Immunoglobulin G(Fc)-binding receptors on virions of herpes simplex virus type 1 and transfer of these receptors to the cell surface by infection

Development of a microneutralization assay for HSV-2

BACKGROUND

Plaque Reduction Neutralization Test (PRNT) is the standard assay used for measuring neutralizing antibody responses to Herpes simplex virus type-2 (HSV-2). The PRNT is a cumbersome, time-consuming and laborious assay. The development of a faster, high throughput microneutralization assay (MNA) for HSV-2 viruses carried out in a 96-well format will allow for rapid testing of large numbers of samples for drug and vaccine development.

METHODS

We describe the generation of a MNA that utilizes a pair of anti-HSV human monoclonal antibodies (mAbs) for virus detection in HSV-2 infected Vero cells. Antibodies were generated by B-cell cloning from PBMC's isolated from HSV-1 negative/HSV-2 positive donors. We describe the selection and characterization of the antibodies used for virus detection by ELISA with purified, recombinant anti-HSV glycoproteins, antibody binding in infected cells, and Western Blot. We determine the anti-HSV-2 neutralizing titers of immune sera from mice by MNA and PRNT and compare these results by linear regression analysis.

RESULTS

We show that neutralization titers for HSV-2, determined by the 96-well MNA correlate with titers determined by a PRNT completed in 24-well plates in both the absence (R² = 0.8250) and presence (R² = 0.7075) of complement.

CONCLUSIONS

We have successfully developed an MNA that can be used in place of the burdensome PRNT to determine anti-HSV-2 neutralizing activity in serum. This MNA has much greater throughput than the PRNT, allowing many more samples to be processed in a shorter time saving ∼90 % of the time required by the laboratory scientist to complete the task as compared to the traditional PRNT.

HSV-1-Specific IgG Subclasses Distribution and Serum Neutralizing Activity in Alzheimer's Disease and in Mild Cognitive Impairment

Human Herpes Simplex Virus type 1 (HSV-1) infection is suggested to play a role in the development of Alzheimer's disease (AD). Immunoglobulin G (IgG) neutralize HSV-1 activity, but the virus can evade IgG-mediated immune responses by expressing receptor that efficiently binds the Fc portion of all IgG subclasses with the exception of IgG3. We analyzed HSV-1-specific IgG subclasses and IgG-mediated serum neutralization activity against HSV-1 in individuals with a diagnosis of either AD or mild cognitive impairment (MCI), comparing the results with those obtained in age-matched healthy controls (HC). 186 individuals were enrolled in the study: 67 AD, 58 MCI, and 61 HC. HSV-1 IgG titers and subclasses, neutralizing antibody (NAb) titers, and complement C3 concentration-critical component of antibody-mediated effector activity-were measured in sera by ELISA; IgG neutralizing activity was performed on HSV-1 infected Vero cells. Results showed that, whereas HSV-1-specific IgG1, IgG2, and IgG4 titers as well as complement C3 serum concentration were comparable in all groups of individuals, IgG3 were more frequently detected in MCI (89%) compared to AD (75%; p < 0.05) and HC (68%; p = 0.003), whereas the titer is similar among the three groups (AD: 0.66±0.21 OD; MCI: 0.68±0.24 OD; HC: 0.72±0.28 OD). Notably, HSV-1 specific neutralizing ability of AD sera was reduced even in the presence of high quantity of IgG3. As IgG3 plays a key role in counteracting the ability of HSV-1 to evade immune responses, these data reinforce the hypothesis of a pathogenetic role of HSV-1 in AD.

Enrichment of high affinity subclasses and glycoforms from serum-derived IgG using FcγRs as affinity ligands

As antibodies continue to gain predominance in drug discovery and development pipelines, efforts to control and optimize their activity in vivo have matured to incorporate sophisticated abilities to manipulate engagement of specific Fc binding partners. Such efforts to promote diverse functional outcomes include modulating IgG-Fc affinity for FcγRs to alternatively potentiate or reduce effector functions, such as antibody-dependent cellular cytotoxicity and phagocytosis. While a number of natural and engineered Fc features capable of eliciting variable effector functions have been demonstrated in vitro and in vivo, elucidation of these important functional relationships has taken significant effort through use of diverse genetic, cellular and enzymatic techniques. As an orthogonal approach, we demonstrate use of FcγR as chromatographic affinity ligands to enrich and therefore simultaneously identify favored binding species from a complex mixture of serum-derived pooled polycloncal human IgG, a load material that contains the natural repertoire of Fc variants and post-translational modifications. The FcγR-enriched IgG was characterized for subclass and glycoform composition and the impact of this bioseparation step on antibody activity was measured in cell-based effector function assays including Natural Killer cell activation and monocyte phagocytosis. This work demonstrates a tractable means to rapidly distinguish complex functional relationships between two or more interacting biological agents by leveraging affinity chromatography followed by secondary analysis with high-resolution biophysical and functional assays and emphasizes a platform capable of surveying diverse natural post-translational modifications that may not be easily produced with high purity or easily accessible with recombinant expression techniques.

Varicella-zoster virus (VZV) and alpha 1 antitrypsin: a fatal outcome in a patient affected by endemic pemphigus foliaceus

BACKGROUND

Herpes virus infections are well known infectious complications of pemphigus and bullous pemphigoid. We describe pathologic findings utilizing autopsy tissue from several organs from a patient affected by a new variant of endemic pemphigus in El Bagre, Colombia, South America.

CASE REPORT

We describe a patient by a new variant of endemic pemphigus foliaceus from El Bagre that was receiving high-dosage immunosuppressants when hospitalized and died suddenly following contact with a second patient affected by chicken pox.

MATERIALS AND METHODS

We performed studies utilizing hematoxylin and eosin, immunohistochemistry, and direct immunofluorescence techniques on tissues from several organs.

RESULTS

We detected the presence of varicella zoster virus, as well as strong positivity for α-1 antitrypsin in the heart, kidneys, spleen, liver, skin, brain, lungs, pancreas, small and large intestines, and skeletal muscle. In regard to structural damage in the kidney and heart, we believe the observed damage is associated with the presence of autoantibodies to these organs, since both of them are rich in plakins and El Bagre-EPF patients present significant antibodies to plakin molecules.

CONCLUSION

In patients with endemic pemphigus foliaceus, we recommend complete isolation of the patient when receiving high dosages of systemic immunosuppressive agents. We further suggest the clinical possibility of a synergistic, fatal interaction between active pemphigus foliaceus, varicella zoster virus, herpes simplex virus, immunosuppressive agents, and a systemic activation of α-1 antitrypsin. Thus, we suggest adequate bed spacing, barrier nursing, and preventative testing for α-1 antitrypsin activation are warranted in these patients to address these complications.

Junctional adhesion molecule overexpression in Kaposi varicelliform eruption skin lesions - as a possible herpes virus entry site

Context:

Herpes simplex virus (HSV) infection of the skin represents a common challenge in dermatology; however, currently the port of viral entry remains obscure. HSV is known to induce an immunoglobulin-binding cell surface receptor in infected cells that utilizes a non-immune mechanism. The replication of HSV in cultured cells is accompanied by the appearance of surface receptors with an affinity for the Fc region of immunoglobulin G.

Case Report:

We describe a 43 year old African American male who presented with a generalized rash, including intense pruritus and umbilicated vesiculopustules. The patient had been previously diagnosed and treated for psoriasis with methotrexate and prednisone. Hematoxylin and eosin demonstrated keratinocytes with ballooning degeneration within the epidermis. Direct immunofluorescence (DIF) results resembled the pattern of paraneoplastic pemphigus, with negative indirect immunofluorescence (IIF) results on rat bladder. Immunohistochemistry revealed deposits of the complement membrane attack complex within dermal sweat glands, as well as the presence of herpes simplex virus 1 on the skin. We report a case of Kaposi varicelliform eruption, a cutaneous eruption caused by a virus infecting patients with pre-existing dermatoses.

Conclusion:

HSV virus infection with over-expression of the junctional adhesion molecule close to herpetic infection sites may preferentially increase viral entry through the skin, possibly triggering a Kaposi varicelliform eruption.

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.

Innate and adaptive immune responses to herpes simplex virus

Immune responses against HSV-1 and HSV-2 are complex and involve a delicate interplay between innate signaling pathways and adaptive immune responses. The innate response to HSV involves the induction of type I IFN, whose role in protection against disease is well characterized in vitro and in vivo. Cell types such as NK cells and pDCs contribute to innate anti-HSV responses in vivo. Finally, the adaptive response includes both humoral and cellular components that play important roles in antiviral control and latency. This review summarizes the innate and adaptive effectors that contribute to susceptibility, immune control and pathogenesis of HSV, and highlights the delicate interplay between these two important arms of immunity.

Herpes simplex virus gD forms distinct complexes with fusion executors gB and gH/gL in part through the C-terminal profusion domain

Herpes simplex virus entry into cells requires a multipartite fusion apparatus made of glycoprotein D (gD), gB, and heterodimer gH/gL. gD serves as a receptor-binding glycoprotein and trigger of fusion; its ectodomain is organized in an N-terminal domain carrying the receptor-binding sites and a C-terminal domain carrying the profusion domain, required for fusion but not receptor binding. gB and gH/gL execute fusion. To understand how the four glycoproteins cross-talk to each other, we searched for biochemical defined complexes in infected and transfected cells and in virions. Previously, interactions were detected in transfected whole cells by split green fluorescent protein complementation (Atanasiu, D., Whitbeck, J. C., Cairns, T. M., Reilly, B., Cohen, G. H., and Eisenberg, R. J. (2007) Proc. Natl. Acad. Sci. U. S. A. 104, 18718-18723; Avitabile, E., Forghieri, C., and Campadelli-Fiume, G. (2007) J. Virol. 81, 11532-11537); it was not determined whether they led to biochemical complexes. Infected cells harbor a gD-gH complex (Perez-Romero, P., Perez, A., Capul, A., Montgomery, R., and Fuller, A. O. (2005) J. Virol. 79, 4540-4544). We report that gD formed complexes with gB in the absence of gH/gL and with gH/gL in the absence of gB. Complexes with similar composition were formed in infected and transfected cells. They were also present in virions prior to entry and did not increase at virus entry into the cell. A panel of gD mutants enabled the preliminary location of part of the binding site in gD to gB to the amino acids 240-260 portion and downstream with Thr304-Pro305 as critical residues and of the binding site to gH/gL at the amino acids 260-310 portion with Pro291-Pro292 as critical residues. The results indicate that gD carries composite-independent binding sites for gB and gH/gL, both of which are partly located in the profusion domain.

Gene delivery using herpes simplex virus vectors

Herpes simplex virus (HSV) is a neurotropic DNA virus with many favorable properties as a gene delivery vector. HSV is highly infectious, so HSV vectors are efficient vehicles for the delivery of exogenous genetic material to cells. Viral replication is readily disrupted by null mutations in immediate early genes that in vitro can be complemented in trans, enabling straightforward production of high-titre pure preparations of non-pathogenic vector. The genome is large (152 Kb) and many of the viral genes are dispensable for replication in vitro, allowing their replacement with large or multiple transgenes. Latent infection with wild-type virus results in episomal viral persistence in sensory neuronal nuclei for the duration of the host lifetime. Transduction with replication-defective vectors causes a latent-like infection in both neural and non-neural tissue; the vectors are non-pathogenic, unable to reactivate and persist long-term. The latency active promoter complex can be exploited in vector design to achieve long-term stable transgene expression in the nervous system. HSV vectors transduce a broad range of tissues because of the wide expression pattern of the cellular receptors recognized by the virus. Increasing understanding of the processes involved in cellular entry has allowed preliminary steps to be taken towards targeting the tropism of HSV vectors. Using replication-defective HSV vectors, highly encouraging results have emerged from recent pre-clinical studies on models of neurological disease, including glioma, peripheral neuropathy, chronic pain and neurodegeneration. Consequently, HSV vectors encoding appropriate transgenes to tackle these pathogenic processes are poised to enter clinical trials.

HSV amplicon-mediated delivery of LIGHT enhances the antigen-presenting capacity of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a B lymphocyte malignancy that remains a largely incurable disease. CLL B cells possess the ability to process and present tumor antigens but lack expression of costimulatory molecules, rendering them inefficient effectors of T-cell activation. We previously demonstrated that helper virus-free preparations of herpes simplex virus (HSV) amplicon vectors encoding CD40L efficiently transduce CLL B cells and render them capable of eliciting specific anti-tumor T-cell responses. LIGHT (TNFSF14), a member of the tumor necrosis factor (TNF) superfamily, efficiently activates both T cells and antigen-presenting cells (APCs). We employed an HSV amplicon vector expressing human LIGHT (hf-HSV-LIGHT) to transduce CLL B cells and compared the immunomodulatory function and T-cell activation induced by hf-HSV-LIGHT transduction to that observed with a CD40L-expressing HSV amplicon (hf-HSV-CD40L). hf-HSV-LIGHT transduction induced expression of endogenous B7.1, B7.2, and ICAM.1 on CLL cells, albeit to a lesser degree than that observed in response to transduction with hf-HSV-CD40L. hf-HSV-LIGHT enhanced the antigen-presenting capacity of CLL B cells, as measured by induction of T-cell proliferation in an allogeneic mixed lymphocyte tumor reaction. Finally, hf-HSV-LIGHT-transduced CLL B cells successfully stimulated the outgrowth of autologous cytotoxic T-lymphocytes in vitro. In aggregate, these data suggest that hf-HSV-LIGHT transduction may be useful for induction of immune responses to CLL and other B-cell lymphoid malignancies.

Identification and expression of human cytomegalovirus transcription units coding for two distinct Fcgamma receptor homologs

Cellular receptors for the Fc domain of immunoglobulin G (IgG) (FcgammaRs) comprise a family of surface receptors on immune cells connecting humoral and cellular immune responses. Several herpesviruses induce FcgammaR activities in infected cells. Here we identify two distinct human cytomegalovirus (HCMV)-encoded vFcgammaR glycoproteins of 34 and 68 kDa. A panel of HCMV strains exhibited a slight molecular microheterogeneity between Fcgamma-binding proteins, suggesting their viral origin. To locate the responsible genes within the HCMV genome, a large set of targeted HCMV deletion mutants was constructed. The mutant analysis allowed the identification of a spliced UL119-UL118 mRNA to encode vFcgammaR gp68 and TRL11/IRL11 to encode vFcgammaR gp34. Both vFcgammaRs are surface resident type I transmembrane glycoproteins. Significant relatedness of sequences in the extracellular chain of gpUL119-118 and gpTRL11 with particular immunoglobulin supergene family domains present in FcgammaR I and FcgammaRs II/III, respectively, indicates a different ancestry and function of gpUL119-118 and gpTRL11. The HCMV-encoded vFcgammaRs highlight an impressive diversification and redundancy of FcgammaR structures.

Targeting gene expression using HSV vectors

Herpes simplex virus (HSV) is an encapsulated DNA virus, with many favourable properties for use as a gene transfer vector. For gene therapy applications, it may be desirable to restrict transgene expression to pre-defined subsets of cells. One potential method for achieving targeted transgene expression using the HSV vector system might involve dictating the cell types to which the vector will transfer the therapeutic transgene of interest. HSV delivers its genetic payload to cells directly through the plasmalemma; the mechanisms are complex and involve multiple viral and cell surface determinants. We have investigated several ways in which each component of the cell entry cascade may be manipulated in order to restrict viral DNA and transgene delivery to particular cellular populations. Our results indicate that targeted transduction may be a viable approach to achieving our goal of targeted HSV-mediated transgene expression.

Characterization of the interaction between the herpes simplex virus type I Fc receptor and immunoglobulin G

Herpes simplex virus type I (HSV-1) virions and HSV-1-infected cells bind to human immunoglobulin G (hIgG) via its Fc region. A complex of two surface glycoproteins encoded by HSV-1, gE and gI, is responsible for Fc binding. We have co-expressed soluble truncated forms of gE and gI in Chinese hamster ovary cells. Soluble gE-gI complexes can be purified from transfected cell supernatants using a purification scheme that is based upon the Fc receptor function of gE-gI. Using gel filtration and analytical ultracentrifugation, we determined that soluble gE-gI is a heterodimer composed of one molecule of gE and one molecule of gI and that gE-gI heterodimers bind hIgG with a 1:1 stoichiometry. Biosensor-based studies of the binding of wild type or mutant IgG proteins to soluble gE-gI indicate that histidine 435 at the CH2-CH3 domain interface of IgG is a critical residue for IgG binding to gE-gI. We observe many similarities between the characteristics of IgG binding by gE-gI and by rheumatoid factors and bacterial Fc receptors such as Staphylococcus aureus protein A. These observations support a model for the origin of some rheumatoid factors, in which they represent anti-idiotypic antibodies directed against antibodies to bacterial and viral Fc receptors.

In vivo immune evasion mediated by the herpes simplex virus type 1 immunoglobulin G Fc receptor

Herpes simplex virus (HSV) glycoproteins gE and gI form an immunoglobulin G (IgG) Fc receptor (FcgammaR) that binds the Fc domain of human anti-HSV IgG and inhibits Fc-mediated immune functions in vitro. gE or gI deletion mutant viruses are avirulent, probably because gE and gI are also involved in cell-to-cell spread. In an effort to modify FcgammaR activity without affecting other gE functions, we constructed a mutant virus, NS-gE339, that has four amino acids inserted into gE within the domain homologous to mammalian IgG FcgammaRs. NS-gE339 expresses gE and gI, is FcgammaR-, and does not participate in antibody bipolar bridging since it does not block activities mediated by the Fc domain of anti-HSV IgG. In vivo studies were performed with mice because the HSV-1 FcgammaR does not bind murine IgG; therefore, the absence of an FcgammaR should not affect virulence in mice. NS-gE339 causes disease at the skin inoculation site comparably to wild-type and rescued viruses, indicating that the FcgammaR- mutant virus is pathogenic in animals. Mice were passively immunized with human anti-HSV IgG and then infected with mutant or wild-type virus. We postulated that the HSV-1 FcgammaR should protect wild-type virus from antibody attack. Human anti-HSV IgG greatly reduced viral titers and disease severity in NS-gE339-infected animals while having little effect on wild-type or rescued virus. We conclude that the HSV-1 FcgammaR enables the virus to evade antibody attack in vivo, which likely explains why antibodies are relatively ineffective against HSV infection.

Partial resistance to gD-mediated interference conferred by mutations affecting herpes simplex virus type 1 gC and gK

Cells expressing herpes simplex virus (HSV) gD can be resistant to HSV entry as a result of gD-mediated interference. HSV strains differ in sensitivity to this interference, which blocks viral penetration but not binding. Previous studies have shown that mutations or variations in virion-associated gD can confer resistance to gD-mediated interference. Here we show that HSV-1 mutants selected for enhanced ability to bind and penetrate in the presence of inhibitory concentrations of heparin were partially resistant to gD-mediated interference. The resistance was largely due to the presence of two mutations: one in gC (the major heparin-binding glycoprotein) resulting in the absence of gC expression and the other in gK resulting in a syncytial phenotype. The results imply that heparin selected for mutants with altered postbinding requirements for entry. Resistance to gD-mediated interference conferred by mutations affecting gC and gK has not been previously described.

The herpes simplex virus-1 glycoprotein E (gE) mediates IgG binding and cell-to-cell spread through distinct gE domains

Herpes simplex virus-1 (HSV-1) glycoprotein E (gE) is a multifunctional protein capable of both binding the Fc portion of IgG and mediating cell-to-cell spread of HSV-1. Here we report that the domain on gE involved in IgG binding is distinct from the domain involved in mediating cell-to-cell spread. To do this we have used five mutants of the HSV-1 strain NS: NS-gE(null), a gE deletion virus; rNS-gE(null), a gE rescued virus; NS-gE339, a gE mutant virus with a four amino acid insert at position 339; rNS-gE339, a gE rescue of NS-gE339; and NS-gE406, a gE mutant virus with the same four amino acids inserted at position 406. Using IgG coated sheep red blood cells in rosetting assays, we show that the NS-gE339 does not bind IgG, yet retains the ability to mediate normal cell-to-cell spread. These results demonstrate that the gE domain involved in IgG binding differs from the domain involved in cell-to-cell spread.

Cross-linking of glycoprotein oligomers during herpes simplex virus type 1 entry

Herpes simplex virus (HSV) has 10 glycoproteins in its envelope. Glycoprotein B (gB), gC, gD, gH, and gL have been implicated in virus entry. We previously used chemical cross-linking to show that these five glycoproteins were close enough to each other to be cross-linked into homodimeric and hetero-oligomeric forms; hetero-oligomers of gB-gC, gC-gD, gD-gB, gH-gL, gC-gL and gD-gL were found in purified virions. To better understand the roles of these glycoproteins in viral entry, we have modified a standard HSV penetration assay to include cross-linkers. This allowed us to examine changes in associations of viral glycoproteins during the entry process. HSV-1(KOS) was adsorbed at 4 degrees C to human neuroblastoma cells (SY5Y). The temperature was raised to 37 degrees C and cells were treated with cross-linker at various times after the temperature shift. Cytoplasmic extracts were examined by Western blotting (immunoblotting) for viral glycoproteins. We found that (i) as in virus alone, the length and concentration of the cross-linking agent affected the number of specific complexes isolated; (ii) the same glycoprotein patterns found in purified virions were also present after attachment of virions to cells; and (iii) the ability to cross-link HSV glycoproteins changed as virus penetration proceeded, e.g., gB and gD complexes which were present during attachment disappeared with increasing time, and their disappearance paralleled the kinetics of penetration. However, this phenomenon appeared to be selective since it was not observed with gC oligomers. In addition, we examined the cross-linking patterns of gB and gD in null viruses K082 and KOSgD beta. Neither of these mutants, which attach but cannot penetrate, showed changes in glycoprotein cross-linking over time. We speculate that these changes are due to conformational changes which preclude cross-linking or spatial alterations which dissociate the glycoprotein interactions during the penetration events.

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.

Disulfide bond structure determination and biochemical analysis of glycoprotein C from herpes simplex virus

A biochemical analysis of glycoprotein C (gC of herpes simplex virus was undertaken to further characterize the structure of the glycoprotein and to determine its disulfide bond arrangement. We used three recombinant forms of gC, gC1(457t), gC1(delta33-123t), and gC2(426t), each truncated prior to the transmembrane region. The proteins were expressed and secreted by using a baculovirus expression system and have been shown to bind to monoclonal antibodies which recognize discontinuous epitopes and to complement component C3b in a dose-dependent manner. We confirmed the N-terminal residues of each mature protein by Edman degradation and confirmed the internal deletion in gC1(delta33-123t). The molecular weight and extent of glycosylation of gC1 (457t), gC1(delta33-123t), and gC2(426t) were determined by treating each protein with endoglycosidases and then subjecting it to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric analysis. The data indicate that eight to nine of the predicted N-linked oligosaccharide sites on gC1(457t) are occupied by glycans of approximately 1,000 Da. In addition, O-linked oligosaccharides are present on gC1(457t), primarily localized to the N-terminal region (amino acids [aa] 33 to 123) of the protein. gC2(426t) contains N-linked oligosaccharides, but no O-linked oligosaccharides were detected. To determine the disulfide bond arrangement of the eight cysteines of gC1(457t),the protein was cleaved with cyanogen bromide. SDS-PAGE analysis followed by Edman degradation identified three cysteine-containing fragments which are not connected by disulfide linkages. Chemical modification of cysteines combined with matrix-assisted laser desorption ionization mass spectrometry identified disulfide bonds between cysteine 1 (aa 127) and cysteine 2 (aa 144) and between cysteine 3 (aa 286) and cysteine 4 (aa 347). Further proteolysis of the cyanogen bromide-generated fragment containing cysteine 5 through cysteine 8, combined with mass spectrometry and Edman degradation, showed that disulfide bonds link cysteine 5 (aa 386) to cysteine 8 (aa 442) and cysteine 6 (aa 390) to cysteine 7 (aa 419). A similar disulfide bond arrangement is postulated to exist in gC homologs from other herpesviruses.

Role of tight junctions of polarized epithelial MDCK cells in the replication of herpes simplex virus type 1

Before completion of polarization, Madin-Darby canine kidney (MDCK) cells showed high infectivity and progeny production of herpes simplex virus type 1 infection. After polarization or formation of tight junctions, the infectivity and virus replication in MDCK cells was restricted significantly. The disruption of tight junctions by depletion of Ca2+ resulted in increasing virus infectivity and productivity. Mechanical disruption of tight junctions by scratching the cell monolayers with injection needle allowed markedly the replication of HSV-1 in the cells aligned along the injured area. In polarized MDCK cells the progeny were released preferentially from the apical surface of the cells. These data suggest that because polarized MDCK cells mimic the epithelial cell layers, this cell line is helpful for determining the factors which regulate viral transmission in the human body.

Sequential isolation of proteoglycan synthesis mutants by using herpes simplex virus as a selective agent: evidence for a proteoglycan-independent virus entry pathway

A novel mouse L-cell mutant cell line defective in the biosynthesis of glycosaminoglycans was isolated by selection for cells resistant to herpes simplex virus (HSV) infection. These cells, termed sog9, were derived from mutant parental gro2C cells, which are themselves defective in heparan sulfate biosynthesis and 90% resistant to HSV type 1 (HSV-1) infection compared with control L cells (S. Gruenheid, L. Gatzke, H. Meadows, and F. Tufaro, J. Virol. 67:93-100, 1993). In this report, we show that sog9 cells exhibit a 3-order-of-magnitude reduction in susceptibility to HSV-1 compared with control L cells. In steady-state labeling experiments, sog9 cells accumulated almost no [35S]sulfate-labeled or [6-3H]glucosamine-labeled glycosaminoglycans, suggesting that the initiation of glycosaminoglycan assembly was specifically reduced in these cells. Despite these defects, sog9 cells were fully susceptible to vesicular stomatitis virus (VSV) and permissive for both VSV and HSV replication, assembly, and egress. HSV plaques formed in the sog9 monolayers in proportion to the amount of input virus, suggesting the block to infection was in the virus entry pathway. More importantly, HSV-1 infection of sog9 cells was not significantly reduced by soluble heparan sulfate, indicating that infection was glycosaminoglycan independent. Infection was inhibited by soluble gD-1, however, which suggests that glycoprotein gD plays a role in the infection of this cell line. The block to sog9 cell infection by HSV-1 could be eliminated by adding soluble dextran sulfate to the inoculum, which may act by stabilizing the virus at the sog9 cell surface. Thus, sog9 cells provide direct genetic evidence for a proteoglycan-independent entry pathway for HSV-1, and results with these cells suggest that HSV-1 is a useful reagent for the direct selection of novel animal cell mutants defective in the synthesis of cell surface proteoglycans.

Studies of protein A and herpes simplex virus-1 induced Fc gamma-binding specificities. Different binding patterns for IgG3 from Caucasian and Oriental subjects

Herpes simplex virus type 1 (HSV-1) expresses a receptor that binds the Fc portion of IgG. This HSV-1 Fc gamma-binding protein is, like protein A of Staphylococcus aureus, known to bind human IgG1, IgG2 and IgG4 but not IgG3 subclasses. However, IgG3 with the allotype Gm(s+)(t+), prominent in the Oriental population, reacts with protein A. This prompted us to investigate the reactivity of Oriental IgG3 monoclonal myeloma proteins of various allotypes with the HSV-1 Fc gamma-binding protein. Of seven Oriental IgG3 myeloma proteins with allotypes Gm(s+)(t+)(u-)(b+)(g-), Gm(s-)(t-)(u+)(b+)(g-) and Gm(s-)(t-)(u+)(b-)(g+), all reacted with the HSV-1 Fc gamma-binding protein. This was in contrast to negative reactions obtained with three IgG3 myeloma proteins of Caucasian origin with Gm(b+)(g-) or Gm(b-)(g+) phenotypes. The same binding pattern, i.e. binding of IgG3 of Oriental but not of Caucasian origin, was found with protein A. The binding of the monoclonal Oriental IgG3 proteins was again independent of the G3m phenotype. These findings support the concept that the HSV-1 Fc gamma-binding protein A have a similar binding site on the IgG molecule. All monoclonal IgG3 proteins derived from Oriental subjects with or without histidine at position 435 bound to HSV Fc gamma-binding protein. This suggests that Oriental IgG3 myeloma proteins with Gm(s-)(t-) phenotypes have additional critical amino acid residue substitutions important for HSV Fc gamma binding different from those already known.

Fv structure of monoclonal antibody II-481 against herpes simplex virus Fc gamma-binding glycoprotein gE contains immunodominant complementarity determining region epitopes that react with human immunoglobulin M rheumatoid factors

Human immunoglobulin M (IgM) rheumatoid factors (RFs) show primary direct enzyme-linked immunosorbent assay (ELISA) reactivity with Fab rather than Fc fragments of monoclonal antibody (mAb) II-481 directed against the Fc gamma-binding site of herpes simplex virus glycoprotein gE. This preferential anti-Fab specificity suggests that RFs react with antigen-binding portions of mAb II-481 as anti-idiotypic antibodies directed at the combining site regions of mAb reacting with the Fc gamma-binding region of gE. Analysis of this idiotype-anti-idiotype reaction employed polymerase chain reaction amplification and sequencing of the variable heavy and light (VH and VL) regions of mAb II-481. When VH and VL regions of mAb II-481 were synthesized as overlapping 7-mer peptides on polypropylene pins, a panel of 10 polyclonal and 6 monoclonal human IgM RFs reacted primarily with epitopes within the three solvent-exposed mAb II-481 complementarity determining regions (CDRs). Preincubation of single CDR heptamer peptides with IgM RFs in free solution, resulted in 63-100% inhibition of RF binding to mAb II-481 on the ELISA plate, confirming the antigenic importance of linear CDR regions for RF reactivity. Combinations of two or three CDR peptides frequently produced 94-100% inhibition of RF binding to whole mAb II-481. Control peptides, singly or in combination, showed no inhibition. Computer modeling suggested that the RF-reactive mAb II-481 Fv region and a previously demonstrated RF-reactive CH3 epitope displayed considerable three-dimensional similarities in conformation. These studies may provide insight into limited shape homologies possibly involved in an RF anti-idiotypic reaction.

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.

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.

Herpesviral Fc receptors and their relationship to the human Fc receptors

Nearly two decades ago, it was observed that cells infected with herpes simplex virus (HSV) acquired an IgG Fc binding activity. The properties of the viral Fc receptor (FcR) have now been characterized by several laboratories. The Fc binding activity appears on the surface of the infected cell prior to formation of progeny virions. The FcR induced by HSV has been identified as the HSV glycoprotein, gE. When HSV gE forms a complex with a second HSV glycoprotein, gI, the receptor binds IgG with higher affinity. Varicella-zoster virus (VZV), which is closely related to HSV, has also been shown to induce an FcR. Like the HSV FcR, the FcR specified by VZV possesses characteristics common to viral glycoproteins. VZV encodes two glycoproteins, gpI and gpIV, which are the homologs of HSV gE and gI. The VZV glycoproteins have many properties common to cell surface receptors, including O-linked glycans and phosphorylation sites. However, extensive computer-assisted analyses of the amino acid sequences of VZV gpI and gpIV did not uncover regions of homology to the human cellular Fc receptors for IgG.

Identification and characterization of a novel herpes simplex virus glycoprotein, gK, involved in cell fusion

Antipeptide sera were used to identify a novel glycoprotein encoded by the UL53 gene of herpes simplex virus type 1 (HSV-1). The UL53 gene product is thought to play a central role in regulating membrane fusion because mutations giving rise to the syncytial phenotype, wherein cells are extensively fused, frequently map to this gene. A single 40-kDa protein, designated gK (the ninth HSV-1 glycoprotein to be described), was detected with antipeptide sera in cells infected with both wild-type and syncytial strains of HSV-1 which were labelled with [35S]methionine and [35S]cysteine or with [3H]glucosamine, and this protein was sensitive to treatment of cells with tunicamycin. With all other HSV glycoproteins studied to date, at least two glycosylated species, often differing substantially in electrophoretic mobility, have been observed in infected cells; thus, gK is unusual in this respect. The 40-kDa gK protein was also immunoprecipitated from cells infected with a recombinant adenovirus vector carrying the UL53 gene. Two glycosylated species of 39 and 41 kDa were produced when UL53 mRNA was translated in vitro in the presence of microsomes, and these proteins differed from gK produced in infected cells not only because they possessed different electrophoretic mobilities but also because they were unable to enter gels after being heated. In addition, a 36-kDa protein was detected in extracts from cells infected with HSV-2 with use of these sera.

Structural basis of C3b binding by glycoprotein C of herpes simplex virus

Glycoproteins C (gC) from herpes simplex virus type 1 (HSV-1) and HSV-2, gC-1 and gC-2, bind the human complement fragment C3b, although the two glycoproteins differ in their abilities to act as C3b receptors on infected cells and in their effects on the alternative complement pathway. Previously, we identified three regions of gC-2 (I, II, and III) which are important for C3b binding. In this study, our goal was to identify C3b-binding sites on gC-1 and to continue our analysis of gC-2. We constructed a large panel of mutants by using the cloned gC-1 and gC-2 genes. Most of the mutant proteins were transported to the surface of transiently transfected L cells and reacted with one or more monoclonal antibodies to discontinuous epitopes. By using 31 linker insertion mutants spread across the coding region of gC-1, we identified four regions in the ectodomain of gC-1 which are important for C3b binding, three of which are similar in position to C3b-binding regions I, II, and III of gC-2. Region III shares some similarities with the short consensus repeat found in CR1, the human complement receptor. These were, in part, the targets for construction of 20 single amino acid changes in region III of gC-1 and gC-2. These mutants identified similarities and differences in the C3b-binding properties of gC-1 and gC-2 and suggest that the amino half of region III is more important for C3b binding. However, our results do not support the concept of a structural relationship between the short consensus repeat of CR1 and gC, since mutations of some of the conserved residues, including three of four cysteines in region III, had no effect on C3b binding. Finally, we constructed four deletion mutants of gC-1, including one which lacked residues 33 to 123, as well as residues 367 to 449. This severely truncated molecule, lacking four cysteines and five potential N-linked glycosylation sites, was transported to the cell surface and retained its ability to bind monoclonal antibodies as well as C3b. Thus, the four distinct C3b-binding regions of gC-1 and several epitopes within two different antigenic sites are localized within residues 124 to 366.

Cell surface receptors for herpes simplex virus are heparan sulfate proteoglycans

The role of cell surface heparan sulfate in herpes simplex virus (HSV) infection was investigated using CHO cell mutants defective in various aspects of glycosaminoglycan synthesis. Binding of radiolabeled virus to the cells and infection were assessed in mutant and wild-type cells. Virus bound efficiently to wild-type cells and initiated an abortive infection in which immediate-early or alpha viral genes were expressed, despite limited production of late viral proteins and progeny virus. Binding of virus to heparan sulfate-deficient mutant cells was severely impaired and mutant cells were resistant to HSV infection. Intermediate levels of binding and infection were observed for a CHO cell mutant that produced undersulfated heparan sulfate. These results show that heparan sulfate moieties of cell surface proteoglycans serve as receptors for HSV.

Herpes simplex virus infection can occur without involvement of the fibroblast growth factor receptor

Basic fibroblast growth factor (bFGF) has been reported to block uptake of herpes simplex virus type 1 (HSV-1) and plaque formation on arterial smooth muscle cells, suggesting a role for the bFGF receptor in HSV entry (R. J. Kaner, A. Baird, A. Mansukhani, C. Basilico, B. D. Summers, R. Z. Florkiewicz, and D. P. Hajjar, Science 248:1410-1413, 1990). We confirmed the effect of bFGF on infection of this cell type with HSV-1 and HSV-2 and found the same result with umbilical vein endothelial cells. However, bFGF does not inhibit plaque formation on any other cell type we tested. Furthermore, there is no correlation between the level of expression of the bFGF receptor and the effect of bFGF. HEp-2 and A431 cells express barely detectable levels of receptor, and yet they are fully permissive for HSV infection in a bFGF-insensitive manner. Thus, interaction of virus with the bFGF receptor is not required for infection of many cell types. In addition, infection of smooth muscle cells is not prevented by incubation of virus with an anti-bFGF antibody, arguing against the hypothesis that virion-associated bFGF acts as a bridge between virus and receptor (A. Baird, R. Z. Florkiewicz, P. A. Maher, R. J. Kaner, and D. P. Hajjar, Nature [London] 348:344-346, 1990).

The fibroblast growth factor receptor is not required for herpes simplex virus type 1 infection

The early events mediating herpes simplex virus type 1 (HSV-1) infection include virion attachment to cell surface heparan sulfates and subsequent penetration. Recent evidence has suggested that the high-affinity fibroblast growth factor (FGF) receptor mediates HSV-1 entry. This report presents three lines of experimental evidence showing that the high-affinity FGF receptor is not required for HSV-1 infection. First, rat L6 myoblasts lacking FGF receptors were as susceptible to HSV-1 infection as L6 cells genetically engineered to express the FGF receptor. Second, a soluble FGF receptor fragment that inhibited FGF binding and receptor activation did not inhibit HSV-1 infection. Finally, basic FGF (but not acidic FGF) inhibited HSV-1 infection in L6 cells lacking FGF receptors, presumably by blocking cell surface heparan sulfates also required for HSV-1 infection. These results show that the high-affinity FGF receptor is not required for HSV-1 infection but instead that specific low-affinity basic FGF binding sites are used for HSV-1 infection.

Analysis of the intracellular maturation of the herpes simplex virus type 1 glycoprotein gH in infected and transfected cells

We have expressed the HSV-1 glycoprotein, gH, in transiently transfected COS-1 cells. The expressed protein was retained intracellularly, contained unprocessed carbohydrate, and was unrecognized by the monoclonal antibody, LP11. In addition, the protein was aggregated. These properties suggest that unlike other HSV glycoproteins, gH is misfolded in transfected cells. Pulse-chase studies of HSV-1-infected cells indicate that the kinetics of processing of gH are comparable to those of gB, gC, and gD. Rescue studies suggest that gH may interact with another protein during maturation in infected cells. However, we were unable to detect any stable interaction, although analysis of gH on neutral sucrose gradients shortly after synthesis indicated a possible transient association with a high molecular weight molecule or complex. The processing and cell surface expression of gH were also analyzed in HSV-1 virus mutants lacking gB, gC, or gD. Our results indicate that the maturation and cell surface transport of gH did not require the presence of these HSV-1 glycoproteins. In addition, three truncation mutants were constructed by linker insertion mutagenesis. Each of the three truncated proteins was synthesized, but the proteins were aggregated, contained only endo H-sensitive carbohydrate, and none were secreted.

Rheumatoid factors react with Fab fragments of monoclonal antibodies to herpes simplex virus types 1 and 2 Fc gamma-binding proteins

Human polyclonal IgM rheumatoid factors (RF) were tested in an enzyme-linked immunosorbent assay with monoclonal antibodies (MAb) (II-481 and B10/A8) to glycoprotein E (gE), the Fc gamma-binding protein of herpes simplex virus type 1 (HSV-1), as well as with MAb 88-S to gE of HSV-2. Most of the RF reacted with II-481 and 88-S. Positive reactions were recorded for RF reacting with whole MAb II-481 and 88-S, as well as with their Fab, but not their Fc, fragments. Human monoclonal IgM RF isolated from mixed cryoglobulins showed a similar profile, with reactivity for both whole MAb II-481 and 88-S and for their Fab fragments. Reactivity with MAb to gE was observed regardless of the Gm specificity of the polyclonal RF and the cross-reactive idiotypes (6B6, 17.109, or G6) of the monoclonal RF. No positive reactions were noted between protein A and Fab fragments of any of the anti-gE MAb. These findings indicate that many RF may bear the internal image of the Fc gamma-binding regions of 2 different herpesviruses: HSV-1 and HSV-2.

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.

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.

Herpes simplex virus IgG Fc receptors induced using recombinant adenovirus vectors expressing glycoproteins E and I

Evidence has been presented that herpes simplex virus (HSV) immunoglobulin (IgG) Fc receptors are composed of a complex of two glycoproteins, gE and gI. In previous studies, cells infected with HSV-1 mutants lacking either gE or gI bound lower levels of soluble IgG than cells infected with wild-type viruses suggesting that both gE and gI were required for IgG binding. We have reevaluated the Fc receptor activity of these mutants using a more sensitive assay involving IgG-coated erythrocytes and have found that cells infected with a gE- mutant HSV-1 did not bind IgG-coated erythrocytes whereas cells infected with a gI- mutant retained some Fc binding activity. To further study HSV-induced Fc receptors recombinant adenovirus vectors expressing gE or gI were constructed. Cells expressing gE alone bound both soluble IgG and IgG-coated red cells, although the binding was consistently lower than that observed with HSV-infected cells or cells expressing both gE and gI. Cells expressing only gI were unable to bind either soluble IgG or IgG-coated erythrocytes. These results support the conclusion that both gE and gI are required for full Fc receptor activity, although gE alone can bind IgG to a lesser extent.

Characterization of herpes simplex virus type 1-induced Fc receptor in its interaction with rabbit immunoglobulin G (IgG)

Herpes simplex virus (HSV) induces a receptor on infected cells that is able to bind the Fc part of immunoglobulin G (IgG). We have examined some basic physicochemical and binding properties of the Fc receptor induced on HSV-1 infected green monkey kidney (GMK) cells in its interaction with rabbit IgG. Fixation of HSV-1 infected cells with glutaraldehyde, formaldehyde, acetone or ethanol did not inhibit the Fc binding ability. The binding specificity of the receptor was not affected by ethanol treatment and all subsequent binding studies were performed with cells treated with ethanol. The receptor was detected within 4 hours of infection and the binding increased until 16 hours post infection. The interaction between ligand and receptor was dependent on pH with a binding optimum around pH 8.0 and 8.5. EDTA, but not EGTA, inhibited receptor binding, suggesting participation of divalent cations in the receptor-ligand interaction. Inhibition of binding was also seen when cells were preincubated for 30 min at 56 degrees, 60 degrees and 100 degrees C in contrast with cells incubated at 37 degrees and 45 degrees C. The number of binding sites on ethanol-treated GMK cells 18 hours after infection was estimated to be around 4 x 10(6)/cell and the affinity constant at approximately 2 x 10(7) M-1.

Identification of herpes simplex virus type 1 glycoproteins interacting with the cell surface

To investigate the interaction of herpes simplex virus type 1 (HSV-1) with the cell surface, we studied the formation of complexes by HSV-1 virion proteins with biotinylated cell membrane components. HSV-1 virion proteins reactive with surface components of HEp-2 and other cells were identified as gC, gB, and gD. Results from competition experiments suggested that binding of gC, gB, and gD occurred in a noncooperative way. The observed complex formation could be specifically blocked by monospecific rabbit antisera against gB and gD. The interaction of gD with the cell surface was also inhibited by monoclonal antibody IV3.4., whereas other gD-specific monoclonal antibodies, despite their high neutralizing activity, were not able to inhibit this interaction. Taken together, these data provide direct evidence that at least three of the seven known HSV-1 glycoproteins are able to form complexes with cellular surface structures.

Soluble forms of herpes simplex virus glycoprotein D bind to a limited number of cell surface receptors and inhibit virus entry into cells

Herpes simplex virus type 1 (HSV-1) and HSV-2 plaque production was inhibited by treating cells with soluble forms of HSV-1 glycoprotein D (gD-1t) and HSV-2 glycoprotein D (gD-2t). Both glycoproteins inhibited entry of HSV-1 and HSV-2 without affecting virus adsorption. In contrast, a soluble form of HSV-2 glycoprotein B had no effect on virus entry into cells. Specific binding of gD-1t and gD-2t to cells was saturable, and approximately 4 x 10(5) to 5 x 10(5) molecules bound per cell. Binding of gD-1t was markedly reduced by treating cells with certain proteases but was unaffected when cell surface heparan sulfate glycosaminoglycans were enzymatically removed or when the binding was carried out in the presence of heparin. Together, these results suggest that gD binds to a limited set of cell surface receptors which may be proteins and that these interactions are essential for subsequent virus entry into cells. However, binding of gD to its receptors is not required for the initial adsorption of virus to the cell surface, which involves more numerous sites (probably including heparan sulfate) than those which mediate gD binding.

Identification of C3b-binding regions on herpes simplex virus type 2 glycoprotein C

Glycoprotein C from herpes simplex viruses types 1 and 2 (gC-1 and gC-2) acts as a receptor for the C3b fragment of the third component of complement. Our goal is to identify domains on gC involved in C3b receptor activity. Here, we used in-frame linker-insertion mutagenesis of the cloned gene for gC-2 to identify regions of the protein involved in C3b binding. We constructed 41 mutants of gC-2, each having a single, double, or triple insertion of four amino acids at sites spread across the protein. A transient transfection assay was used to characterize the expressed mutant proteins. All of the proteins were expressed on the transfected cell surface, exhibited processing of N-linked oligosaccharides, and bound one or more monoclonal antibodies recognizing distinct antigenic sites on native gC-2. This suggested that each of the mutant proteins was folded into a native structure and that a loss of C3b binding by any of the mutants could be attributed to the disruption of a specific functional domain. When the panel of insertion mutants was assayed for C3b receptor activity, we identified three distinct regions that are important for C3b binding, since an insertion within those regions abolished C3b receptor activity. Region I was located between amino acids 102 and 107, region II was located between residues 222 and 279, and region III was located between residues 307 and 379. In addition, region III has some structural features similar to a conserved motif found in complement receptor 1, the human C3b receptor. Finally, blocking experiments indicated that gC-1 and gC-2 bind to similar locations on the C3b molecule.

Deletions in herpes simplex virus glycoprotein D define nonessential and essential domains

Herpes simplex virus glycoprotein D (gD) is a major component of the virion envelope and infected cell membranes and is essential for virus entry into cells. We have recently shown that gD interacts with a limited number of cell surface receptors which are required for virus penetration into cells. To define domains of gD which are required for aspects of virus replication including receptor binding, deletion mutations of 5 to 14 amino acids were constructed by using oligonucleotide-directed mutagenesis. Plasmids containing mutant genes for gD were assayed for the ability to rescue a recombinant virus, F-gD beta, in which beta-galactosidase sequences replace gD-coding sequences. Effects on global folding and posttranslational processing of the molecules were assessed by using a panel of monoclonal antibodies which recognize both continuous and discontinuous epitopes. A region near the amino terminus (residues 7 to 21) of gD which is recognized by monoclonal antibodies able to neutralize herpes simplex virus in the absence of complement was not essential for function. In addition, virtually all of the cytoplasmic domain of gD and an extracellular domain close to the membrane were dispensable. In contrast, deletion mutations in the central region of the molecule, save for one exception, led to alterations in global folding of the molecule and maturation of the protein was inhibited.

Localization on the herpes simplex virus type 1 genome of a region encoding proteins involved in adsorption to the cellular receptor

We have previously shown that aminoglycosides such as neomycin and the polyamino acids polylysine and polyarginine selectively inhibit the binding of herpes simplex virus type 1 (HSV-1) to the cellular receptor, whereas HSV-2 infection is unaffected. In the present study we took advantage of this difference between HSV-1 and HSV-2 by using HSV(-1)-HSV(-2) intertypic recombinants to locate a region on the HSV-1 genome encoding proteins affecting the binding of the virion to the cellular receptor. The results were consistent with those obtained by marker rescue experiments. The identified region, which mapped between coordinates 0.580 and 0.687, contains two partial and eight complete genes, including the glycoprotein C (gC) gene and two others with potential transmembrane sequences. Various gC monoclonal antibody-resistant mutants of HSV-1 as well as a mutant completely lacking gC were found to be fully sensitive to neomycin, suggesting that gC is not the site of drug sensitivity and is not essential for adsorption of virus to the cellular receptor. However, the rate of adsorption was reduced in the absence of gC, indicating a facilitating function of the glycoprotein. The universal nature of this HSV-1 receptor binding was revealed by the similarity in drug sensitivity of infectivity in four different cell lines from various tissues and species.

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.

Interaction of glycoprotein gIII with a cellular heparinlike substance mediates adsorption of pseudorabies virus

Glycoprotein gIII is one of the major envelope glycoproteins of pseudorabies virus (PrV) (Suid herpesvirus 1). Although it is dispensable for viral growth, it has been shown to play a prominent role in the attachment of the virus to target cells, since gIII- deletion mutants are severely impaired in adsorption (C. Schreurs, T. C. Mettenleiter, F. Zuckermann, N. Sugg, and T. Ben-Porat, J. Virol. 62:2251-2257, 1988). We show here that during the process of adsorption of PrV, the viral glycoprotein gIII interacts with a cellular heparinlike receptor. This conclusion is based on the following findings. (i) Heparin inhibits plaque formation of PrV by preventing the adsorption of wild-type virions to target cells. However, heparin does not interfere with the plaque formation of PrV mutants that lack glycoprotein gIII. (ii) Wild-type virions readily adsorb to matrix-bound heparin, whereas gIII- mutants do not. (iii) Pretreatment of cells with heparinase reduces considerably the ability of wild-type PrV to adsorb to these cells and to form plaques but does not negatively affect gIII- mutants. (iv) Glycoprotein gIII binds to heparin and appears to do so in conjunction with glycoprotein gII. Although heparin significantly reduces the adsorption of wild-type virus to all cell types tested, quantitative differences in the degree of inhibition of virus adsorption by heparin to different cell types were observed. Different cell types also retain their abilities to adsorb wild-type PrV to a different extent after treatment with heparinase and differ somewhat in their relative abilities to adsorb gIII- mutants. Our results show that while the primary pathway of adsorption of wild-type PrV to cells occurs via the interaction of viral glycoprotein gIII with a cellular heparinlike receptor, an alternative mode of adsorption, which is not dependent on either component, exists. Furthermore, the relative abilities of different cell types to adsorb PrV by the gIII-dependent or the alternative mode vary to some extent.

Human herpesviruses: a consideration of the latent state

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Herpes simplex type 1-induced Fc receptor binds to the Cgamma2-Cgamma3 interface region of IgG in the area that binds staphylococcal protein A

The binding site of immunoglobulin G (IgG) to herpes simplex virus (HSV) type 1-induced Fc receptor was investigated using human IgG Fc intermediate (Fc(i)) fragments, fragment D of staphylococcal protein A (SPA) and chemically modified human IgG. Human IgG Fc(i) fragment composed of one Cgamma2 and two Cgamma3 domains, bound strongly to HSV-1-infected cells. Fragment D, a monovalent subunit of SPA, inhibited the binding of radiolabelled human IgG Fc fragments to the HSV Fc receptor. Reductively methylated human IgG reacted equally well to HSV-infected cells, as did chemically unmodified IgG in contrast to N-acetylimidazole-modified and diethylpyrocarbonate-modifed human IgG, which were unreactive. These results suggest a similar binding site on human IgG for SPA and the HSV-1 Fc receptor with involvement of the amino acid residues Tyr and His but not Lys. The similarities of binding sites on the IgG molecule for the HSV-1 Fc receptor and rheumatoid factors (RF) may be important for understanding the mechanism of RF production in rheumatoid arthritis or other disease states.