Expression of seven herpes simplex virus type 1 glycoproteins (gB, gC, gD, gE, gG, gH, and gI): comparative protection against lethal challenge in mice.

We have constructed recombinant baculoviruses individually expressing seven of the herpes simplex virus type 1 (HSV-1) glycoproteins (gB, gC, gD, gE, gG, gH, and gI). Vaccination of mice with gB, gC, gD, gE, or gI resulted in production of high neutralizing antibody titers to HSV-1 and protection against intraperitoneal and ocular challenge with lethal doses of HSV-1. This protection was statistically significant and similar to the protection provided by vaccination with live nonvirulent HSV-1 (90 to 100% survival). In contrast, vaccination with gH produced low neutralizing antibody titers and no protection against lethal HSV-1 challenge. Vaccination with gG produced no significant neutralizing antibody titer and no protection against ocular challenge. However, gG did provide modest, but statistically significant, protection against lethal intraperitoneal challenge (75% protection). Compared with the other glycoproteins, gG and gH were also inefficient in preventing the establishment of latency. Delayed-type hypersensitivity responses to HSV-1 at day 3 were highest in gG-, gH-, and gE-vaccinated mice, while on day 6 mice vaccinated with gC, gE, and gI had the highest delayed-type hypersensitivity responses. All seven glycoproteins produced lymphocyte proliferation responses, with the highest response being seen with gG. The same five glycoproteins (gB, gC, gD, gE, and gI) that induced the highest neutralization titers and protection against lethal challenge also induced some killer cell activity. The results reported here therefore suggest that in the mouse protection against lethal HSV-1 challenge and the establishment of latency correlate best with high preexisting neutralizing antibody titers, although there may also be a correlation with killer cell activity.     

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.     

Expression of herpes simplex virus glycoprotein D on antigen presenting cells infected with vaccinia recombinants and protective immunity

We studied the effect of the temporal regulation of herpes simplex virus (HSV) type 1 glycoprotein D (gD-1) expression in Ia⁺ epidermal cells (EC) and macrophages on virus specific immunity and protection from HSV-2 challenge. gD-1 was expressed on the surface of cells infected with a vaccinia recombinant containing gD-1 under the control of an early vaccinia virus promoter (VP176). It was not expressed in cells infected with a recombinant (VP254) in which gD-1 is controlled by a late vaccinia virus promoter. BALB/c mice immunized with both recombinants seroconverted to HSV-2 as determined by neutralization. However, HSV specific delayed type hypersensitivity (DTH) responses were significantly (p<0.025) higher in VP176 than VP254 immunized animals. Both VP176 and VP254 immunized mice were protected from severe neurological disease due to HSV-2 challenge at 14 days post immunization, but long term protection was observed only in VP176 immunized mice.     

Use of lambda gt11 to isolate genes for two pseudorabies virus glycoproteins with homology to herpes simplex virus and varicella-zoster virus glycoproteins.

A library of pseudorabies virus (PRV) DNA fragments was constructed in the expression cloning vector lambda gt11. The library was screened with antisera which reacted with mixtures of PRV proteins to isolate recombinant bacteriophages expressing PRV proteins. By the nature of the lambda gt11 vector, the cloned proteins were expressed in Escherichia coli as beta-galactosidase fusion proteins. The fusion proteins from 35 of these phages were purified and injected into mice to raise antisera. The antisera were screened by several different assays, including immunoprecipitation of [14C]glucosamine-labeled PRV proteins. This method identified phages expressing three different PRV glycoproteins: the secreted glycoprotein, gX; gI; and a glycoprotein that had not been previously identified, which we designate gp63. The gp63 and gI genes map adjacent to each other in the small unique region of the PRV genome. The DNA sequence was determined for the region of the genome encoding gp63 and gI. It was found that gp63 has a region of homology with a herpes simplex virus type 1 (HSV-1) protein, encoded by US7, and also with varicella-zoster virus (VZV) gpIV. The gI protein sequence has a region of homology with HSV-1 gE and VZV gpI. It is concluded that PRV, HSV, and VZV all have a cluster of homologous glycoprotein genes in the small unique components of their genomes and that the organization of these genes is conserved.     

Glycoproteins E and I facilitate neuron-to-neuron spread of herpes simplex virus.

Two herpes simplex virus (HSV) glycoproteins E and I (gE and gI) form a heterooligomer which acts as an Fc receptor and also facilitates cell-to-cell spread of virus in epithelial tissues and between certain cultured cells. By contrast, gE-gI is not required for infection of cells by extracellular virus. HSV glycoproteins gD and gJ are encoded by neighboring genes, and gD is required for both virus entry into cells and cell-to-cell spread, whereas gJ has not been shown to influence these processes. Since HSV infects neurons and apparently spreads across synaptic junctions, it was of interest to determine whether gD, gE, gI and gJ are also important for interneuronal transfer of virus. We tested the roles of these glycoproteins in neuron-to-neuron transmission of HSV type 1 (HSV-1) by injecting mutant viruses unable to express these glycoproteins into the vitreous body of the rat eye. The spread of virus infection was measured in neuron-rich layers of the retina and in the major retinorecipient areas of the brain. Wild-type HSV-1 and a gJ- mutant spread rapidly between synaptically linked retinal neurons and efficiently infected major retinorecipient areas of the brain. gD mutants, derived from complementing cells, infected only a few neurons and did not spread in the retina or brain. Mutants unable to express gE or gI were markedly restricted in their ability to spread within the retina, produced 10-fold-less virus in the retina, and spread inefficiently to the brain. Furthermore, when compared with wild-type HSV-1, gE- and gI- mutants spread inefficiently from cell to cell in cultures of neurons derived from rat trigeminal ganglia. Together, our results suggest that the gE-gI heterooligomer is required for efficient neuron-to-neuron transmission through synaptically linked neuronal pathways.     

采用我国痘苗病毒天坛株载体表达单纯疱疹病毒Ⅰ型糖蛋白D

木文从单纯疱疹病毒Ⅰ型(HSV-1)基因组EcoRI H片段中分离出含有糖蛋白D(gD)基因的2.5kb DWA片段,插入带有痘苗病毒天坛株TK基因区段的pJC—2质粒p7.5k启动子的下游,转染TK~-143细胞,获得带有HSV-1 gD基因的重组痘苗病毒。采用HSV-1 gD单克隆抗体免疫胶体金技术进行电镜观察表明,重组痘苗病毒感染的细胞内有特异性HSV-1 gD抗原.重组病毒免疫家兔后6周可产生明显的HSV-1中和抗体。     

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 (FcγR) 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 FcγR 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 FcγRs. NS-gE₃₃₉ expresses gE and gI, is FcγR⁻, 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 FcγR does not bind murine IgG; therefore, the absence of an FcγR 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 FcγR⁻ 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 FcγR 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 FcγR enables the virus to evade antibody attack in vivo, which likely explains why antibodies are relatively ineffective against HSV infection.     

以痘苗病毒天坛株为载体的表达单纯疱疹病毒Ⅰ型糖蛋白D的重组活疫苗的建立

从我国分离到的一株单纯疱疹病毒Ⅰ型（ＨＳＶ－１－１６８株）病毒基因组中,分离出含有糖蛋白Ｄ（ｇＤ）基因的１．２ｋｂ片段,插入带有痘苗病毒天坛株ＴＫ区的质粒ｐＪＳＢ１１７５Ｐ７．５ｋ启动子下游,转染无白血病鸡胚原代细胞,获得带有ＨＳＶ－１－１６８ｇＤ基因的重组痘苗病毒。此株重组病毒在感染细胞膜上表达ＨＳＶ－１－１６８ｇＤ糖蛋白抗原,能与特异性单克隆抗体反应。在感染细胞中表达的膜抗原经ＳＤＳ－ＰＡＧＥ分析,表达分子量为５４ｋＤ糖蛋白。用Ｓｏｕｔｈｅｒｎ杂交分析了重组病毒ＤＮＡ中特异的ｇＤ基因,对作为活疫苗的重组痘苗病毒株进行了一些微生物学活性、免疫原性和毒力等方面的研究。     

Us3 Kinase Encoded by Herpes Simplex Virus 1 Mediates Downregulation of Cell Surface Major Histocompatibility Complex Class I and Evasion of CD8+ T Cells

Detection and elimination of virus-infected cells by CD8⁺ cytotoxic T lymphocytes (CTLs) depends on recognition of virus-derived peptides presented by major histocompatibility complex class I (MHC-I) molecules on the surface of infected cells. In the present study, we showed that inactivation of the activity of viral kinase Us3 encoded by herpes simplex virus 1 (HSV-1), the etiologic agent of several human diseases and a member of the alphaherpesvirinae, significantly increased cell surface expression of MHC-I, thereby augmenting CTL recognition of infected cells in vitro. Overexpression of Us3 by itself had no effect on cell surface expression of MHC-I and Us3 was not able to phosphorylate MHC-I in vitro, suggesting that Us3 indirectly downregulated cell surface expression of MHC-I in infected cells. We also showed that inactivation of Us3 kinase activity induced significantly more HSV-1-specific CD8⁺ T cells in mice. Interestingly, depletion of CD8⁺ T cells in mice significantly increased replication of a recombinant virus encoding a kinase-dead mutant of Us3, but had no effect on replication of a recombinant virus in which the kinase-dead mutation was repaired. These results indicated that Us3 kinase activity is required for efficient downregulation of cell surface expression of MHC-I and mediates evasion of HSV-1-specific CD8⁺ T cells. Our results also raised the possibility that evasion of HSV-1-specific CD8⁺ T cells by HSV-1 Us3-mediated inhibition of MHC-I antigen presentation might in part contribute to viral replication in vivo.     

Protection against recurrent ocular herpes simplex virus type 1 disease after therapeutic vaccination of latently infected mice

The potential of therapeutic vaccination of animals latently infected with herpes simplex virus type 1 (HSV-1) to enhance protective immunity to the virus and thereby reduce the incidence and severity of recurrent ocular disease was assessed in a mouse model. Mice latently infected with HSV-1 were vaccinated intranasally with a mixture of HSV-1 glycoproteins and recombinant Escherichia coli heat-labile enterotoxin B subunit (rEtxB) as an adjuvant. The systemic immune response induced was characterized by high levels of virus-specific immunoglobulin G1 (IgG1) in serum and very low levels of IgG2a. Mucosal immunity was demonstrated by high levels of IgA in eye and vaginal secretions. Proliferating T cells from lymph nodes of vaccinated animals produced higher levels of interleukin-10 (IL-10) than were produced by such cells from mock-vaccinated animals. This profile suggests that vaccination of latently infected mice modulates the Th1-dominated proinflammatory response usually induced upon infection. After reactivation of latent virus by UV irradiation, vaccinated mice showed reduced viral shedding in tears as well as a reduction in the incidence of recurrent herpetic corneal epithelial disease and stromal disease compared with mock-vaccinated mice. Moreover, vaccinated mice developing recurrent ocular disease showed less severe signs and a quicker recovery rate. Spread of virus to other areas close to the eye, such as the eyelid, was also significantly reduced. Encephalitis occurred in a small percentage (11%) of mock-vaccinated mice, but vaccinated animals were completely protected from such disease. The possible immune mechanisms involved in protection against recurrent ocular herpetic disease in therapeutically vaccinated animals are discussed.     

Synthesis, cellular location, and immunogenicity of bovine herpesvirus 1 glycoproteins gI and gIII expressed by recombinant vaccinia virus.

Two of the major glycoproteins of bovine herpesvirus 1 (BHV-1) are gI, a polypeptide complex with apparent molecular weights of 130,000, 74,000, and 55,000, and gIII (a 91,000-molecular-weight [91K] glycoprotein), which also exists as a 180K dimer. Vaccinia virus (VAC) recombinants were constructed which carry full-length gI (VAC-I) or gIII (VAC-III) genes. The genes for gI and gIII were each placed under the control of the early VAC 7.5K gene promoter and inserted within the VAC gene for thymidine kinase. The recombinant viruses VAC-I and VAC-III retained infectivity and expressed both precursor and mature forms of glycoproteins gI and gIII. The polypeptide backbones, partially glycosylated precursors, and mature gI and gIII glycoproteins were indistinguishable from those produced in BHV-1-infected cells. Consequently, they were apparently cleaved, glycosylated, and transported in a manner similar to that seen during authentic BHV-1 infection, although the processing efficiencies of both gI and gIII were generally higher in recombinant-infected cells than in BHV-1-infected cells. Immunofluorescence studies further demonstrated that the mature gI and gIII glycoproteins were transported to and expressed on the surface of cells infected with the respective recombinants. Immunization of cattle with recombinant viruses VAC-I and VAC-III resulted in the induction of neutralizing antibodies to BHV-1, which were reactive with authentic gI and gIII. These data demonstrate the immunogenicity of VAC-expressed gI and gIII and indicate the potential of these recombinant glycoproteins as a vaccine against BHV-1.     

一种1型单纯庖疹病毒载体系统的建立

1型单纯疱疹病毒（HSV-1）作为溶瘤病毒和病毒载体的研究已有很长的历史. 本研究利用细菌人工染色体技术建立了一种HSV-1载体系统. 首先,将HSV-1内部反向重复序列（internal inverted repeat sequences, IR）两侧的片段克隆入pKO5获得穿梭质粒pKO5/BN,其电转含pHSV-BAC的大肠杆菌后筛选获得删除IR区重组DNA的 pHSVΔIR-BAC. pHSVΔIR-BAC转染Vero细胞获得删除IR区的重组病毒HSVΔIR（MH1001）.上述pKO5/BN和含pHSVΔIR BAC的大肠杆菌构成了HSV-1载体系统. 利用该系统获得了表达绿色荧光蛋白EGFP的重组病毒HSVΔIR/EGFP（MH1002）.MH1001和MH1002在感染的Vero细胞中增殖水平略低于野生型HSV-1,但无显著差异|Western印迹检测表明,重组病毒早期蛋白质ICP0、ICP4、ICP8、ICP22、ICP27在感染细胞中的表达水平下降|免疫荧光及激光共聚焦检测表明,重组病毒与野生型病毒均存在于细胞质中.以上结果表明,删除IR区的重组HSV-1保留了复制能力,能够携载并表达外源基因,建立的HSV-1载体系统可用于构建携载外源基因的复制型重组HSV-1.     

Comparison of adjuvant efficacy of herpes simplex virus type 1 recombinant viruses expressing TH1 and TH2 cytokine genes

The adjuvant effects of cytokines in humoral and cell-mediated immunity to herpes simplex virus type 1 (HSV-1) have been examined in mice using HSV-1 recombinant viruses expressing murine interleukin-2 (IL-2), IL-4, or gamma interferon (IFN-gamma) gene. Groups of naive BALB/c mice were immunized intraperitoneally with one or three doses of the HSV-1 recombinant viruses expressing IL-2, IL-4, or IFN-gamma or with parental control virus. Despite similar replication kinetics, these three recombinant viruses elicited different immune responses to HSV-1 on immunization. Immunization with the recombinant virus expressing IL-4 elicited a humoral response of greater magnitude than immunization with the recombinant viruses expressing IL-2 or IFN-gamma or with parental virus. In contrast, immunization with recombinant virus expressing IL-2 elicited a higher cytotoxic T-cell response than immunization with viruses expressing IL-4 or IFN-gamma. Stimulation in vitro of splenocytes obtained from the mice immunized with UV-inactivated HSV-1 McKrae resulted in a T(H)1 pattern of cytokine expression irrespective of the recombinant virus used in the immunization. As observed for the parental virus, both CD4(+) and CD8(+) T cells contributed equally to the production of IL-2 by the splenocytes of mice immunized with any of the three recombinant viruses. However, the pattern of IFN-gamma production by CD4(+) and CD8(+) T cells differed according to the recombinant virus used. After lethal ocular challenge, all immunized mice were protected completely against death and manifestations of eye disease caused by HSV-1, which are typical responses in unimmunized mice. Mice immunized with IL-4-expressing virus cleared the virus from their eyes more rapidly than mice immunized with IL-2- or IFN-gamma-expressing virus. Taken together, our results suggest that, in contrast to IFN-gamma which did not exhibit an adjuvant effect, both IL-4 and IL-2 act as adjuvants in immunization with HSV, with IL-4 showing greater efficacy.     

Varicella-zoster virus glycoprotein I is essential for growth of virus in Vero cells.

Varicella-zoster virus (VZV) encodes at least six glycoproteins. Glycoprotein I (gI), the product of open reading frame 67, is a 58- to 62-kDa glycoprotein found in VZV-infected cells. We constructed two VZV gI deletion mutants. Immunoprecipitation of VZV gE from infected cells indicated that cells infected with VZV deleted for gI expressed a gE that was larger (100 kDa) than that expressed in cells infected with the parental virus (98 kDa). Cell-associated or cell-free VZV deleted for gI grew to lower titers in melanoma cells than did parental VZV. While VZV deleted for gI replicated in other human cells, the mutant virus replicated to very low titers in primary guinea pig and monkey cells and did not replicate in Vero cells. When compared with the parental virus, rescued viruses, in which the gI deletion was restored with a wild-type allele, showed a similarly sized gE and comparable growth patterns in melanoma and Vero cells. VZV deleted for gI entered Vero cells; however, viral DNA synthesis was impaired in these cells. The VZV gI mutant was slightly impaired for adsorption to human cells. Thus, VZV gI is required for replication of the virus in Vero cells, for efficient replication of the virus in nonhuman cells, and for normal processing of gE.     

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.     

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.     

Noninvasive bioluminescence imaging of herpes simplex virus type 1 infection and therapy in living mice

Mouse models of herpes simplex virus type 1 (HSV-1) infection provide significant insights into viral and host genes that regulate disease pathogenesis, but conventional methods to determine the full extent of viral spread and replication typically require the sacrifice of infected animals. To develop a noninvasive method for detecting HSV-1 in living mice, we used a strain KOS HSV-1 recombinant that expresses firefly (Photinus pyralis) and Renilla (Renilla reniformis) luciferase reporter proteins and monitored infection with a cooled charge-coupled device camera. Viral infection in mouse footpads, peritoneal cavity, brain, and eyes could be detected by bioluminescence imaging of firefly luciferase. The activity of Renilla luciferase could be imaged after direct administration of substrate to infected eyes but not following the systemic delivery of substrate. The magnitude of bioluminescence from firefly luciferase measured in vivo correlated directly with input titers of recombinant virus used for infection. Treatment of infected mice with valacyclovir, a potent inhibitor of HSV-1 replication, produced dose-dependent decreases in firefly luciferase activity that correlated with changes in viral titers. These data demonstrate that bioluminescence imaging can be used for noninvasive, real-time monitoring of HSV-1 infection and therapy in living mice.     

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.