specific T-cell subpopulation that permits the replication of this virus. Here, we evaluated the infectivity of HHV-6 to specific T-cell populations such as CD4+CD25 high, which includes the majority of T reg cells, and CD4+CD25(-). These cells were isolated from peripheral blood and then expanded. The expanded cell fractions were then infected with the HHV-6 variant B strain, and the spreads of infected cells were evaluated by immunofluorescence. Viral growth was also quantified by real-time PCR. The effects of virus infection on cytokine production from these T-cell subsets were examined using ELISA. Our results revealed that both these fractions permitted complete HHV-6 replication. Virus infection enhanced the production of both Th1- and Th2-type cytokines from CD4+CD25(-) T cells; however, only Th2-type cytokine release was augmented from viral-infected CD4+CD25 high T cells. Further, while virusinfected CD4+CD25 high T cells shift their antiviral immunity toward Th2 dominance by producing IL-10, the role of virus-infected CD4+CD25(-) T cells remains obscure.     

Mechanism of inhibition of HIV-1 infection in vitro by guanine-rich oligonucleotides modified at the 5' terminal by dimethoxytrityl residue.

Oligodeoxyribonucleotides (ODN) linked at their 5'-end with dimethoxytrityl (DmTr) residue were examined for antiviral activities against human immunodeficiency virus type 1 (HIV-1). We found that guanine-rich oligonucleotides exhibit anti-HIV activity upon 5'-end modification with DmTr. One oligonucleotide, DmTr-TGGGAGGTGGGTCTG (SA-1042), showed potent anti-HIV activity in vitro. A greater than 95% reduction of infectivity was observed if the cells were treated with 10 micrograms/ml of SA-1042 at the time of viral infection, PCR analysis confirmed that there was a significant reduction of provirus in the cells exposed to virus in the presence of SA-1042. By contrast, no inhibition was observed if the cells were treated with the oligomer 1 h after virus adsorption. SA-1042 prevented syncytium formation between chronically infected cells and CD4 positive uninfected cells. Furthermore, the oligomer interfered the interaction of purified gp120 to the CD4 receptor. By contrast, SA-1042 had no inhibitory effect on chronically HIV-infected cells. These results strongly suggest that the DMTr-ODNs with appropriate base sequences antagonize HIV-1 infection during the stage of virus-cell interaction.     

Focus formation by the human immunodeficiency virus (HIV) in the immobilized MT-4 cell culture and its application to the evaluation of anti-HIV agents.

Immunofluorescence studies were performed on the infection of monolayer cultures of immobilized MT-4 cells with human immunodeficiency virus type 1 (HIV-1). By using the anti-viral p24 monoclonal antibody, we could observe formation of foci of p24 antigen-positive cells within 3 to 4 days when the infection was initiated with a relatively small amount of the virus. Frequency of the focus formation was in proportion to the dose of input virus (ranging from 0.001 to 0.1 PFU/cell), which allowed us to apply this phenomenon to the assay of anti-HIV agents as well as to the estimation of relative infectivity of the virus stocks. When antiviral agents were added to the infected cultures, number of foci as well as the size of each focus was reduced in a concentration-dependent manner. The dose required for reducing the number of foci by 50% was calculated to be 6 ng/ml and 8 ng/ml for tunicamycin (TM) and azidothymidine (AZT), respectively. These values are comparable to those obtained by other current assay methods. In addition, focus reduction assay is also useful in searching for such antiviral agents that would inhibit or block the early step of viral replication cycle.     

GP96 Interacts with HHV-6 during Viral Entry and Directs It for Cellular Degradation

CD46 and CD134 mediate attachment of Human Herpesvirus 6A (HHV-6A) and HHV-6B to host cell, respectively. But many cell types interfere with viral infection through rapid degradation of viral DNA. Hence, not all cells expressing these receptors are permissive to HHV-6 DNA replication and production of infective virions suggesting the involvement of additional factors that influence HHV-6 propagation. Here, we used a proteomics approach to identify other host cell proteins necessary for HHV-6 binding and entry. We found host cell chaperone protein GP96 to interact with HHV-6A and HHV-6B and to interfere with virus propagation within the host cell. In human peripheral blood mononuclear cells (PBMCs), GP96 is transported to the cell surface upon infection with HHV-6 and interacts with HHV-6A and -6B through its C-terminal end. Suppression of GP96 expression decreased initial viral binding but increased viral DNA replication. Transient expression of human GP96 allowed HHV-6 entry into CHO-K1 cells even in the absence of CD46. Thus, our results suggest an important role for GP96 during HHV-6 infection, which possibly supports the cellular degradation of the virus.     

Efficient propagation of human herpesvirus 6B in a T-cell line derived from a patient with adult T-cell leukemia/lymphoma.

The efficient propagation of the OK strain of the B variant of human herpesvirus 6 (HHV-6B) was demonstrated in a line of T cells, TaY, established from the peripheral blood lymphocytes of a patient with adult T-cell leukemia/lymphoma (ATL). Growth of TaY cells depends on the presence of IL-2 and the cells harbor HTLV-I genomes. A severe cytopathic effect (CPE) was observed in many HHV-6B(OK)-infected TaY cells one week after infection. The release of virus from HHV-6B(OK)-infected TaY cells [TaY(OK)] was first detected after three days and increased rapidly for up to seven days after infection, as demonstrated by PCR. The titer of HHV-6B(OK) in the supernatant was comparable to the value of 10(3.5) TCID50/ml obtained with PHA-activated cord blood lymphocytes (CBL) that had been infected with HHV-6B(OK). The replication of the virus was shown to depend to a considerable extent on cell viability. Electron microscopy revealed many herpesvirus-type capsid- and enveloped-viruses in the nuclei and cytoplasm of degenerated cells in TaY(OK) cultures. The U1102 strain of HHV-6A and the Z29 strain of HHV-6B also infected TaY cells productively, as detected by PCR and an immunofluorescence test. These results suggest that the activation of CD4+ T lymphocytes with mitogens such as PHA or IL-2 and the expression of some cellular gene or the HTLV-I gene might be essential for efficient propagation of HHV-6B. TaY cells should play an important role in future investigations of cell-virus interactions and genetic variations or cell tropism of HHV-6 isolates since no cell line that shows propagation of both HHV-6A and HHV-6B has been reported to date.     

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.     

In vitro anti-human immunodeficiency virus activity of polysaccharide from Rhizophora mucronata Poir.

A polysaccharide was extracted with 1% sodium carbonate from the bark of Rhizophora mucronata and its antiviral activities against human immunodeficiency virus (HIV) were assessed by an in vitro cell culture system. The anti-HIV activity of the alkaline extract was mainly recovered in the 25-75% ethanol-precipitated fraction. Rhizophora mucronata polysaccharide (RMP) protected MT-4 cells from the HIV-induced cytopathogenicity and blocked the expression of HIV antigens. RMP completely inhibited the viral binding to the cell and the formation of syncytium upon cocultivation of MOLT-4/HIV-1IIIB cells and MOLT-4 cells. These results suggest that RMP inhibited early steps of the virus life cycle especially virus adsorption to the cell.     

A biological response modifier, PSK, inhibits human immunodeficiency virus infection in vitro

PSK, a biological response modifier (BRM), was studied to determine its anti-viral activity on human immunodeficiency virus (HIV) in vitro. Either a novel infection system using human T-cell lymphotropic virus type I (HTLV-I)-carrying MT-4 cells or a coculture system using MOLT-4 cells and its virus-producing cells MOLT-4/HIVHTLV-IIIB which induces multinucleated giant cells very efficiently was used. PSK almost completely blocked the cytopathic effect such as giant cell formation and HIV-specific antigen expression both in MT-4 cells and MOLT-4 cells at a concentration of 0.4 and 0.8 mg/ml, respectively. Pretreatment of the virus with PSK may specifically interfere with early stages of HIV infection by modifying the viral receptor.     

Bicyclams, Selective Antagonists of the Human Chemokine Receptor CXCR4, Potently Inhibit Feline Immunodeficiency Virus Replication

Bicyclams are low-molecular-weight anti-human immunodeficiency virus (HIV) agents that have been shown to act as potent and selective CXC chemokine receptor 4 (CXCR4) antagonists. Here, we demonstrate that bicyclams are potent inhibitors of feline immunodeficiency virus (FIV) replication when evaluated in Crandell feline kidney (CRFK) cells. With a series of bicyclam derivatives, 50% inhibitory concentrations (IC50s) against FIV were obtained in this cell system that were comparable to those obtained for HIV-1 IIIB replication in the human CD4(+) MT-4 T-cell line. The bicyclams were also able to block FIV replication in feline thymocytes, albeit at higher concentrations than in the CRFK cells. The prototype bicyclam AMD3100, 1-1'-[1,4-phenylene-bis(methylene)]-bis(1,4,8, 11-tetraazacyclotetradecane), was only fourfold less active in feline thymocytes (IC50, 62 ng/ml) than in CRFK cells (IC50, 14 ng/ml). AMD2763, 1,1'-propylene-bis(1,4,8, 11-tetraazacyclotetradecane), which is a less potent CXCR4 antagonist, was virtually inactive against FIV in feline thymocytes (IC50, >66.5 microgram/ml), while it was clearly active in CRFK cells (IC50, 0.9 microgram/ml). The CXC chemokine stromal-cell-derived factor 1alpha had anti-FIV activity in CRFK cells (IC50, 200 ng/ml) but not in feline thymocytes (IC50, >2.5 microgram/ml). When primary FIV isolates were evaluated for their drug susceptibility in feline thymocytes, the bicyclams AMD3100 and its Zn2+ complex, AMD3479, inhibited all six primary isolates at equal potency. The marked susceptibility of FIV to the bicyclams suggests that FIV predominantly uses feline CXCR4 for entering its target cells.