Glycoprotein gE of herpes simplex virus type 1: effects of anti-gE on virion infectivity and on virus-induced fc-binding receptors

Suppression of annexin A1 and its receptor reduces herpes simplex virus 1 lethality in mice

Herpes simplex virus 1 (HSV-1)-induced encephalitis is the most common cause of sporadic, fatal encephalitis in humans. HSV-1 has at least 10 different envelope glycoproteins, which can promote virus infection. The ligands for most of the envelope glycoproteins and the significance of these ligands in virus-induced encephalitis remain elusive. Here, we show that glycoprotein E (gE) binds to the cellular protein, annexin A1 (Anx-A1) to enhance infection. Anx-A1 can be detected on the surface of cells permissive for HSV-1 before infection and on virions. Suppression of Anx-A1 or its receptor, formyl peptide receptor 2 (FPR2), on the cell surface and gE or Anx-A1 on HSV-1 envelopes reduced virus binding to cells. Importantly, Anx-A1 knockout, Anx-A1 knockdown, or treatments with the FPR2 antagonist reduced the mortality and tissue viral loads of infected mice. Our results show that Anx-A1 is a novel enhancing factor of HSV-1 infection. Anx-A1-deficient mice displayed no evident physiology and behavior changes. Hence, targeting Anx-A1 and FPR2 could be a promising prophylaxis or adjuvant therapy to decrease HSV-1 lethality.

Herpes simplex virus 1 (HSV-1)-induced encephalitis is the most devastating consequence of HSV-1 infection, even in patients treated with anti-HSV-1 drugs. Moreover, encephalitis induced by drug-resistant HSV-1 has been reported in immunocompromised patients. Identifying the cellular factors in promoting HSV-1 replication, especially those increasing virus attachment and entry, could facilitate the development of alternative or adjuvant therapy. Here, we identified annexin A1 (Anx-A1) and its receptor, formyl peptide receptor 2 (FPR2), facilitating HSV-1 attachment to the cell surface. Suppression of Anx-A1 or blockage of FPR2 impaired HSV-1 attachment to cells, viral yields in cells, and HSV-1 lethality in mice. Moreover, blocking FPR2 decreased the replication of drug-resistant HSV-1 in BABL/c nude mice. Hence, targeting Anx-A1 and FPR2 could be alternative or adjuvant therapy for HSV-1 infection.

Viral infection of human neurons triggers strain-specific differences in host neuronal and viral transcriptomes

Infection with herpes simplex virus 1 (HSV-1) occurs in over half the global population, causing recurrent orofacial and/or genital lesions. Individual strains of HSV-1 demonstrate differences in neurovirulence in vivo, suggesting that viral genetic differences may impact phenotype. Here differentiated SH-SY5Y human neuronal cells were infected with one of three HSV-1 strains known to differ in neurovirulence in vivo. Host and viral RNA were sequenced simultaneously, revealing strain-specific differences in both viral and host transcription in infected neurons. Neuronal morphology and immunofluorescence data highlight the pathological changes in neuronal cytoarchitecture induced by HSV-1 infection, which may reflect host transcriptional changes in pathways associated with adherens junctions, integrin signaling, and others. Comparison of viral protein levels in neurons and epithelial cells demonstrated that a number of differences were neuron-specific, suggesting that strain-to-strain variations in host and virus transcription are cell type-dependent. Together, these data demonstrate the importance of studying virus strain- and cell-type-specific factors that may contribute to neurovirulence in vivo, and highlight the specificity of HSV-1-host interactions.

Protection from lethal herpes simplex virus type 1 infection by vaccination with a UL41-deficient recombinant strain

The UL41 gene of herpes simplex virus type 1 (HSV-1) encodes a virion host shut off protein which is involved in immune evasion.　The growth and virulence of HSV-1 is markedly reduced by the deletion of UL41.　In this report, the UL41-deleted recombinant HSV-1 strain VR∆41 was evaluated as a prophylactic live attenuated vaccine against lethal HSV-1 infection in a mouse model.　Intraperitoneal (i.p.) inoculation with the VR∆41 strain clearly inhibited lethal wild-type HSV-1 (VR-3 strain) infection after both i.p. and intracerebral (i.c.) inoculations.　Vaccination with the VR∆41 strain was safer than VR-3 vaccination and was able to protect against a wild-type challenge to the same degree as VR-3 vaccination.　In contrast, i.p. inoculation with ultraviolet-irradiated VR-3 induced resistance against i.p. infection, but not against i.c.

INFECTION

Although replication of the VR∆41 strain in mice was greatly reduced compared to that of the VR-3 strain, VR∆41 strain maintained the ability to spread to the central nervous system (CNS) from a peripheral inoculation site. These results indicated that the VR∆41 strain evoked a potent immune reaction through viral protein expression within CNS without the induction of lethal encephalitis.　The entry of antigens into the CNS was essential for the establishment of protective immunity against the lethal HSV encephalitis.　We concluded that only a live attenuated vaccine is able to afford a prophylactic effect against CNS infection with HSV.　In order to fulfill this requirement, UL41-deleted viruses provide a strong candidate for use as a recombinant live vaccine.

Cellular Protein WDR11 Interacts with Specific Herpes Simplex Virus Proteins at the trans-Golgi Network To Promote Virus Replication

It has recently been proposed that the herpes simplex virus (HSV) protein ICP0 has cytoplasmic roles in blocking antiviral signaling and in promoting viral replication in addition to its well-known proteasome-dependent functions in the nucleus. However, the mechanisms through which it produces these effects remain unclear. While investigating this further, we identified a novel cytoplasmic interaction between ICP0 and the poorly characterized cellular protein WDR11. During an HSV infection, WDR11 undergoes a dramatic change in localization at late times in the viral replication cycle, moving from defined perinuclear structures to a dispersed cytoplasmic distribution. While this relocation was not observed during infection with viruses other than HSV-1 and correlated with efficient HSV-1 replication, the redistribution was found to occur independently of ICP0 expression, instead requiring viral late gene expression. We demonstrate for the first time that WDR11 is localized to the trans-Golgi network (TGN), where it interacts specifically with some, but not all, HSV virion components, in addition to ICP0. Knockdown of WDR11 in cultured human cells resulted in a modest but consistent decrease in yields of both wild-type and ICP0-null viruses, in the supernatant and cell-associated fractions, without affecting viral gene expression. Although further study is required, we propose that WDR11 participates in viral assembly and/or secondary envelopment.

IMPORTANCE

While the TGN has been proposed to be the major site of HSV-1 secondary envelopment, this process is incompletely understood, and in particular, the role of cellular TGN components in this pathway is unknown. Additionally, little is known about the cellular functions of WDR11, although the disruption of this protein has been implicated in multiple human diseases. Therefore, our finding that WDR11 is a TGN-resident protein that interacts with specific viral proteins to enhance viral yields improves both our understanding of basic cellular biology as well as how this protein is co-opted by HSV.

The herpes simplex virus 1 IgG fc receptor blocks antibody-mediated complement activation and antibody-dependent cellular cytotoxicity in vivo

Herpes simplex virus 1 (HSV-1) glycoprotein E (gE) mediates cell-to-cell spread and functions as an IgG Fc receptor (FcγR) that blocks the Fc domain of antibody targeting the virus or infected cell. Efforts to assess the functions of the HSV-1 FcγR in vivo have been hampered by difficulties in preparing an FcγR-negative strain that is relatively intact for spread. Here we report the FcγR and spread phenotypes of NS-gE264, which is a mutant strain that has four amino acids inserted after gE residue 264. The virus is defective in IgG Fc binding yet causes zosteriform disease in the mouse flank model that is only minimally reduced compared with wild-type and the rescue strains. The presence of zosteriform disease suggests that NS-gE264 spread functions are well maintained. The HSV-1 FcγR binds the Fc domain of human, but not murine IgG; therefore, to assess FcγR functions in vivo, mice were passively immunized with human IgG antibody to HSV. When antibody was inoculated intraperitoneally 20 h prior to infection or shortly after virus reached the dorsal root ganglia, disease severity was significantly reduced in mice infected with NS-gE264, but not in mice infected with wild-type or rescue virus. Studies of C3 knockout mice and natural killer cell-depleted mice demonstrated that the HSV-1 FcγR blocked both IgG Fc-mediated complement activation and antibody-dependent cellular cytotoxicity. Therefore, the HSV-1 FcγR promotes immune evasion from IgG Fc-mediated activities and likely contributes to virulence at times when antibody is present, such as during recurrent infections.

Antagonism of the complement component C4 by flavivirus nonstructural protein NS1

The complement system plays an essential protective role in the initial defense against many microorganisms. Flavivirus NS1 is a secreted nonstructural glycoprotein that accumulates in blood, is displayed on the surface of infected cells, and has been hypothesized to have immune evasion functions. Herein, we demonstrate that dengue virus (DENV), West Nile virus (WNV), and yellow fever virus (YFV) NS1 attenuate classical and lectin pathway activation by directly interacting with C4. Binding of NS1 to C4 reduced C4b deposition and C3 convertase (C4b2a) activity. Although NS1 bound C4b, it lacked intrinsic cofactor activity to degrade C4b, and did not block C3 convertase formation or accelerate decay of the C3 and C5 convertases. Instead, NS1 enhanced C4 cleavage by recruiting and activating the complement-specific protease C1s. By binding C1s and C4 in a complex, NS1 promotes efficient degradation of C4 to C4b. Through this mechanism, NS1 protects DENV from complement-dependent neutralization in solution. These studies define a novel immune evasion mechanism for restricting complement control of microbial infection.

Virion incorporation of the herpes simplex virus type 1 tegument protein VP22 occurs via glycoprotein E-specific recruitment to the late secretory pathway

The mechanism by which herpesviruses acquire their tegument is not yet clear. One model is that outer tegument proteins are recruited by the cytoplasmic tails of viral glycoproteins. In the case of herpes simplex virus tegument protein VP22, interactions with the glycoproteins gE and gD have been shown. We have previously shown that the C-terminal half of VP22 contains the necessary signal for assembly into the virus. Here, we show that during infection VP22 interacts with gE and gM, as well as its tegument partner VP16. However, by using a range of techniques we were unable to demonstrate VP22 binding to gD. By using pulldown assays, we show that while the cytoplasmic tails of both gE and gM interact with VP22, only gE interacts efficiently with the C-terminal packaging domain of VP22. Furthermore, gE but not gM can recruit VP22 to the Golgi/trans-Golgi network region of the cell in the absence of other virus proteins. To examine the role of the gE-VP22 interaction in infection, we constructed a recombinant virus expressing a mutant VP22 protein with a 14-residue deletion that is unable to bind gE (Delta gEbind). Coimmunoprecipitation assays confirmed that this variant of VP22 was unable to complex with gE. Moreover, VP22 was no longer recruited to its characteristic cytoplasmic trafficking complexes but exhibited a diffuse localization. Importantly, packaging of this variant into virions was abrogated. The mutant virus exhibited poor growth in epithelial cells, similar to the defect we have observed for a VP22 knockout virus. These results suggest that deletion of just 14 residues from the VP22 protein is sufficient to inhibit binding to gE and hence recruitment to the viral envelope and assembly into the virus, resulting in a growth phenotype equivalent to that produced by deleting the entire reading frame.

ICP22 is required for wild-type composition and infectivity of herpes simplex virus type 1 virions

The immediate-early regulatory protein ICP22 is required for efficient replication of herpes simplex virus type 1 in some cell types (permissive) but not in others (restrictive). In mice infected via the ocular route, the pathogenesis of an ICP22- virus, 22/n199, was altered relative to that of wild-type virus. Specifically, tear film titers of 22/n199-infected mice were significantly reduced at 3 h postinfection relative to those of mice infected with wild-type virus. Further, 22/n199 virus titers were below the level of detection in trigeminal ganglia (TG) during the first 9 days postinfection. On day 30 postinfection, TG from 22/n199-infected mice contained reduced viral genome loads and exhibited reduced expression of latency-associated transcripts and reduced reactivation efficiency relative to TG from wild-type virus-infected mice. Notably, the first detectable alteration in the pathogenesis of 22/n199 in these tests occurred in the eye prior to the onset of nascent virus production. Thus, ICP22- virions appeared to be degraded, cleared, or adsorbed more rapidly than wild-type virions, implying potential differences in the composition of the two virion types. Analysis of the protein composition of purified extracellular virions indicated that ICP22 is not a virion component and that 22/n199 virions sediment at a reduced density relative to wild-type virions. Although similar to wild-type virions morphologically, 22/n199 virions contain reduced amounts of two gamma2 late proteins, US11 and gC, and increased amounts of two immediate-early proteins, ICP0 and ICP4, as well as protein species not detected in wild-type virions. Although ICP22- viruses replicate to near-wild-type levels in permissive cells, the virions produced in these cells are biochemically and physically different from wild-type virions. These virion-specific differences in ICP22- viruses add a new level of complexity to the functional analysis of this immediate-early viral regulatory protein.

The extracellular domain of herpes simplex virus gE is indispensable for efficient cell-to-cell spread: evidence for gE/gI receptors

Herpes simplex virus (HSV) spreads rapidly and efficiently within epithelial and neuronal tissues. The HSV glycoprotein heterodimer gE/gI plays a critical role in promoting cell-to-cell spread but does not obviously function during entry of extracellular virus into cells. Thus, gE/gI is an important molecular handle on the poorly understood process of cell-to-cell spread. There was previous evidence that the large extracellular (ET) domains of gE/gI might be important in cell-to-cell spread. First, gE/gI extensively accumulates at cell junctions, consistent with being tethered there. Second, expression of gE/gI in trans interfered with HSV spread between epithelial cells. To directly test whether the gE ET domain was necessary for gE/gI to promote virus spread, a panel of gE mutants with small insertions in the ET domain was constructed. Cell-to-cell spread was reduced when insertions were made within either of two regions, residues 256 to 291 or 348 to 380. There was a strong correlation between loss of cell-to-cell spread function and binding of immunoglobulin. gE ET domain mutants 277, 291, and 348 bound gI, produced mature forms of gE that reached the cell surface, and were incorporated into virions yet produced plaques similar to gE null mutants. Moreover, all three mutants were highly restricted in spread within the corneal epithelium, in the case of mutant 277 to only 4 to 6% of the number of cells compared with wild-type HSV. Therefore, the ET domain of gE is indispensable for efficient cell-to-cell spread. These observations are consistent with our working hypothesis that gE/gI can bind extracellular ligands, so-called gE/gI receptors that are concentrated at epithelial cell junctions. This fits with similarities in structure and function of gE/gI and gD, which is a receptor binding protein.

Virus complement evasion strategies

The immune system has a variety of tools at its disposal to combat virus infections. These can be subdivided roughly into two categories: 'first line defence', consisting of the non-specific, innate immune system, and 'adaptive immune response', acquired over time following virus infection or vaccination. During evolution, viruses have developed numerous, and often very ingenious, strategies to counteract efficient recognition of virions or virus-infected cells by both innate and adaptive immunity. This review will focus on the different strategies that viruses use to avoid recognition by one of the components of the immune system: the complement system. Complement evasion is of particular importance for viruses, since complement activation is a crucial component of innate immunity (alternative and mannan-binding lectin activation pathway) as well as of adaptive immunity (classical, antibody-dependent complement activation).

Herpes simplex virus type 1 evades the effects of antibody and complement in vivo

Herpes simplex virus type 1 (HSV-1) encodes a complement-interacting glycoprotein, gC, and an immunoglobulin G (IgG) Fc binding glycoprotein, gE, that mediate immune evasion by affecting multiple aspects of innate and acquired immunity, including interfering with complement components C1q, C3, C5, and properdin and blocking antibody-dependent cellular cytotoxicity. Previous studies evaluated the individual contributions of gC and gE to immune evasion. Experiments in a murine model that examines the combined effects of gC and gE immune evasion on pathogenesis are now reported. Virulence of wild-type HSV-1 is compared with mutant viruses defective in gC-mediated C3 binding, gE-mediated IgG Fc binding, or both immune evasion activities. Eliminating both activities greatly increased susceptibility of HSV-1 to antibody and complement neutralization in vitro and markedly reduced virulence in vivo as measured by disease scores, virus titers, and mortality. Studies with C3 knockout mice indicated that other activities attributed to these glycoproteins, such as gC-mediated virus attachment to heparan sulfate or gE-mediated cell-to-cell spread, do not account for the reduced virulence of mutant viruses. The results support the importance of gC and gE immune evasion in vivo and suggest potential new targets for prevention and treatment of HSV disease.

The role of the UL41 gene of herpes simplex virus type 1 in evasion of non-specific host defence mechanisms during primary infection

The UL41 gene product (vhs) of herpes simplex virus (HSV) is packaged in the virion, and mediates host protein synthesis shutoff at the early stage of the virus replication cycle. In order to clarify the role of vhs in virus replication and virulence, we isolated a completely UL41-deficient mutant (the VRDelta41 strain) and its revertant (the VRDelta41R strain). In the mouse encephalitis model, the replication of strain VRDelta41 was inhibited after 2 days post-infection, resulting in low virulence, by gamma-ray-sensitive cells such as lymphocytes and/or neutrophils. The result suggested that some cytokines, produced in VRDelta41-inoculated brains, activate and induce the migration of gamma-ray-sensitive cells to the infection site. Therefore, cytokines produced by HSV-1-infected human cells were screened, and potent inductions of interleukin (IL)-1beta, IL-8 and macrophage inflammatory protein-1alpha by VRDelta41 infection were observed. Moreover, the VRDelta41 strain showed 20- and 5-fold higher sensitivity to interferon-alpha and -beta compared to the wild-type strain, respectively. These results indicate that one important role of vhs in vivo is evasion from non-specific host defence mechanisms during primary infection through suppression of cytokine production in HSV-infected cells and reduction of the anti-HSV activity of interferon-alpha and -beta.

The C-terminal cytoplasmic tail of herpes simplex virus type 1 gE protein is phosphorylated in vivo and in vitro by cellular enzymes in the absence of other viral proteins

Herpes simplex virus 1 glycoprotein E (gE-1) is highly phosphorylated in culture cells during infection. In this report, it is shown that phosphorylation is mediated by host enzymes in human cells stably transfected with gE, in the absence of other herpesvirus products. In contrast, a tailless gE product (C terminus deletion mutant) is not phosphorylated. By using an in vitro kinase assay combined with linker-insertion mutagenesis, it is shown that casein kinase II catalyses the phosphorylation of the C-terminal domain of the protein. Also, it is demonstrated that the serine residues at positions 476 and/or 477 in the cytoplasmic portion of the protein are the major acceptors for the phosphate groups.

The herpes simplex virus gE-gI complex facilitates cell-to-cell spread and binds to components of cell junctions

The herpes simplex virus (HSV) glycoprotein complex gE-gI mediates the spread of viruses between adjacent cells, and this property is especially evident for cells that form extensive cell junctions, e.g., epithelial cells, fibroblasts, and neurons. Mutants lacking gE or gI are not compromised in their ability to enter cells as extracellular viruses. Therefore, gE-gI functions specifically in the movement of virus across cell-cell contacts and, as such, provides a molecular handle on this poorly understood process. We expressed gE-gI in human epithelial cells by using replication-defective adenovirus (Ad) vectors. gE-gI accumulated at lateral surfaces of the epithelial cells, colocalizing with the adherens junction protein beta-catenin but was not found on either the apical or basal plasma membranes and did not colocalize with ZO-1, a component of tight junctions. In subconfluent monolayers, gE-gI was found at cell junctions but was absent from those lateral surfaces not in contact with another cell, as was the case for beta-catenin. Similar localization of gE-gI to cell junctions was observed in HSV-infected epithelial cells. By contrast, HSV glycoprotein gD, expressed using a recombinant Ad vectors, was found primarily along the apical surfaces of cells, with little or no protein found on the basal or lateral surfaces. Expression of gE-gI without other HSV polypeptides did not cause redistribution of either ZO-1 or beta-catenin or alter tight-junction functions. Together these results support a model in which gE-gI accumulates at sites of cell-cell contact by interacting with junctional components. We hypothesize that gE-gI mediates transfer of HSV across cell junctions by virtue of these interactions with cell junction components.

UL13 protein kinase of herpes simplex virus 1 complexes with glycoprotein E and mediates the phosphorylation of the viral Fc receptor: glycoproteins E and I

Herpes simplex virus 1 encodes a Fc receptor consisting of glycoproteins E (gE) and I (gI) and two protein kinases specified by UL13 and US3, respectively. We report the following: (i) Antibody to UL13 formed immune complexes containing gE and gI in addition to UL13 protein. Immune complexes formed by monoclonal antibody to gE, but not those formed by monoclonal antibody to gI, also contained the UL13 protein. This association may reflect direct interaction between gE and UL13 inasmuch as IgG in preimmune rabbit serum and an antiserum made against another viral protein which does not react with the UL13 protein directly also bound gE and UL13. (ii) In cells infected with the wild-type virus, gE formed two sharp bands and a diffuse, slower migrating band. The slower sharp band was undetectable, and the diffuse slower migrating forms of gE were diminished in lysates of cells infected with a mutant virus lacking the UL13 gene (DeltaUL13). (iii) Both gE and gI were labeled with 32Pi in cells infected with wild-type or the DeltaUL13 virus, but the labeling was significantly stronger in cells infected with the wild-type virus than in those infected with the DeltaUL13 virus. (iv) In an in vitro protein kinase assay, UL13 immunoprecipitated from cells infected with wild-type virus labeled gE in the presence of [gamma-32P]ATP. This activity was absent in precipitates from cells infected with DeltaUL13 virus. The labeled gE comigrated with the slower, sharp band of gE. (v) gI present in the UL13 immune complex was also phosphorylated in the in vitro kinase assay. (vi) The cytoplasmic domain of gE contains recognition sequences for phosphorylation by casein kinase II (CKII). Exogenous CKII phosphorylated gE in immune complexes from lysates of cells infected with the DeltaUL13 mutant or in immune complexes from lysates of cells infected with wild-type virus that had been heated to inactivate all endogenous kinase activity including that of UL13. In both instances, CKII phosphorylated gE in both the slow and fast migrating sharp bands. We conclude that UL13 physically associates with gE and mediates the phosphorylation of gE and gI. UL13 may also be a determinant in posttranslational processing of gE.

Human interferon reduces surface expression but not total production of herpes simplex virus type 1 glycoproteins gC and gE in heterologous hamster cells

The effect of interferon (IFN) on herpes simplex virus type 1 (HSV-1)-induced glycoproteins gC and gE was investigated in a heterologous IFN/cell model. In this model, the effect on surface expression of the glycoproteins could be studied separately from the effect on virus multiplication. Pretreatment of baby hamster kidney cells (BHK) with heterologous human leukocyte IFN suppressed surface expression of HSV-1-encoded gC and gE but had no influence on total production of the glycoproteins. This was in contrast to the effect on human embryonic fibroblast cells (HE) (homologous IFN and cells), where surface expression as well as total production of glycoproteins were reduced. The surface expression was demonstrated by antibody-sensitized monodisperse polystyrene beads, and immunoblotting and two-dimensional electrophoretic analysis of radioisotope-labeled proteins were used to study the total production.

Molecular mimicry between Fc receptor and S peplomer protein of mouse hepatitis virus, bovine corona virus, and transmissible gastroenteritis virus

We have previously demonstrated molecular mimicry between the S peplomer protein of mouse hepatitis virus (MHV) and Fc gamma R (Fc gamma R). A monoclonal antibody (MAb) to mouse Fc gamma R (2.4G2 anti-Fc gamma R MAb), purified rabbit immunoglobulin, but not their F(ab')2 fragments, as well as mouse and rat IgG, immunoprecipitated (1) recombinant S peplomer protein expressed by a vaccinia virus recombinant in human, rabbit, and mouse cells, and (2) natural S peplomer protein from cells infected with several strains of MHV and MHV escaped mutants. We report here results of studies documenting molecular mimicry between Fc gamma R and S peplomer protein of viruses representing three distinct antigenic subgroups of the Coronaviridae. We have shown a molecular mimicry between the S peplomer protein of bovine corona virus (BCV) and Fc gamma R. The 2.4G2 anti-Fc gamma R MAb, rabbit IgG, but not its F(ab')2 fragments, as well as homologous bovine serum, free of anti-BCV antibodies, immunoprecipitated S peplomer protein of BCV (Mebus strain). In contrast, we did not find molecular mimicry between S peplomer protein of human corona virus (HCV-OC43) and Fc gamma R. Although the OC43 virus belongs to the same antigenic group as MHV and BCV, MAb specific for human Fc gamma RI or Fc gamma RII and purified human IgG1, IgG2, and IgG3 myeloma proteins did not immunoprecipitate the S peplomer protein from HCV-OC43-infected RD cells. In addition, we did demonstrate molecular mimicry between the S peplomer protein of porcine transmissible gastroenteritis virus (TGEV) and Fc gamma R. TGEV belongs to the second antigenic subgroup of coronaviridae.(ABSTRACT TRUNCATED AT 250 WORDS)

The herpes simplex virus type 1 particle: structure and molecular functions. Review article

This review is a summary of our present knowledge with respect to the structure of the virion of herpes simplex virus type 1. The virion consists of a capsid into which the DNA is packaged, a tegument and an external envelope. The protein compositions of the structures outside the genome are described as well as the functions of individual proteins. Seven capsid proteins are identified, and two of them are mainly present in precursors of mature DNA-containing capsids. The protein components of the 150 hexamers and 12 pentamers in the icosahedral capsid are known. These capsomers all have a central channel and are connected by Y-shaped triplexes. In contrast to the capsid, the tegument has a less defined structure in which 11 proteins have been identified so far. Most of them are phosphorylated. Eleven virus-encoded glycoproteins are present in the envelope, and there may be a few more membrane proteins not yet identified. Functions of these glycoproteins include attachment to and penetration of the cellular membrane. The structural proteins, their functions, coding genes and localizations are listed in table form.

Characterization of baculovirus-expressed herpes simplex virus type 1 glycoprotein K

The DNA region encoding the complete herpes simplex virus type 1 (HSV-1) glycoprotein K (gK) was inserted into a baculovirus transfer vector, and recombinant viruses expressing gK were isolated. Four gK-related recombinant baculovirus-expressed peptides of 29, 35, 38, and 40 kDa were detected with polyclonal antibody to gK. The 35-, 38-, and 40-kDa species were susceptible to tunicamycin treatment, suggesting that they were glycosylated. The 38- and 40-kDa species corresponded to partially glycosylated precursor gK (pgK) and mature gK, respectively. The 29-kDa peptide probably represented a cleaved, unglycosylated peptide. The 35-kDa peptide probably represented a cleaved, glycosylated peptide that may be a precursor to pgK. Indirect immunofluorescence with polyclonal antibody to gK peptides indicated that the recombinant baculovirus-expressed gK was abundant on the surface of the insect cells in which it was expressed. Mice vaccinated with the baculovirus-expressed gK produced very low levels (< 1:10) of HSV-1 neutralizing antibody. Nonetheless, these mice were partially protected from lethal challenge with HSV-1 (75% survival). This protection was significant (P = 0.02). Despite some protection against death, gK-vaccinated mice showed no protection against the establishment of latency. Surprisingly, gK-vaccinated mice that were challenged ocularly with a stromal disease-producing strain of HSV-1 had significantly higher levels of ocular disease (herpes stromal keratitis) than did mock-vaccinated mice. In summary, this is the first report to show that vaccination with HSV-1 gK can provide protection against lethal HSV-1 challenge and that vaccination with an HSV-1 glycoprotein can significantly increase the severity of HSV-1-induced ocular disease.

The biology of the glomerulus: endothelial cells

Endothelial cells are active participants in processes controlling coagulation, inflammation and immune processes and an aberration in the controlling mechanisms may contribute to the development of disease within the glomerulus. The major goal of the next few years will be to develop reliable and reproducible methods for isolation and culture of glomerular endothelial cells so that their properties, and interactions with other glomerular cells, may be studied in vitro.

Passive hemagglutination assays for the detection of antibodies to herpes viruses

A simple and effective method for the detection of antibodies to herpes simplex virus (HSV), human cytomegalovirus (HCMV) and varicella-zoster virus (VZV), has been established using the passive hemagglutination assay (PHA) in combination with viral specific glycoproteins. The results obtained with the PHA were compared with those from neutralization (NT) and complement fixation (CF) tests. The PHA test for each of the herpes viruses appears to compare favorably with the other assays tested. The specificity and sensitivity of HSV PHA to NT were 100%, whereas the specificity and sensitivity of HSV CF test to NT were 98% and 100%, respectively. For HCMV, the specificity and sensitivity of PHA to NT and PHA to CF were 100%. Similarly, the specificity and sensitivity of VZV PHA to NT were 100%. Because of the low sensitivity of the VZV CF, the sensitivity of CF to NT was 83%. Furthermore, the range of antibody titers and their absolute levels obtained in the PHAs were significantly greater than those in the NT and CF tests.

FcR may function as a progression factor of nonlymphoid tumors

Tumor progression is a multistep process involving genetic and epigenetic changes in a transformed clone. Some of these changes may be induced by host factors which may also select for transformed cellular variants with a high ability to survive and propagate. In this article we review studies showing that receptors for the Fc portion of IgG may be expressed on cells from human or animal tumors of nonlymphoid origin. We also review data demonstrating that at least with respect to cells transformed in vitro with Polyoma virus, transformation per se is not sufficient for the induction of Fc receptor expression. We also summarize preliminary data showing that Fc receptor expression is causally involved in conferring a high malignancy phenotype upon transformed cells. Possible mechanisms to explain these observations are discussed.

Baculovirus-expressed glycoprotein G of herpes simplex virus type 1 partially protects vaccinated mice against lethal HSV-1 challenge

The DNA sequence encoding the complete HSV-1 glycoprotein G (gG) was inserted into a baculovirus transfer vector and recombinant viruses expressing gG were isolated. Three gG-related recombinant baculovirus expressed peptides of 37, 42, and 44 kDa were detected by Western blotting using monoclonal antibody to gG. The 42- and 44-kDa species were susceptible to tunicamycin, Endoglycosidase H (Endo-H), and N-glycosidase F (PNGase F) treatments, suggesting that they were glycosylated. Although only very low levels (approximately 1:10) of HSV-1-neutralizing antibody were produced in mice vaccinated with the baculovirus gG, these mice were partially protected from lethal challenge with HSV-1 (75-78% survival) and this level of protection was highly significant (P = 0.002). This is the first report to show that vaccination with HSV-1 gG can provide mice with any level of protection against lethal HSV-1 challenge.

Receptor properties of two varicella-zoster virus glycoproteins, gpI and gpIV, homologous to herpes simplex virus gE and gI

The varicella-zoster virus (VZV) genome contains 70 reading frames (ORF), 5 of which encode the glycoproteins gpI, gpII, gpIII, gpIV, and gpV. ORF 67 and 68 lie adjacent to each other in the unique short region of the VZV genome and code for gpIV and gpI, respectively. These two genes, which are contained within the HindIII C fragment of the VZV genome, were subcloned in the correct orientation downstream from the promoter regions of the eukaryotic expression vectors pCMV5 and pBJ. After transfection, 5 to 20% of the Cos cells bound antibody specific for the given glycoprotein. In this study, it was shown that only the cells transfected with the gpI construct bound to the Fc fragment of human immunoglobulin G. Neither the transfected gpIV gene product nor the vector only bound to the Fc fragment. Thus, VZV gpI is confirmed to be the VZV-encoded Fc-binding glycoprotein. Like the wild-type form of gpI expressed in VZV-infected cells, gpI precipitated from transfected cells contained both N-linked and O-linked glycans and was heavily sialated. In addition, the transfected gpI gene product was phosphorylated both in cell culture and in protein kinase assays by mammalian casein kinases I and II. Extensive computer-assisted analyses of the VZV gpI sequence, as well as those of alphaherpesviral homolog glycoproteins, disclosed properties similar to those of other cell surface receptors; these included (i) exocytoplasmic regions rich in cysteine residues, (ii) membrane-proximal regions with potential O-linked glycosylation sites, and (iii) cytoplasmic domains with consensus phosphorylation sites.

Baculovirus-expressed glycoprotein E (gE) of herpes simplex virus type-1 (HSV-1) protects mice against lethal intraperitoneal and lethal ocular HSV-1 challenge

We have constructed a recombinant baculovirus expressing high levels of the herpes simplex virus type 1 (HSV-1) glycoprotein E (gE) in Sf9 cells. The expressed gE migrated on gels as a double band with apparent molecular weights of 68 and 70 kDa. The recombinant gE was glycosylated based on its susceptibility to tunicamycin treatment and was transported to the membrane of Sf9 cells based on indirect immunofluorescence. Mice vaccinated with gE developed high serum titers of HSV-1-neutralizing antibodies based on plaque reduction assays. gE vaccination also induced a strong delayed type hypersensitivity (DTH) response to HSV-1. In addition, mice vaccinated with the recombinant gE were protected from both intraperitoneal and ocular lethal HSV-1 challenge. To our knowledge, this is the first report in which vaccination with gE was shown to induce high neutralizing antibody titers, a DTH response, or protection against lethal HSV-1 challenge.

Expression of herpes simplex virus type 1 glycoprotein I in baculovirus: preliminary biochemical characterization and protection studies

We have constructed a recombinant baculovirus expressing the herpes simplex virus type 1 (HSV-1) glycoprotein I (gI). Sf9 cells infected with this recombinant virus synthesized gI-related polypeptides with apparent molecular sizes of 52 and 56 kDa. The recombinant gI appeared to be glycosylated, since it was susceptible to both tunicamycin and endoglycosidase H, and the expressed gI was transported to the surface of infected cells as judged by indirect immunofluorescence. Antibodies to the recombinant gI raised in mice neutralized HSV-1 infectivity. Finally, we show here for the first time that vaccination with gI can protect mice against HSV-1 challenge.

Warner-Lambert/Parke-Davis Award Lecture. Viral pathogenesis of atherosclerosis. Impact of molecular mimicry and viral genes

Human atherogenesis is a pleiotropic process with an undefined cause. Several pathologic factors have been linked to the disease process, including arterial injury or activation of the endothelium, which may injury or activation of the endothelium, which may initiate proatherosclerotic events in the vessel wall. Atherosclerotic lesions are characterized, in part, by the presence of activated immune cells, abnormal cell proliferation, and altered cholesterol metabolism. These activated immunocompetent cells in plaques produce vasoactive mediators that can alter homeostasis and may promote the arteriopathy. Both molecular and structural evidence is presented that herpesviruses, by way of induction of altered gene function and cellular cholesterol metabolism, coupled with their ability to activate coagulation and a monocyte receptor on the infected endothelium, are involved in major pathogenic events associated with atherosclerosis and thrombosis. Work from the author's laboratory, as well as from other research groups, have shown that avian and human herpesviruses act specifically to induce alterations to the surface and inner layers of the blood vessel wall that may predispose to atherosclerosis and its attendant clinical complications.

Identification of a monocyte receptor on herpesvirus-infected endothelial cells

The adhesion of circulating blood cells to vascular endothelium may be an initial step in atherosclerosis, inflammation, and wound healing. One mechanism for promoting cell-cell adhesion involves the expression of adhesion molecules on the surface of the target cell. Herpes simplex virus infection of endothelium induces arterial injury and has been implicated in the development of human atherosclerosis. We now demonstrate that HSV-infected endothelial cells express the adhesion molecule GMP140 and that this requires cell surface expression of HSV glycoprotein C and local thrombin generation. Monocyte adhesion to HSV-infected endothelial cells was completely inhibited by anti-GMP140 antibodies but not by antibodies to other adhesion molecules such as VCAM and ELAM-1. The induction of GMP140 expression on HSV-infected endothelium may be an important pathophysiological mechanism in virus-induced cell injury and inflammation.

The effect of virus infection on the adherence of leukocytes or platelets to endothelial cells

It has been reported that atherosclerotic lesions contain genomic material belonging to members of the herpes family. This suggests that latent viral infection may be one of the atherogenic triggers. In this study we show that early infection of endothelial cell monolayers with Herpes Simplex virus type 1 (HSV-1) or Cytomegalovirus (CMV) results in an increased monocyte (MC) and polymorphonuclear leukocyte (PMN) adherence, but not in an increased platelet adhesion. Further, is demonstrated that MC and PMN respond differently to virus infected endothelial cell monolayers: PMN adhesion to CMV infected cells is approximately 430% of the control adherence, while the MC adherence is increased to 160%. Also, a difference in virus acting is observed: the adherence of MC or PMN to HSV-1 infected endothelial cells is caused by a secreted adherence promoting factor, while the adherence of MC or PMN to CMV infected endothelial cells seems to be a cell-bound phenomenon. In addition, it was demonstrated that the augmentation of MC or PMN adherence to virus infected endothelial cells is sensitive to tunicamycin, suggesting that both virus infections induce the expression of glycoproteins on the endothelial cell membrane, which is responsible for the MC and PMN adhesion. Thus, HSV-1 and CMV infection of endothelium results in an increased adherence of leukocytes which is suggested, irrespective of the precise nature of the mechanism of virus induced atherosclerosis, to be the earliest event associated with endothelium cell damage.

Effect of interferon treatment on expression of gC and gE glycoproteins in herpes simplex virus-infected cells

The effect of interferon treatment on the herpes simplex virus type 1 (HSV-1)-specific glycoproteins gC and gE in homologous and heterologous cells has been investigated. In human embryonic fibroblastic cells, human leukocyte interferon inhibited virus multiplication and expression of the HSV-1-specific glycoproteins gC and gE on the cell surface in a dose-dependent manner. In heterologous baby hamster kidney cells, the human interferon had no effect on virus multiplication. However, the surface expression of the HSV-1-specific glycoproteins was reduced, as shown by erythrocyte rosette formation, by attachment of monodisperse polystyrene particles coated with antibodies and by immunogold scanning electron microscopy.

Cytomegalovirus induced PMN adherence in relation to an ELAM-1 antigen present on infected endothelial cell monolayers

In human umbilical vein endothelial cells infected with cytomegalovirus (CMV), an activation antigen recognized by monoclonal antibody (mAb) ENA1 appeared. mAb ENA1 reacts with an inducible endothelial surface antigen which has characteristics similar to those of ELAM-1. Incubation with anti-IL-1 partly inhibited this appearance and, parallel to this, the virus-induced polymorphonuclear cell (PMN) adhesion was decreased. In addition, the adhesion of PMN to virus-infected endothelial cells could be reduced by F(ab)2 fragments of mAb ENA1 to almost control level. The results obtained after incubation of PMN with mAb IB4 (against CD18) suggest that the adhesion of PMN to uninfected endothelial cells is CD18 glycoprotein dependent, and virus infection up-regulates this glycoprotein-dependent mechanism. These results indicate that the virus-induced PMN adhesion is regulated by the following mechanism: virus infection of endothelial cells induces IL-1 production, and the autocrine IL-1 causes the expression of ELAM-1 on the surface of endothelial cells. In turn this activation antigen ELAM-1 binds with its putative ligand present on the PMN membrane. The virus-induced PMN adhesion occurs also through a CD18 glycoprotein-dependent mechanism.

Cell surface expression of the varicella-zoster virus glycoproteins and Fc receptor

Varicella-zoster virus (VZV) specifies the synthesis of viral glycoproteins which are important antigens for induction of the host immune response. In this report the technology of laser-activated flow cytometry has been employed to measure the membrane expression of VZV glycoproteins gpI, gpII, gpIII, and gpIV. By use of biotinylated monoclonal antibodies as probes, all four glycoproteins were demonstrated on the infected cell surface. The temporal appearance of the viral glycoproteins was defined in a time course experiment and shown to be maximal about 24 hr postinfection. The issue whether VZV induces the cell surface expression of an Fc receptor (FcR) was investigated with biotinylated nonimmune human IgG, followed by streptavidin-phycoerythrin. By this technique a 10-fold increase in fluorescence intensity was seen in the VZV-infected cells as compared to the mock-infected controls. When the experiment was repeated with purified human Fc fragment rather than whole IgG, a similar degree of binding was seen. Both the VZV glycoproteins and the VZV FcR were exquisitely sensitive to trypsin treatment (1 mg/ml); likewise, the cell surface expression of these VZV products was diminished by treatment of the infected cultures with monensin, an inhibitor of glycoprotein transport. In order to prove that VZV infection was not causing the induction of a cellular Fc gamma R, the VZV-infected and mock-infected cells were stained with monoclonal antibodies directed against each of the three human cellular IgG FcR, but no differences were observed. Therefore, the FcR activity seen in the infected culture was not due to one of the known cellular Fc gamma R.

Immunogenicity of herpes simplex virus type 1 glycoproteins expressed in vaccinia virus recombinants

Vaccinia virus recombinants expressing glycoproteins B (vgB11), D (VgD52), E (gE/7.5 and gE/4B), G (gG-vac), H (gH-vac), and I (gI-vac) of HSV-1 were used to compare the protective response to these individual glycoproteins in the mouse. Glycoprotein D induced the best neutralizing antibody titers and the most increased rates of HSV clearance from the ear as well as good protection from the establishment of latent HSV infections in the sensory ganglia. Glycoprotein B also induced good neutralizing antibody titers and as great a protection from the establishment of latency as gD although the rate of virus clearance from the ear was not as great as after immunization with gD. Glycoprotein E induced weak neutralizing antibody but gG, gH, and gI did not show a neutralizing antibody response. At higher challenge doses of virus (10(6) PFU HSV-1 in the ear), gE induced a protective response by increasing the rate of virus clearance and reducing the acute infection of ganglia as compared to negative control immunized mice. However there was no protection from the establishment of latent infections after immunization with gE. No protective response was seen to gG, gH, or gl.

Herpes simplex virus type 1 encodes two Fc receptors which have different binding characteristics for monomeric immunoglobulin G (IgG) and IgG complexes

Two herpes simplex virus type 1 glycoproteins, gE and gI, have been shown to form a complex that binds the Fc domain of immunoglobulin G (IgG). We demonstrate that this complex is required for the binding of monomeric nonimmune IgG but that gE alone is sufficient for binding polymeric IgG in the form of IgG complexes. Evidence that gE but not gI is required for binding IgG complexes is as follows. IgG complexes bound equally well to cells infected with gI-negative mutants or with wild-type virus, whereas cells infected with gE-negative mutants did not bind IgG complexes. Furthermore, L cells transiently transfected to express gE bound IgG complexes. Additional evidence that gI fails to augment binding of IgG complexes comes from experiments in which the gI gene was inducibly expressed in cells after infection. Inducible gI expression failed to increase binding of IgG complexes to infected cells in comparison with cells not capable of inducible gI expression. In contrast, expression of both gE and gI was necessary for binding of monomeric IgG, as demonstrated by flow cytometry using cells infected with gE-negative and gI-negative mutants. These observations demonstrate that herpes simplex virus type 1 Fc receptors (FcRs) have different binding characteristics for monomeric IgG and IgG complexes. Furthermore, it appears that gE is the FcR for IgG complexes and that gE and gI form the FcR for monomeric IgG.

Viral activation of the coagulation cascade: molecular interactions at the surface of infected endothelial cells

Herpesviral infection of endothelial cells (ECs) induces arterial injury. We now demonstrate that such infection promoted enhanced monocyte-endothelial adhesion. Enhanced adhesion was blocked by monoclonal antibodies to the viral-encoded cell surface glycoprotein gC but not by antibodies to gD or gE. Adhesion was also blocked by treating ECs with specific thrombin inhibitors or by growing cells in prothrombin-depleted serum. We found that gC bound and promoted activation of factor X on infected ECs, thereby contributing to thrombin generation. Factor X also bound to transfected L cells that were induced to express gC. Cross-linking and immunoprecipitation studies demonstrated factor X-gC complex formation on the surface of these cells. We suggest that gC-dependent thrombin generation by herpes-infected endothelium may be an important mediator of vascular pathology during viral infection.

Induction of immunoglobulin G Fc receptors by recombinant vaccinia viruses expressing glycoproteins E and I of herpes simplex virus type 1

Glycoprotein E (gE) of herpes simplex virus type 1 (HSV-1) will bind immunoglobulin G (IgG) (Fc) affinity columns (R. B. Bauke and P. G. Spear, J. Virol. 32:779-789, 1979), but recent evidence suggests that the HSV-1 Fc receptor is composed of a complex of gE and glycoprotein I (gI) and that both gI and gE are required for Fc receptor activity (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987; D. C. Johnson, M. C. Frame, M. W. Ligas, A. M. Cross, and N. D. Stow, J. Virol. 62:1347-1354, 1988). We have expressed gE and gI, either alone or in combination, on the surface of HeLa cells by using recombinant vaccinia viruses and have measured Fc receptor activity by Fc-rosetting or IgG-binding assays. Expression of gE alone resulted in the induction of Fc receptor activity, while expression of gI alone gave no detectable Fc binding. Coexpression of gE and gI resulted in higher levels of IgG binding than did expression of gE alone, despite the fact that under conditions of coexpression, the levels of surface gE were reduced. We propose that gE and gI together form a receptor of higher affinity than gE alone and that HSV-1 therefore has the potential to induce two Fc receptors of different affinities.

Conserved epitopes of simian herpesvirus SA 8 and bovine herpesvirus type 2

Some major structural components of simian herpesvirus SA 8 were analyzed and the relationship of SA 8 with HSV-1 and especially with BHV-2 was further characterized using a panel of SA 8- and BHV-2-specific monoclonal antibodies directed against gB, gD, gE, and ICP 8. It could be shown that SA 8 and BHV-2 expressed gB-1 equivalents, which differ in electrophoretic mobility, but share common epitopes with HSV-1. The antigenic determinants were detectable in the cytoplasm, on the surface of infected cells and on the virus envelope. Monoclonal antibodies reactive with epitopes of gB-SA 8 and gB-BHV-2 neutralized the homologous virus and cross-neutralized only HSV-1 and HSV-2, suggesting differences in accessibility of the corresponding epitope on SA 8 and BHV-2, respectively. A second protein with conserved epitopes on SA 8, BHV-2, and HSV-1 was identified as ICP 8. This nucleus associated protein was additionally detected on the envelope of SA 8 and HSV-1. The results imply that ICP 8 might have a function not only in virus replication, but also in virus assembly. We could furthermore define type-specific epitopes on two SA 8 envelope proteins which are analogous to gD-1 and gE-1, respectively. The gD-specific epitope induced a type-specific neutralizing antibody, making it interesting for differentiation of closely related herpesviruses.

A novel function of the herpes simplex virus type 1 Fc receptor: participation in bipolar bridging of antiviral immunoglobulin G

We describe a novel function of the Fc receptor of herpes simplex virus type 1 (HSV-1), its ability to participate in antibody bipolar bridging. This refers to the binding of a single immunoglobulin G (IgG) molecule by its Fab end to its antigenic target and by its Fc end to an Fc receptor (FcR). We demonstrate that various immune IgG antibodies, including polyclonal rabbit antibodies to HSV-1 glycoproteins gC1 and gD1 and monoclonal human antibody to gD1 blocked rosetting of IgG-coated erythrocytes at IgG concentrations 100- to 2,000-fold lower than required for rosette inhibition with nonimmune IgG. Steric hindrance did not account for the observed differences between immune and nonimmune IgG since rabbit anti-gC1 F(ab')2 fragments did not block rosetting. Murine anti-gC1 or anti-gD1 IgG, a species of IgG incapable of binding by its Fc end to the HSV-1 FcR, also did not block rosetting. When cells were infected with a gC1-deficient mutant, anti-gC1 IgG inhibited rosetting to the same extent as nonimmune IgG. This indicates that binding by the Fab end of the IgG molecule was required for maximum inhibition of rosetting. Bipolar bridging was shown to occur even when small concentrations of immune IgG were present in physiologic concentrations of nonimmune IgG. The biologic relevance of antibody bipolar bridging was evaluated by comparing antibody- and complement-dependent virus neutralization of an FcR-negative mutant and its parent HSV-1 strain. By engaging the Fc end of antiviral IgG, the parent strain resisted neutralization mediated by the classical complement pathway. These observations provide insight into the role of the HSV-1 FcR in pathogenesis and may help explain the function of FcR detected on other microorganisms.

Relatedness of glycoproteins expressed on the surface of simian herpes-virus virions and infected cells to specific HSV glycoproteins

The antigenic relatedness of the surface glycoprotein antigens of six herpesviruses indigenous to human and nonhuman primates was examined. Binding of anti-viral sera to viral antigens expressed on the surface of infected cells demonstrated that the surface antigens of herpes simplex virus type 1 (HSV 1), HSV 2, simian agent 8 (SA8), and Herpesvirus simiae (B virus) exhibit extensive cross-reactivity. Surface antigens of two viruses isolated from South American primates, H. saimiri 1 (HVS 1) and H. ateles 1 (HVA 1), were comparatively more virus-specific in their antigenic reactivity. Endpoint neutralization tests performed in the presence and absence of complement confirmed these results. Immunoprecipitation of viral proteins was used to identify those representing cross-reactive surface antigens. A glycoprotein of approximately 110,000-125,000 Daltons (110-125 k) was immunoprecipitated from cells infected with each of the six primate herpesvirus by antisera to each of the viruses. Using monospecific antisera, these glycoproteins were shown to be antigenically related to the gB glycoproteins of HSV. Although these glycoproteins were antigenically conserved among all six viruses, antibodies to the gB glycoproteins did not cross-neutralize heterologous viruses. A glycoprotein of approximately 60-70 k was precipitated from HSV 1, HSV 2, SA8, and B virus infected cells by antisera to each of these four viruses. These SA8 and B virus glycoproteins were shown to be antigenically related to the gD glycoproteins of HSV 1 and HSV 2 and to be involved in cross-neutralization among these viruses. Antisera to HVS 1 and HVA 1 did not recognize these gD glycoproteins nor was a glycoprotein of similar molecular weight precipitable from HVS 1 or HVA 1 infected cells by antisera to the other four viruses. Southern blot hybridizations using probes for HSV glycoprotein genes confirmed the conservation of the gB glycoproteins among all the simian viruses and of the gD gene in SA8 and B virus. A glycoprotein of approximately 75-80 k was, however, precipitated from HVS 1 and HVA 1 infected cells by antisera to either of these two viruses. In addition, at least one glycoprotein which appeared to be predominantly virus-specific in its reactivity was identified for five of the viruses.

Virus induced adherence of monocytes to endothelial cells

In this study we have demonstrated that infection of human umbilical vein endothelial cells (HUVEC) with Herpes simplex virus type 1 (HSV-1) resulted in an increased adherence of monocytes (MC). This enhanced adherence occurred at 3 h post infection (p.i.) when about 20% of the monolayer is infected and when there is no cytopathic effect observable in the monolayer. The adherence of human MC to virus-infected HUVEC monolayers proved to be effective and reproducible if a multiplicity of infection (MOI) of ten and a ratio of number of MC to number of HUVEC of 5 was used. The increased adherence was also induced by incubating non-infected HUVEC with the 'supernatant medium' of the HSV-1 infected cells, showing that soluble factors induced by viral infection are responsible for the increased adherence. The augmentation of MC adherence to infected endothelium was sensitive to tunicamycin treatment, suggesting that the MC adherence is probably mediated by glycoproteins expressed on the HUVEC membranes by virus infection.

Fc receptors in corneal epithelium

The corneal epithelia of the mouse, rabbit and human were shown to contain Fc receptors by an indirect method with immunoglobulins, labelled second antibody and the avidin-biotin peroxidase complex (ABC); and a direct method with the peroxidase conjugated Fc fragment. The cornea epithelia of all three species exhibited a high concentration of the Fc gamma R with either homologous or heterologous immunoglobulins. The binding specificity of Fc receptors was further supported by competitive inhibition of binding of labeled antibody by homologous, unlabeled antibody. Although Fc alpha R was also present it was at a much lower concentration. The Fc receptor for IgM (Fc microR) was difficult to demonstrate. However, it appeared to be present in very low concentration on only the mouse and rabbit corneal epithelium.

Neutralizing activity of antibodies against the major herpes simplex virus type 1 glycoproteins

The specificity and neutralizing activity of antibodies against the major herpes simplex virus type 1 (HSV-1) glycoproteins were tested in serum samples of patients with a history of HSV-1 infection. By preabsorption of sera to preparations of native and denatured HSV-1 proteins, followed by immunoblotting and microneutralization, it was shown that the majority of neutralizing antibodies are directed against denaturation-sensitive epitopes. Furthermore, preabsorption of sera to proteins of viral ts and deletion mutants revealed that antibodies specific for gB, gC, and gE had a low neutralizing activity. These results suggest a major role of anti-gD in neutralization of viral infectivity. In addition, it was shown that antibodies directed against the gB monomer were distinct from antibodies against the gB homodimers. The latter, however, did not reveal any measurable neutralizing activity.

Complex between glycoproteins gI and gp63 of pseudorabies virus: its effect on virus replication

To ascertain the biological functions of different glycoproteins that are nonessential for pseudorabies virus growth in vitro, we have constructed mutants defective in one (or a combination) of these glycoproteins and have examined various aspects of their role in the infective process. We made the following two observations. (i) Glycoproteins gI and gp63 are noncovalently complexed to each other. They are coprecipitated by antisera against either one of these glycoproteins but do not share antigenic determinants: monoclonal antibodies against gp63 do not immunoprecipitate gI from extracts of gp63- mutant-infected cells, and monoclonal antibodies against gI do not immunoprecipitate gp63 from extracts of gI- mutant-infected cells. (ii) Mutants unable to synthesize either gI or gp63 have some common biological characteristics; they have a growth advantage in primary chicken embryo fibroblasts. Furthermore, we have shown previously that in conjunction with glycoprotein gIII, gI and gp63 are necessary for the expression of virulence (T. C. Mettenleiter, C. Schreurs, F. Zuckermann, T. Ben-Porat, and A. S. Kaplan, J. Virol. 62, 2712-2717, 1988). These results show that the functional entity affecting virus replication in chicken embryo fibroblasts, as well as affecting virulence, is the complex between gI and gp63. The gI-gp63 complex of pseudorabies virus does not appear to have Fc receptor activity as does its homolog, the gI-gE complex of herpes simplex virus.

Pathogenicity of glycoprotein C negative mutants of herpes simplex virus type 1 for the mouse central nervous system

A previous study from our laboratory showed that a mutant of herpes simplex virus type 1 (HSV-1), strain KOS-321, carrying a deletion in the structural gene for glycoprotein C (gC) had reduced pathogenicity for the mouse central nervous system when compared to the wild-type virus (Kümel et al., 1985). In this study, eight additional gC negative (gC-) mutants derived from KOS-321 were shown to vary widely in their ability to induce lethal encephalitis in female DBA/2 mice following intracerebral inoculation. This variation in virulence showed no correlation with thymidine kinase activity. One less virulent gC- strain, gC-39, was further studied to determine whether the neurovirulent phenotype could be restored by rescue of the gC gene using standard marker rescue cotransfection procedures. The resulting progeny contained 2% gC+ recombinant virions and was tested for its ability to cause encephalitis. Although this progeny had increased virulence, it was not attributable to the acquisition of the gC gene since passive immunization of mice with a pool of anti-gC monoclonal antibodies had no effect on the development of encephalitis and only gC- viruses were isolated from diseased brain tissues. In agreement with these findings, individual plaque-purified gC positive (gC+) virus recombinants were shown not to have been restored to the wild-type virus level of neurovirulence. It is concluded that gC is not a virulence determinant in this mouse model of HSV-induced encephalitis and that cotransfection procedures can induce additional mutations that affect viral pathogenesis.

Herpes simplex virus immunoglobulin G Fc receptor activity depends on a complex of two viral glycoproteins, gE and gI

Evidence was recently presented that herpes simplex virus type 1 (HSV-1) immunoglobulin G (IgG) Fc receptors are composed of a complex containing a previously described glycoprotein, gE, and a novel virus-induced polypeptide, provisionally named g70 (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987). Using a monoclonal antibody designated 3104, which recognizes g70, in conjunction with antipeptide sera and virus mutants unable to express g70 or gE, we have mapped the gene encoding g70 to the US7 open reading frame of HSV-1 adjacent to the gE gene. Therefore, g70 appears to be identical to a recently described polypeptide which was named gI (R. Longnecker, S. Chatterjee, R. J. Whitley, and B. Roizman, Proc. Natl. Acad. Sci. USA 84:147-151, 1987). Under mildly denaturing conditions, monoclonal antibody 3104 precipitated both gI and gE from extracts of HSV-1-infected cells. In addition, rabbit IgG precipitated the gE-gI complex from extracts of cells transfected with a fragment of HSV-1 DNA containing the gI, gE, and US9 genes. Cells infected with mutant viruses which were unable to express gE or gI did not bind radiolabeled IgG; however, cells coinfected with two viruses, one unable to express gE and the other unable to express gI, bound levels of IgG approaching those observed with wild-type viruses. These results further support the hypothesis that gE and gI form a complex which binds IgG by the Fc domain and that neither polypeptide alone can bind IgG.

Complement component C3b binds directly to purified glycoprotein C of herpes simplex virus types 1 and 2

Cells infected with herpes simplex virus type 1 (HSV-1), but not HSV-2, express on their surfaces a receptor for the complement component C3b. Receptor activity is markedly enhanced by treatment of the infected cells with neuraminidase. Employing a direct binding assay, consisting of purified HSV glycoproteins immobilized on nitrocellulose and iodinated C3b as a probe, we found that C3b binds directly to gC-1, as well as to gC-2, but not to gB or gD from either serotype. C3b binding was enhanced by treatment of gC-1 or gC-2 with neuraminidase. Endo F or endo H treatment of gC-1 had no effect on C3b binding. However, treatment of gC-2 with these endoglycosidases had a marked negative effect on C3b binding. These results suggest that N-linked oligosaccharides are involved in binding of C3b to gC-2, but not gC-1. Alternatively, removal of N-linked oligosaccharides from gC-2 might adversely affect polypeptide conformation. Glycoprotein C-2 also differs from gC-1 in its effects on the complement cascade. Whereas gC-1 accelerated the decay of the alternative pathway C3 convertase and impaired the efficiency of lysis by the components C5 through C9, gC-2 stabilized the active C3 convertase and had little effect on the late-acting components. The dissimilarity of gC-1 and gC-2 with regard to their effects on the complement cascade may have implications regarding the role of these glycoproteins in confronting the host immune response.

Potentiated adherence of sickle erythrocytes to endothelium infected by virus

Systemic viral infection is a known precipitant of vasocclusive crisis in sickle patients, but the mechanism underlying this clinical observation is unknown. In the present studies, human umbilical vein endothelial cells were infected with Herpes simplex virus type 1 (HSV) to model systemic viral disease. The already abnormal adherence of sickle erythrocytes to control endothelium is enhanced 1.8 +/- 0.4-fold to HSV-infected endothelium (P less than 0.001). This component of potentiated adherence is eliminated by maneuvers that block Fc receptors, it is prevented by tunicamycin, and it is not seen using a mutant HSV that is unable to express the Fc receptor glycoprotein. Thus, the incremental adherence seen here occurs due to expression of Fc receptor activity on HSV-infected endothelium and the consequent recognition of abnormal amounts of IgG on sickle erythrocytes. We conclude that systemic viral infection potentially can induce a novel mechanism for enhancement of erythrocyte adherence to endothelium and that this may increase the likelihood of vasocclusion during viral infection.

Cells expressing herpes simplex virus glycoprotein gC but not gB, gD, or gE are recognized by murine virus-specific cytotoxic T lymphocytes

To determine which viral molecule(s) is recognized by herpes simplex virus (HSV)-specific cytotoxic T lymphocytes (CTL), target cells were constructed which express individual HSV glycoproteins. A mouse L cell line, Z4/6, which constitutively expressed high levels of HSV type 2 (HSV-2) gD (gD-2) was isolated and characterized previously (D. C. Johnson and J. R. Smiley, J. Virol. 54:682-689, 1985). Despite the expression of gD on the surface of Z4/6 cells, these cells were not killed by anti-HSV-2 CTL generated following intravaginal infection of syngeneic mice. In contrast, parental Z4 or Z4/6 cells infected with HSV-2 were lysed. Furthermore, unlabeled Z4/6 cells were unable to block the lysis of HSV-2-infected labeled target cells. Cells which express HSV-1 gB (gB-1) were isolated by transfecting L cells with the recombinant plasmid pSV2gBneo, which contains the HSV-1 gB structural sequences and the neomycin resistance gene coupled to the simian virus 40 early promoter and selecting G418-resistant cell lines. One such cell line, Lta/gB15, expressed gB which was detected by immunoprecipitation and at the cell surface by immunofluorescence. Additionally, cells expressing HSV-1 gC (gC-1) or gE (gE-1) were isolated by transfecting Z4 cells, which are L cells expressing ICP4 and ICP47, with either the recombinant plasmid pGE15neo, which contains the gE structural sequences and the neomycin resistance gene, or pDC17, which contains the gC structural gene coupled to the gD-1 promoter. A number of G418-resistant cell lines were isolated which expressed gC-1 or gE-1 at the cell surface. Anti-HSV-1 CTL generated following footpad infection of syngeneic mice were unable to lyse target cells expressing gB-1 or gE-1. In contrast, target cells expressing very low levels of gC-1 were killed as well as HSV-1-infected target cells. Furthermore, infection of gC-1-transformed target cells with wild-type HSV-1 or a strain of HSV-1 that does not express gC did not result in a marked increase in susceptibility to lysis. These results suggest that murine class I major histocompatibility complex-restricted anti-HSV CTL recognize gC-1 but do not recognize gB, gD, or gE as these molecules are expressed in transfected syngeneic target cells. The results are discussed in terms of recent evidence concerning the specificity of antiviral CTL.

Identification of a novel herpes simplex virus type 1-induced glycoprotein which complexes with gE and binds immunoglobulin

We detected a glycoprotein on the surface of cells infected with herpes simplex virus type 1 (HSV-1) which, in conjunction with gE, binds immunoglobulin G (IgG). The novel glycoprotein, which has an apparent molecular mass of 70 kilodaltons and was provisionally named g70, was first detected in extracts of HSV-1-infected cells labeled by lactoperoxidase-catalyzed iodination and precipitated with rabbit sera or IgG and protein A-Sepharose. In subsequent experiments, g70 and gE were coprecipitated from extracts of HSV-1-infected cells labeled with [35S]methionine, [35S]cysteine, or 14C-amino acids. We were unable to precipitate a polypeptide analogous to g70 or gE from extracts of HSV-2-infected cells with rabbit IgG and protein A-Sepharose. Partial proteolytic peptide analysis indicated that g70 is structurally distinct from gE and gI). In addition, g70 was electrophoretically distinct from the HSV-1 Us4 glycoprotein gG. HSV-1 gE, expressed in mouse cells transfected with the gE gene, was not precipitated with rabbit IgG, nor could these cells bind radiolabeled IgG, suggesting that gE alone cannot act as an IgG (Fc) receptor. This result, coupled with the findings that gE and g70 are coprecipitated with IgG and with an anti-gE monoclonal antibody, suggests that gE and g70 form a complex which binds IgG. The electrophoretic mobilities of g70 molecules induced by different strains of HSV-1 differed markedly, arguing that g70 is encoded by the virus and is not a cellular protein induced by virus infection.