Isolation of a herpes simplex virus-specific antigenic fraction which stimulates the production of neutralizing antibody

Herpes simplex virus Membrane Fusion

Herpes simplex virus mediates multiple distinct fusion events during infection. HSV entry is initiated by fusion of the viral envelope with either the limiting membrane of a host cell endocytic compartment or the plasma membrane. In the infected cell during viral assembly, immature, enveloped HSV particles in the perinuclear space fuse with the outer nuclear membrane in a process termed de-envelopment. A cell infected with some strains of HSV with defined mutations spread to neighboring cells by a fusion event called syncytium formation. Two experimental methods, the transient cell-cell fusion approach and fusion from without, are useful surrogate assays of HSV fusion. These five fusion processes are considered in terms of their requirements, mechanism, and regulation. The execution and modulation of these events require distinct yet often overlapping sets of viral proteins and host cell factors. The core machinery of HSV gB, gD, and the heterodimer gH/gL is required for most if not all of the HSV fusion mechanisms.

Herpesvirus glycoproteins undergo multiple antigenic changes before membrane fusion

Herpesvirus entry is a complicated process involving multiple virion glycoproteins and culminating in membrane fusion. Glycoprotein conformation changes are likely to play key roles. Studies of recombinant glycoproteins have revealed some structural features of the virion fusion machinery. However, how the virion glycoproteins change during infection remains unclear. Here using conformation-specific monoclonal antibodies we show in situ that each component of the Murid Herpesvirus-4 (MuHV-4) entry machinery—gB, gH/gL and gp150—changes in antigenicity before tegument protein release begins. Further changes then occurred upon actual membrane fusion. Thus virions revealed their final fusogenic form only in late endosomes. The substantial antigenic differences between this form and that of extracellular virions suggested that antibodies have only a limited opportunity to block virion membrane fusion.

Understanding HSV-1 entry glycoproteins

Herpes Simplex Virus‐1 is a common infectious agent, but the precise detail of entry and infection of cells has only now begun to be clarified. Four viral surface glycoproteins (gB, gD, gH and gL) are required. This review summarises the known structure and function of each of these essential viral envelope glycoproteins, and explores what is known about their close cooperation with each other in mediating cellular membrane fusion. It is suggested that, following gD binding to one of its entry receptors, membrane fusion is mediated by gB and the heterodimer gH/gL. Significantly, these four entry glycoproteins also play a key role in the interaction between HSV and the host immune system. The glycoproteins serve an important role as targets of adaptive immunity. However, recent studies have demonstrated that the same proteins also play a key role in initiating the early innate immune response to HSV. Understanding the complex functions of these HSV proteins may be essential for successful development of vaccines for HSV. Copyright © 2007 John Wiley & Sons, Ltd.

Cellular and viral requirements for rapid endocytic entry of herpes simplex virus

It was recently demonstrated that herpes simplex virus (HSV) successfully infects Chinese hamster ovary (CHO) cells expressing glycoprotein D (gD) receptors and HeLa cells by an endocytic mechanism (A. V. Nicola, A. M. McEvoy, and S. E. Straus, J. Virol. 77:5324-5332, 2003). Here we define cellular and viral requirements of this pathway. Uptake of intact, enveloped HSV from the cell surface into endocytic vesicles was rapid (t(1/2) of 8 to 9 min) and independent of the known cell surface gD receptors. Following uptake from the surface, recovery of intracellular, infectious virions increased steadily up to 20 min postinfection (p.i.), which corresponds to accumulation of enveloped virus in intracellular compartments. There was a sharp decline in recovery by 30 min p.i., suggesting loss of the virus envelope as a result of capsid penetration from endocytic organelles into the cytosol. In the absence of gD receptors, endocytosed virions did not successfully penetrate into the cytosol but were instead transported to lysosomes for degradation. Inhibitors of phosphatidylinositol (PI) 3-kinase, such as wortmannin, blocked transport of incoming HSV to the nuclear periphery and virus-induced gene expression but had no effect on virus binding or uptake. This suggests a role for PI 3-kinase activity in trafficking of HSV through the cytosol. Viruses that lack viral glycoproteins gB, gD, or gH-gL were defective in transport to the nucleus and had reduced infectivity. Thus, similar to entry via direct penetration at the cell surface, HSV entry into cells by wortmannin-sensitive endocytosis is efficient, involves rapid cellular uptake of viral particles, and requires gB, gD, and gH-gL.

Synthesis, solution structure analysis and antibody binding of cyclic epitope peptides from glycoprotein D of Herpes simplex virus type I

Two cyclic peptides with a thioether bond have been synthesised corresponding to the 9-22 (9LKMADPNRFRGKDL(22)) sequence of glycoprotein D (gD-1) of Herpes simplex virus. The role of the secondary structure in protein-specific monoclonal antibody recognition was investigated. The sequence selected for this study comprises a strongly antigenic site adopting a beta-turn at residues 14Pro-(15)Asn. Thioether bond was formed between the free thiol group of cysteine or homocysteine inserted in position 11 and the chloroacetylated side chain of lysine in position 18. We report here the preparation of cyclic peptides containing Cys or Hcy in position 11, differing only in one methylene group. The linear precursor peptides were synthesised by Boc/Bzl strategy on MBHA resin, and the cyclisation was carried out in alkaline solution. The secondary structure of the peptides was studied by CD, FT-IR and NMR spectroscopy. The CD and FT-IR data have revealed fundamental changes in the solution conformation of the two compounds. The CH(2) group difference significantly resulted in the altered turn structure at the 12Ala and 13Asp as identified by NMR spectroscopy. The antibody binding properties of the cyclopeptides studied by gD-specific monoclonal antibody (A16) in direct and competition enzyme-linked immunosorbent assay (ELISA) were also not the same. We found that peptide LK[HcyADPNRFK]GKDL exhibited higher affinity to Mab A16 than peptide LK[CADPNRFK]GKDL, however, their reactivity was significantly lower compared to the linear ones. Our results clearly show the importance of secondary structure in an antibody binding and demonstrate that even a slight modification of the primary structure dramatically could influence the immune recognition of the synthetic antigens.

Efficacy of a B virus gD DNA vaccine for induction of humoral and cellular immune responses in Japanese macaques

It is desirable to prevent dissemination of B virus (BV) in macaque colonies because transmission of BV to humans causes deadly encephalomyelitis. Vaccination of monkeys is one method that could confine spread of BV within macaque colonies. Availability of a BV DNA vaccine for use in macaques would eliminate the risk of working with infectious BV. Toward this end, we constructed a plasmid expressing the BV glycoprotein D (gD). Immunogenicity of this construct as a DNA vaccine was assessed in adult Japanese macaques by four intracutaneous injections at a dose of 500 microg per head. Results of enzyme-linked immunosorbent assay (ELISA) using a recombinant herpes simplex virus type 1 (HSV1) gD, a homologue of BV gD, showed that significant levels of antibody was induced in all vaccinated animals following each booster injection. Western blot of sera from vaccinated macaques confirmed the specific recognition of authentic BV gD. Immune sera were also demonstrated to contain neutralizing activity against infectious BV. Weak lymphoproliferative responses were also observed in vaccinated macaques using recombinant HSV1 gD as a stimulating antigen and flow cytometry analysis of one individual revealed the presence of HSV1 gD-responsive effector T cells. Thus, the BV gD DNA vaccine was demonstrated to induce both humoral and cellular immune responses in macaques which recognized BV gD.

Monoclonal antibodies to distinct sites on herpes simplex virus (HSV) glycoprotein D block HSV binding to HVEM

HVEM (for herpesvirus entry mediator) is a member of the tumor necrosis factor receptor superfamily and mediates entry of many strains of herpes simplex virus (HSV) into normally nonpermissive Chinese hamster ovary (CHO) cells. We used sucrose density centrifugation to demonstrate that purified HSV-1 KOS virions bind directly to a soluble, truncated form of HVEM (HVEMt) in the absence of any other cell-associated components. Therefore, HVEM mediates HSV entry by serving as a receptor for the virus. We previously showed that soluble, truncated forms of HSV glycoprotein D (gDt) bind to HVEMt in vitro. Here we show that antibodies specific for gD, but not the other entry glycoproteins gB, gC, or the gH/gL complex, completely block HSV binding to HVEM. Thus, virion gD is the principal mediator of HSV binding to HVEM. To map sites on virion gD which are necessary for its interaction with HVEM, we preincubated virions with gD-specific monoclonal antibodies (MAbs). MAbs that recognize antigenic sites Ib and VII of gD were the only MAbs which blocked the HSV-HVEM interaction. MAbs from these two groups failed to coprecipitate HVEMt in the presence of soluble gDt, whereas the other anti-gD MAbs coprecipitated HVEMt and gDt. Previous mapping data indicated that site VII includes amino acids 11 to 19 and site Ib includes 222 to 252. The current experiments indicate that these sites contain residues important for HSV binding to HVEM. Group Ib and VII MAbs also blocked HSV entry into HVEM-expressing CHO cells. These results suggest that the mechanism of neutralization by these MAbs is via interference with the interaction between gD in the virus and HVEM on the cell. Group Ia and II MAbs failed to block HSV binding to HVEM yet still neutralized HVEM-mediated entry, suggesting that these MAbs block entry at a step other than HVEM binding.

Expression and properties of feline herpesvirus type 1 gD (hemagglutinin) by a recombinant baculovirus

We constructed a recombinant baculovirus expressing feline herpesvirus type I (FHV-1) gD in insect cells (Sf9 cells). The expressed product was identified as FHV-1 gD by a panel of monoclonal antibodies specific for the FHV-1 gD, and had an apparent molecular mass of approximately 49 kDa, which was less than that of the authentic FHV-1 gD. When the FHV-1 gD protein were expressed in Sf9 cells and CRFK cells in the presence of tunicamycin, the FHV-1 gD exhibited a molecular mass of 41 kDa. It was shown that the gD protein was transported to the surface of recombinant virus-infected Sf9 cells when examined by membrane-immunofluorescence analysis, and that the gD expressed on the surface of Sf9 cells adsorbed feline erythrocytes. Mice inoculated with a lysate of Sf9 cells expressing FHV-1 gD induced antibodies with virus-neutralizing and hemagglutination-inhibition activities. Therefore, the expressed gD appears to be biologically authentic. These data suggested that recombinant FHV-1 gD produced in Sf9 cells may be a useful immunogen as a feline vaccine.

Disulfide bond structure of glycoprotein D of herpes simplex virus types 1 and 2

Glycoprotein D (gD) is a structural component of the herpes simplex virus envelope which is essential for virus penetration. The function of this protein is highly dependent on its structure, and its structure is dependent on maintenance of three intact disulfide bonds. gD contains six cysteines in its ectodomain whose spacing is conserved among all its homologs in other alphaherpesviruses as well as Marek's disease virus. For other proteins, conservation of cysteine spacing correlates with conservation of disulfide bond structure. We have now solved the disulfide bond structure of gD-1 and gD-2 of herpes simplex virus types 1 and 2, respectively. Two approaches were used. First, we constructed 15 double-Cys mutants of gD-1, representing all possible disulfide pairs. In each case, codons for cysteines were changed to serine. We reasoned that if two cysteines normally form a disulfide bond, double mutations which eliminate one proper bond should be less harmful to gD structure than double mutations which eliminate two disulfide bonds. The mutated genes were cloned into a eucaryotic expression vector, and the proteins were expressed in transiently transfected cells. Three double mutations, Cys-1,5, Cys-2,6, and Cys-3,4 permitted gD-1 folding, processing, transport to the cell surface, and function in virus infection, whereas 12 other double mutations each produced a malfolded and nonfunctional protein. Thus, the three functional double-Cys mutants may represent the actual partners in disulfide bond linkages. The second approach was to define the actual disulfide bond structure of gD by biochemical means. Purified native gD-2 was cleaved by CNBr and proteases, and the peptides were separated by high-performance liquid chromatography. Disulfide-linked peptides were subjected to N-terminal amino acid sequencing. The results show that cysteine 1 (amino acid [aa] 66) is bonded to cysteine 5 (aa 189), cysteine 2 (aa 106) is bonded to cysteine 6 (aa 202), and cysteine 3 (aa 118) is bonded to cysteine 4 (aa 127). Thus, the biochemical analysis of gD-2 agrees with the genetic analysis of gD-1. A similar disulfide bond arrangement is postulated to exist in other gD homologs.

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.

Functional T cell recognition of synthetic peptides corresponding to continuous antibody epitopes of herpes simplex virus type 1 glycoprotein D

Four synthetic peptides which correspond to continuous antibody epitopes of herpes simplex virus (HSV) type 1 glycoprotein D (gD) within amino acid residues 1-23 (8-23), 268-287 and 340-356 were evaluated for in vitro stimulating activity on HSV-primed murine T lymphocytes. All peptides stimulated lymphoproliferative responses and interleukin 2 (IL2) production from draining lymph node (LN) cell populations taken 5 days after footpad immunization with live HSV. Similar responses were elicited from splenic memory T cells only if these T cells were restimulated with HSV in vitro and rested prior to peptide stimulation. Furthermore, peptide stimulated memory T cell populations released soluble factor(s) into the culture supernates which modulated the induced lymphoproliferative and cytotoxic T lymphocyte (CTL) activities of HSV-stimulated, HSV-immune splenocytes (indicator cultures). Memory T cell supernates suppressed lymphoproliferation of indicator cultures, while CTL activity of indicator cultures was either enhanced or suppressed, depending on the peptide and concentration. In contrast, supernates generated by peptide stimulation of draining LN cells had no effect on CTL activity of indicator cultures. However, the lymphoproliferative responses were augmented with three of the four peptides at the highest concentration of peptides tested. Our experiments indicate T helper (Th) and T suppressor (Ts) lymphocyte recognition of four synthetic peptides which encompass continuous antibody epitopes of HSV gD. Immunization with one of these peptides (1-23) induces virus neutralizing antibodies and protection against lethal viral challenge. Th lymphocyte recognition of this peptide in particular, together with its observed function in the induction of protection against HSV infection, indicates that this peptide is a promising candidate as a synthetic vaccine against HSV infection.

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

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

Native and recombinant herpes simplex virus type 1 envelope proteins induce human immune T-lymphocyte responses

The abilities of whole herpes simplex virus type 1 (HSV-1) antigen (HSV-ag) and purified HSV-1 native and recombinant envelope proteins to stimulate in vitro T-lymphocyte responses were compared in patients with recurrent herpes labialis. Immunochemically purified preparations of native glycoproteins B, C, and D (ngB, ngC, ngD) from cultured HSV-1 as well as expressed recombinant plasmid preparations of gD (rgD-1t, rgD-45K) elicited lymphocyte proliferation (LT) and production of gamma interferon (IFN-gamma) and interleukin-2 (IL-2) only in seropositive individuals. The IFN-gamma induced by rgD-1t correlated with the time to the next herpetic lesion in 19 volunteers followed to recurrence (r = 0.69, P less than 0.008), although the magnitude and frequency of LT and IFN-gamma responses were lower with either recombinant or native purified antigens than with the whole-virus antigen. Combinations of ngB plus ngD or ngB plus ngC plus ngD stimulated more IFN-gamma, equivalent to whole-virus-antigen responses. Recombinant-derived human IL-2 also specifically increased LT and IFN-gamma responses in antigen-driven cultures. ngD stimulated IL-2 and LT responses similar to those of whole-virus antigen and higher than those of ngC. HSV-ag and ngB induced significantly higher titers of total IFN than could be accounted for by IFN-gamma; this was not seen for the other antigens, which induced only IFN-gamma. HSV-ag-driven Leu 2a-, plastic-nonadherent blood cells, unlike whole peripheral blood mononuclear cells, showed evidence of an increase and then a decline in the frequency of HSV-responsive cells after a lesion recurrence. These studies suggest that HSV-1 envelope proteins are capable of stimulating an immune T-helper-cell response which is associated with the prevention of human herpes simplex lesion recurrence. Although the whole virus probably contains additional important antigens, increasing concentrations or combinations of certain purified glycoproteins or the addition of nonspecific enhancers of T-lymphocyte function can drive in vitro immune responses to the same level as the complete set of viral antigens.

Herpes simplex virus type 1 glycoprotein E is not indispensable for viral infectivity

A mutant of the herpes simplex virus type 1 Angelotti was isolated in which 87% of the coding region of glycoprotein E (gE) was deleted and replaced by a functional neomycin resistance gene of the Tn5 transposon. The mutant was characterized by restriction enzyme analyses and Southern blotting. Western blotting of proteins and immunofluorescence assays revealed that gE was completely absent and that the Fc receptor was not expressed in cells infected with the mutant. The fact that this mutant was viable and that it replicated to a slightly lower titer than did the wild-type virus suggests that the presence of gE is not a prerequisite of viral infectivity in tissue culture.

Localization of discontinuous epitopes of herpes simplex virus glycoprotein D: use of a nondenaturing ("native" gel) system of polyacrylamide gel electrophoresis coupled with Western blotting

Previously, a panel of monoclonal antibodies (MCAb) was used to define specific epitopes of herpes simplex virus glycoprotein D (gD) (R. J. Eisenberg et al., J. Virol. 53:634-644, 1985). Three groups of antibodies recognized continuous epitopes; group VII reacted with residues 11 to 19 of the mature protein (residues 36 to 44 of the predicted sequence), group II reacted with residues 272 to 279, and group V reacted with residues 340 to 356. Four additional antibody groups recognized discontinuous epitopes of gD, since their reactivity was lost when the glycoprotein was denatured by reduction and alkylation. Our goal in this study was to localize more precisely the discontinuous epitopes of gD. Using a nondenaturing system of polyacrylamide gel electrophoresis ("native" gel electrophoresis) coupled to Western blotting, we analyzed the antigenic activity of truncated forms of gD. These fragments were generated either by recombinant DNA methods or by cleavage of purified native gD-1 (gD obtained from herpes simplex virus type 1) and gD-2 (gD obtained from herpes simplex virus type 2) with Staphylococcus aureus protease V8. Antibodies in groups III, IV, and VI recognized three truncated forms of gD-1 produced by recombinant DNA methods, residues 1 to 287, 1 to 275, and 1 to 233. Antibodies in group I recognized the two larger forms but did not react with the gD-1 fragment of residues 1 to 233. On the basis of these and previous results, we concluded that a protion of epitope I was located within residues 233 to 259 and that epitopes III, IV, and VI were upstream of residue 233. Antibodies to continuous epitopes identified protease V8 fragments of gD-1 and gD-2 that contained portions of either the amino or carboxy regions of the proteins. None of the V8 fragments, including a 34K polypeptide containing residues 227 to 369, reacted with group I antibodies. This result indicated that a second portion of epitope I was located upstream of residue 227. Two amino-terminal fragments of gD-1, 33K and 30K, reacted with group III, IV, and VI antibodies. A 33K fragment of gD-2 reacted with group III antibodies. Based on their size and reactivity with endo-beta-N-acetylglycosaminidase F, we hypothesized that the 33K and 30K molecules represented residues 1 to 226 and 1 to 182 of gD-1, respectively. These results suggest that epitopes III, IV, and VI are located within the first 182 residues of gD.(ABSTRACT TRUNCATED AT 400 WORDS)

The quest for a herpes simplex virus vaccine: background and recent developments

Herpes simplex virus infections in humans range from localized skin infections of the oral, ocular and genital regions, to severe and often fatal disseminated infections of immunocompromised hosts. Following primary infection, the virus often becomes established in a latent form in the neurons of sensory ganglia and can reactivate to excrete virus asymptomatically or produce recrudescent lesions. This review describes some of the mechanisms involved in the immune response against HSV infections and examines the different strategies adopted to develop a vaccine against this seemingly intractable disease.

Helper T cells induced by an immunopurified herpes simplex virus type I (HSV-I) 115 kilodalton glycoprotein (gB) protect mice against HSV-I infection

Three herpes simplex virus type I (HSV-I) glycoproteins of apparent molecular masses 103, 63, and 115 kD have been purified using virus-specific monoclonal antibodies (mAb) G8D1, C2D2, and T157, respectively. Both G8D1 and C2D2 neutralize HSV-I in vitro and passively protect CBA mice against HSV-I infection in vivo, whereas T157 is neither neutralizing nor passively protective. However, mice given a single subcutaneous injection of 30 micrograms 115 kD glycoprotein in saline were completely protected against lethal challenges of HSV-I administered intraperitoneally or in the footpad 7 d after immunization. In contrast, mice similarly immunized with 103 or 63 kD glycoproteins were only partially protected. The prophylactic immunity was correlated with an early induction of specific antibody, which became even more evident 3 d after virus challenge. There was a remarkable similarity in antibody isotype distribution between the responses to 115 kD glycoprotein and to heat-inactivated intact HSV-I. However, the prechallenge sera from 115 kD glycoprotein hyperimmunized mice were again neither virus-neutralizing nor passively protective. All three glycoproteins induced only low levels of delayed-type hypersensitivity (DTH). Pretreatment of mice with cyclophosphamide significantly enhanced DTH to 115 kD and 103 kD glycoproteins in the absence of antibody, but failed to confer significant immunity, indicating that DTH alone is insufficient for protection. Splenic and lymph node Ig- (B cell-depleted) cells from mice protectively immunized with 115 kD glycoprotein could adoptively transfer effective protection and enhance a virus neutralizing antibody response in normal recipients challenged with a lethal dose of HSV-I. Both the protection and the ability to enhance neutralizing antibody were diminished when the cells were treated with mAb GK 1.5 and complement. These results therefore demonstrate that the 115 kD glycoprotein, though not apparently containing accessible epitopes for the induction of virus-neutralizing antibody, possesses determinants capable of activating helper T cells. These L3T4+ cells confer strong protective immunity by enhancing protective antibody upon challenge infection, probably through associative help.

Potent neutralizing activity associated with anti-glycoprotein D specificity among monoclonal antibodies selected for binding to herpes simplex virions

Thirty-three monoclonal antibodies were selected for ability to bind to purified virions of herpes simplex virus and were shown by immunoprecipitation to react with one or another of the envelope glycoproteins. Only six of these antibodies exhibited potent neutralizing activity, and all six were specific for glycoprotein D. Two other anti-glycoprotein D antibodies and 25 antibodies specific for four other viral glycoproteins had much less potent, if any, neutralizing activity.

Human T-lymphocyte response in vitro to synthetic peptides of herpes simplex virus glycoprotein D

Immunization of mice with a synthetic peptide that corresponds to a murine antibody-defined immunodominant domain of herpes simplex virus (HSV) glycoprotein D (gD) induced neutralizing antibodies against HSV types 1 and 2 and protected animals against a lethal challenge with HSV type 2 (Dietzschold, B., Eisenberg, R., Ponce de Leon, M., Golub, E., Hudecz, F., Varicchio, A. & Cohen, G. (1984) J. Virol. 52, 431-435). We report here that human peripheral blood T cells from HSV-seropositive and -seronegative adult donors are activated by this synthetic peptide in vitro. Interleukin-2-dependent T-cell lines established from these cultures respond specifically to peptides containing residues 1-23 of HSV gD and to a panel of overlapping peptides within this domain. The T-cell proliferative response was maximal when the majority of interleukin-2-propagated T cells were of the helper phenotype and the peptides were at least 16 amino acids long. Peptides of 8 or 12 amino acids from the carboxyl terminus were nonstimulatory. Peptide-activated T-cell lines from sero-negative donors less than 11 years old could be established in vitro, but most cells were of the suppressor/cytotoxic phenotype and demonstrated no antigen-specificity when tested with the panel of synthetic peptides.

Localization of epitopes of herpes simplex virus type 1 glycoprotein D

We previously defined eight groups of monoclonal antibodies which react with distinct epitopes of herpes simplex virus glycoprotein D (gD). One of these, group VII antibody, was shown to react with a type-common continuous epitope within residues 11 to 19 of the mature glycoprotein (residues 36 to 44 of the predicted sequence of gD). In the current investigation, we have localized the sites of binding of two additional antibody groups which recognize continuous epitopes of gD. The use of truncated forms of gD as well as computer predictions of secondary structure and hydrophilicity were instrumental in locating these epitopes and choosing synthetic peptides to mimic their reactivity. Group II antibodies, which are type common, react with an epitope within residues 268 to 287 of the mature glycoprotein (residues 293 to 312 of the predicted sequence). Group V antibodies, which are gD-1 specific, react with an epitope within residues 340 to 356 of the mature protein (residues 365 to 381 of the predicted sequence). Four additional groups of monoclonal antibodies appear to react with discontinuous epitopes of gD-1, since the reactivity of these antibodies was lost when the glycoprotein was denatured by reduction and alkylation. Truncated forms of gD were used to localize these four epitopes to the first 260 amino acids of the mature protein. Competition experiments were used to assess the relative positions of binding of various pairs of monoclonal antibodies. In several cases, when one antibody was bound, there was no interference with the binding of an antibody from another group, indicating that the epitopes were distinct. However, in other cases, there was competition, indicating that these epitopes might share some common amino acids.

The effect of some common inactivation procedures on the antigens of bovine herpesvirus 1

Bovine embryonic kidney cells were infected with bovine herpesvirus 1 (BHV1) or were sham-inoculated. When cytopathic effect was apparent, the cells were treated with beta-propiolactone, formalin, heat (56 degrees C), or ultraviolet irradiation until the virus was inactivated. Infected-treated, infected-untreated (IU) and sham-inoculated cultures were solubilized using Triton X-100 detergent. Resulting preparations were tested by 2-dimensional- and fused rocket-immunoelectrophoresis and were evaluated for their ability to inhibit virus neutralization by BHV1 antiserum. Eleven viral antigens were detected consistently in IU preparations, which strongly inhibited virus neutralization. Eight or more IU antigens were detected in beta-propiolactone-treated, formalin-treated and heat-treated preparations; these inhibited virus neutralization less strongly than the IU preparations. No IU antigens were detected in ultraviolet-treated preparations, nor did this material inhibit virus neutralization. One of the IU antigens was reduced preferentially by all treatments. The selective destruction of antigens by the various treatments might allow antigen-specific serological testing to distinguish vaccinated from naturally-exposed cattle.

Glycoprotein D protects mice against lethal challenge with herpes simplex virus types 1 and 2

Glycoprotein D is a virion envelope component of herpes simplex virus types 1 and 2. Sets of mice were immunized with purified gD-1 or gD-2 and were challenged with a lethal dose of herpes simple virus, either type 1 or type 2. All or virtually all of the immunized mice survived challenge with either agent, whereas challenge of sham-immunized mice was almost always fatal. Serum samples taken before challenge contained gD-specific antibodies which had 50% neutralization titers ranging from 1:16 to 1:512 against homologous and heterologous virus types. We conclude that either gD-1 or gD-2 is a potential candidate for a subunit vaccine against herpetic infections.

Amino-terminal sequence of glycoprotein D of herpes simplex virus types 1 and 2

Glycoprotein D (gD) of herpes simplex virus is a structural component of the virion envelope which stimulates production of high titers of herpes simplex virus type-common neutralizing antibody. We carried out automated N-terminal amino acid sequencing studies on radiolabeled preparations of gD-1 (gD of herpes simplex virus type 1) and gD-2 (gD of herpes simplex virus type 2). Although some differences were noted, particularly in the methionine and alanine profiles for gD-1 and gD-2, the amino acid sequence of a number of the first 30 residues of the amino terminus of gD-1 and gD-2 appears to be quite similar. For both proteins, the first residue is a lysine. When we compared our sequence data for gD-1 with those predicted by nucleic acid sequencing, the two sequences could be aligned (with one exception) starting at residue 26 (lysine) of the predicted sequence. Thus, the first 25 amino acids of the predicted sequence are absent from the polypeptides isolated from infected cells.

Localization and synthesis of an antigenic determinant of herpes simplex virus glycoprotein D that stimulates the production of neutralizing antibody

An antigenic determinant capable of inducing type-common herpes simplex virus (HSV)-neutralizing antibodies has been located on glycoprotein D (gD) of HSV type 1 (HSV-1). A peptide of 16 amino acids corresponding to residues 8 to 23 of the mature glycoprotein (residues 33 to 48 of the predicted gD-1 sequence) was synthesized. This peptide reacted with an anti-gD monoclonal antibody (group VII) previously shown to neutralize the infectivity of HSV-1 and HSV-2. The peptide was also recognized by polyclonal antibodies prepared against purified gD-1 but was less reactive with anti-gD-2 sera. Sera from animals immunized with the synthetic peptide reacted with native gD and neutralized both HSV-1 and HSV-2.

Synthesis and processing of glycoprotein D of herpes simplex virus types 1 and 2 in an in vitro system

We carried out studies of in vitro translation and processing of glycoprotein D (gD) of herpes simplex virus types 1 and 2 by using mRNA from cells infected for 6 h and a reticulocyte lysate translation system. Polypeptides of 49,000 daltons were immunoprecipitated with anti-gD-1 sera. Each in vitro-synthesized molecule had the same methionine tryptic peptide profile as the respective in vivo precursors, pgD-1 and pgD-2. In addition, the polypeptides synthesized in vitro were larger than the corresponding molecules synthesized in the presence of tunicamycin. This suggested that each of the gD polypeptides synthesized in vitro contained a transient N-terminal signal sequence. When the translation mixture was supplemented with pancreatic microsomes, each of the gD polypeptides was converted cotranslationally to a larger-molecular-weight form. Processing involved addition of three N-asparagine-linked oligosaccharides and removal of the signal peptide. When trypsin was added after in vitro processing, a polypeptide which was 3,000 daltons smaller than the in vitro-modified form of gD was immunoprecipitated. Experiments with endo-beta-N-acetylglucosaminidase H showed that this polypeptide still contained the three N-asparagine-linked oligosaccharides. Two monoclonal antibodies, 57S (group V) and 17O (group VII), were used to further orient gD in microsomes. The group V determinant was located in the trypsin-sensitive 3,000-dalton fragment, and the group VII determinant was located in the portion of gD which was protected from trypsin. We concluded that gD is oriented with the three glycosylation sites inside the vesicles and that 3,000 daltons containing the group V determinant are located outside. Immunofluorescence studies indicated that the group V determinant of gD is inside the plasma membrane of herpes simplex virus-infected cells and that the group VII determinant is outside. This cellular orientation is consistent with predictions based on the in vitro experiments.

Specific herpes simplex virus antigen in human gingiva

Herpes simplex virus type 1 (HSV-1) specific antigens were found to be present in the sulcular epithelial cells of patients that were undergoing periodontal treatment. Four out of 14 cases were positive to specific HSV-1 antigen, as demonstrated by the indirect immunofluorescent assay. No nuclear staining was seen in any epithelial cells. These observations seem to indicate that the viral genome resides in the sulcular epithelial cells of the gingiva and is possibly localized in the stratum granulosum and spinosum.

The use of monoclonal antibodies in (reverse) passive haemagglutination tests for herpes simplex virus antigens and antibodies

Three monoclonal antibodies against herpes simplex virus type 2 have been tested for their suitability as reagents in reverse passive haemagglutination. Two of these antibodies with specificity for virus glycoprotein D, when linked to red blood cells, were able to capture antigens without being agglutinated, but addition of immune serum subsequently led to agglutination. Haemagglutination using these monoclonal antibody-linked, antigen-captured red cells was readily applicable to testing human sera for antibodies to herpes simplex virus and the titres obtained correlated with those from virus plaque neutralisation tests. The procedure has been termed "Specific Antigen Capture Passive Haemagglutination." A further monoclonal antibody with specificity for the major DNA-binding protein of type 2 herpes virus-infected cells (a nonstructural protein) showed conventional reverse passive haemagglutination when linked to red blood cells and was specific for type 2 herpes simplex virus. The nature and potential uses of these simple reverse passive haemagglutination procedures using monoclonal antibody reagents are discussed.

Purification of glycoprotein gD of herpes simplex virus types 1 and 2 by use of monoclonal antibody

Glycoproteins gD-1 and gD-2 of herpes simplex virus types 1 and 2, respectively, were purified on an immunoadsorbent consisting of the type-common monoclonal antibody HD-1 linked to Sepharose. Each glycoprotein was of sufficient purity, quantity, and biological activity to be used for immunological and biochemical studies. Each glycoprotein induced high titers of type-common monospecific neutralizing antibody in mice. Amino aicd analysis indicated that gD-1 and gD-2 had similar though not identical amino acid compositions.

Effect of monoclonal antibodies on limited proteolysis of native glycoprotein gD of herpes simplex virus type 1

We examined the properties of 17 monoclonal antibodies to glycoprotein gD of herpes simplex type 1 (HSV-1) (gD-1) and HSV-2 (gD-2). The antibodies recognized eight separate determinants of gD, based on differences in radioimmuno-precipitation and neutralization assays. The determinants were distributed as follows: three were gD-1 specific, one was gD-2 specific, and four were type common. Several type-specific and type-common determinants appeared to be involved in neutralization. We developed a procedure for examining the effect that binding of monoclonal antibody has on proteolysis of native gD-1 by Staphylococcus aureus protease V8. We showed that several different patterns of protease V8 cleavage were obtained, depending on the monoclonal antibody used. The proteolysis patterns were generally consistent with the immunological groupings. With four groups of antibodies, we found that fragments of gD-1 remained bound to antibody after V8 treatment. A 38,000-dalton fragment remained bound to antibodies in three different groups of monoclonal antibodies. This fragment appeared to contain one type-common and two type-specific determinants. A 12,000-dalton fragment remained bound to antibodies belonging to one type-common group of monoclonal antibodies. Tryptic peptide analysis revealed that the 12,000-dalton fragment represented a portion of the 38,000-dalton fragment and was enriched in a type-common arginine tryptic peptide.

Monoclonal antibodies to herpes simplex virus type 1 proteins, including the immediate-early protein ICP 4

Monoclonal antibodies were prepared against herpes simplex virus type 1 (strain 14012) by two immunization procedures. Procedure A utilized infectious virus propagated in mouse cells, and procedure B utilized mouse cells infected with herpes simplex virus in the presence of cycloheximide and harvested 1 h after removal of the inhibitor. A total of 52 monoclonal antibodies were obtained against 10 herpes simplex virus proteins, including four glycosylated proteins (a 110,000-molecular-weight protein, gB, gC, and gD) and six nonglycosylated proteins (a 68,000-molecular-weight protein, ICP 9, ICP 8, ICP 6, ICP 5, and the immediate-early ICP 4). The antibodies were assayed against herpes simplex virus types 1 and 2 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radioimmunoprecipitates, immunofluorescence, and neutralization. Using the reagents prepared, we concluded that the 110,000-molecular-weight protein, gD, ICP 9, ICP 9, ICP 6, and the 68,000-molecular-weight protein express both type-specific and cross-reactive antigenic determinants. In contrast, nine antibodies against gB all cross-reacted with herpes simplex virus type 2, whereas eight antibodies to gC all reacted type specifically.

Synthesis and processing of glycoproteins gD and gC of herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) contains five glycoproteins, designated gA, gB, gC, gD, and gE. The present studies focused on the synthesis and processing of two of these, gC and gD. By using monoprecipitin antibody to gC, we demonstrated an antigenic and structural relationship between the precursor, pgC(110), and the product, gC(130). Tryptic peptide analysis showed that pgC and gC shared methionine peptides and that these molecules had the same fingerprint pattern as that of gC(130) extracted from the purified virion. These results suggested that post-translational processing of gC involved no major changes in methionine-containing tryptic peptides or in the cleavage sites required to generate those peptides. The syntheses of gC and gD were compared. We found that the glycoproteins were synthesized starting at different times in the infectious cycle; pgD was detected by 2 h postinfection, whereas pgC was first detected at 4 to 6 h postinfection. Both precursor molecules, pgC(110) and pgD(52), are basic glycopolypeptides, and in both cases processing involved changes in molecular weight and charge. These changes were detected by two-dimensional gel electrophoresis. Both glycoproteins exhibited heterogeneity, displayed as a series of spots (6 for gD and 15 to 20 for gC) of increasing negative charge and molecular weight. Neuraminidase treatment decreased the size, number, and acidic charge of the spots, suggesting that processing was due in part, but not entirely, to addition of sialic acid to pgD and pgC.

Comparative structural analysis of glycoprotein gD of herpes simplex virus types 1 and 2

We studied the synthesis and processing of the type-common glycoprotein gD in herpes simplex virus type 2 (HSV-2) and compared it structurally to glycoprotein gD of herpes simplex virus type 1 (HSV-1). We demonstrated that in HSV-2, gD undergoes posttranslational processing from a lower-molecular-weight precursor (pgD51) to a higher-molecular-weight product (gD56). Tryptic peptide analysis by cation-exchange chromatography indicated that this processing step altered neither the methionine nor the arginine tryptic peptide profile of gD of HSV-2. Comparative tryptic peptide analysis of gD of HSV-1 and HSV-2 showed that the methionine and arginine tryptic peptide profiles of these two proteins were very similar, but not identical. Some of the resolved peptides coeluted from the cation-exchange column, suggesting that some amino acid sequences of the two proteins might be very similar. However, each protein also appeared to possess several type-specific tryptic peptides. The structural similarity of these two glycoproteins correlates well with their antigenic cross-reactivity since monoprecipitin antibody to gD of HSV-1 also immunoprecipitates gD of HSV-2 and neutralizes the infectivity of both viruses to approximately the same extent.

Structural analysis of the capsid polypeptides of herpes simplex virus types 1 and 2

Capsids of herpes simplex virus (HSV) types 1 and 2 contain seven polypeptides ranging in molecular weight from 154,000 to 12,000 (termed NC-1 through NC-7 in order of descending molecular weight). Antibodies prepared to HSV-1 capsid polypeptides isolated from sodium dodecyl sulfate-polyacrylamide gels reacted in an immunofluorescence assay against HSV-1-infected KB cells. Three of the antibodies (anti-NC-1, anti-NC-2, and anti-NC-3,4) also reacted with HSV-2-infected cells. Tryptic peptide analysis showed that each of the HSV-1 capsid polypeptides had a unique methionine peptide profile, and none appeared to be derived from the major capsid polypeptide. Comparative peptide analysis of HSV-1 and HSV-2 showed that one polypeptide (NC-7, 12,000 molecular weight) had an identical methionine peptide profile and a very similar arginine peptide profile in both virus types. The arginine peptide profile of NC-7 of HSV-1 was very different from the arginine profile of KB histone H4. Although there were certain intertypic similarities in the methionine peptide profiles of the other capsid components especially in NC-1 (the major capsid protein), there was no case where the tryptic peptides were identical in the two virus types.

Effect of tunicamycin on herpes simplex virus glycoproteins and infectious virus production

The antibiotic tunicamycin, which blocks the synthesis of glycoproteins, inhibited the production of infectious herpes simplex virus. In the presence of this drug, [14C]glucosamine and [3H]mannose incorporation was reduced in infected cells, whereas total protein synthesis was not affected. Gel electrophoresis of [2-3H]mannose-labeled polypeptides failed to detect glycoprotein D or any of the other herpes simplex virus glycoproteins. By use of specific antisera we demonstrated that in the presence of tunicamycin the normal precursors to viral glycoproteins failed to appear. Instead, lower-molecular-weight polypeptides were found which were antigenically and structurally related to the glycosylated proteins. Evidence is presented to show that blocking the addition of carbohydrate to glycoprotein precursors with tunicamycin results in the disappearance of molecules, possibly due to degradation of the unglycosylated polypeptides. We infer that the added carbohydrate either stabilizes the envelope proteins or provides the proper structure for correct processing of the molecules needed for infectivity.

A type-specific antiserum induced bya major herpesvirus type 1 glycoprotein

A type-specific antiserum was prepared against VP 7/8, the major HSV-1 type-specific glycoprotein. The specificity of this antiserum was demonstrated by both neutralization of HSV-1 infectivity and immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis of the immunoprecipitates. Only minimal cross-reactivity with HSV-2 was observed. This major VP 7/8 glycorprotein was also purified from a host of virus-induced proteins with the specific immunoadsorbent prepared with anti-VP 7/8 serum. The one-step purification of this type-specific neutralizing antigen of HSV-1 should allow the development of a sensitive and specific radioimmunoassay.

Structural analysis of precursor and product forms of type-common envelope glycoprotein D (CP-1 antigen) of herpes simplex virus type 1

The type-common CP-1 antigen of herpes simplex virus type 1 (HSV-1) is associated in the infected cell with two components, a 52,000-molecular-weight glycoprotein (gp52 or pD) and a 59,000-molecular-weight glycoprotein (gp59 or D). The larger form (D) is also found in the virion envelope. It was postulated that pD is a precursor of D. We found that pD shared methionine and arginine tryptic peptides with D isolated from infected cell extracts. D isolated from infected extracts had the same trypric methionine peptide profile as D isolated from the virion envelope. Thus, processing of pD to D does not involve any major alterations in polypeptide structure. Furthermore, D did not share tryptic methionine peptides with the other major glycoproteins of HSV-1. Using [2-3H]mannose as a specific glycoprotein label, we found that pD, which is a basic protein (isoelectric point = 8.0) contained a 1,800-molecular-weight oligomannosyl core moiety and was processed by further glycosylation and sialyation to a more acidic and heterogeneous molecule D, which as a molecular weight of at least 59,000.

Herpes simplex virus replication in pheochromocytoma cell line that responds to nerve growth factor

Cultured cells of neural origin (PC-12, pheochromocytoma cell line) respond to nerve growth factor (NGF) by extending neurites. These cells whether treated with NGF or not can be infected with herpes simplex virus and produce progeny virus. Viral antigens are detected on the cell surface and fusion of cells to form polykaryocytes takes place. Nucleocapsids are found within the cell nucleus and enveloped virus in a present both in the cytoplasm and extracellular space. Virus was not observed within the neurites but laterations in the neurite microtubular structure occurred after infection.

Type-common CP-1 antigen of herpes simplex virus is associated with a 59,000-molecular-weight envelope glycoprotein

The CP-1 antigen of herpes simplex virus type 1 (HSV-1) is a glycoprotein found in the soluble portion of infected cells, in detergent extracts of infected cell membranes, and in the envelope of purified virus. Antisera were prepared against a further purified form of CP-1 prepared from HSV soluble antigen mix; a glycoprotein, gp52, isolated from detergent-treated infected cells; and detergent extracts of purified virus. Each of the antisera reacted with CP-1 to give a single immunoprecipitin band of identity, and each antiserum neutralized the infectivity of HSV-1 and HSV-2. Our results suggested that the type-common determinants involved in the stimulation of neutralizing antibody resided on a 52,000-molecular-weight (52K) glycoprotein. The envelope of HSV contains several glycoproteins: one component at 59K and a complex of two or three components at 130K, none of which corresponds in molecular weight to gp52. Using the antisera as immunological probes, we performed pulse-chase experiments with [(35)S]methionine-labeled HSV-1-infected cells and followed the disposition of the glycoproteins during the infectious cycle. Each antiserum immunoprecipitated a (35)S-labeled 52K protein from lysates of cells pulse-labeled at 5 h after infection. By 10 h, the label was chased into a 59K protein also precipitable by each of the three antisera. The results suggest that gp52 is a precursor of gp59 and that the latter corresponds in molecular weight to one of the major glycoproteins of the virion envelope.

Neutralization of reovirus: the gene responsible for the neutralization antigen

The S1 genome segment of reovirus is linked to type specificity as determined by neutralization antibody. This gene segment codes for a minor outer capsid polypeptide (sigma1). Therefore, sigma1 is the peptide responsible for induction of neutralization antibody and confers type specificity. This biologic property of reovirus was defined using hybrid recombinants clones between reovirus types 1 and 3 and 2 and 3.

Comparison of the virion proteins specified by herpes simplex virus types 1 and 2

Purified herpes simplex virus type 2 (HSV-2) virions were found to contain approximately the same number of polypeptides as HSV type 1 (HSV-1) virions. Comparisons of the structural proteins specified by five independent HSV-2 isolates revealed some minor differences in their electrophoretic profiles on sodium dodecyl sulfate-acrylamide gels; certain invariant features of the electrophoretic profiles, however, allowed clear differentiation between all the HSV-2 isolates and HSV-1.

Detection of a virus-specific antigen on the surface of herpes simplex virus-transformed cells

A virion-associated antigen, CP-1, was detected on the surface of hamster cells after transformation by inactivated herpes simplex virus type 1. Presence of the CP-1 antigen on the cells correlates with the synthesis of antibody by tumorbearing hamsters capable of neutralizing both herpes simplex virus types 1 and 2.

Studies of Marek's disease herpesvirus and turkey herpesvirus specific common antigen which stimulates the production of neutralizing antibodies

An agar-gel precipitation antigen prepared from the skin (feather-Ag) of chicken infected with JM strain of Marek's disease herpesvirus (MDHV) and cell extracts of cultures infected with either Type 2 plaque producing agent (PPA) of MDHV or turkey herpesvirus (HVT) (Type 2-Ag, HVT-Ag) had 1 precipitation line in common. Hyperimmune sera to the common antigen (common-Ag) neutralized to a greater extent by homologous antiserum. Absorption of HVT antiserum or hyperimmune serum to Type 2 PPA with common-Ag reduced their neutralizing activity. This reduction was almost complete with homologous antigen but less complete with heterologous antigen. The location of antigen in Type 2 PPA and HVT infected cells was determined using hyperimmune serum to the common-Ag in fluorescent antibody tests. Antigen mainly occurred in the cytoplasm of cells corresponding to the rounded refractile cells in the plaques, whereas unfixed cells showed antigen on the cytoplasmic membrane. The common-Ag associated with MDHV or HVT infections might be a virus structural component which is associated with the envelope.