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

Prediction and identification of potential immunodominant epitopes in glycoproteins B, C, E, G, and I of herpes simplex virus type 2

Twenty B candidate epitopes of glycoproteins B (gB2), C (gC2), E (gE2), G (gG2), and I (gI2) of herpes simplex virus type 2 (HSV-2) were predicted using DNAstar, Biosun, and Antheprot methods combined with the polynomial method. Subsequently, the biological functions of the peptides were tested via experiments in vitro. Among the 20 epitope peptides, 17 could react with the antisera to the corresponding parent proteins in the EIA tests. In particular, five peptides, namely, gB2_466–473 (EQDRKPRN), gC2_216–223 (GRTDRPSA), gE2_483–491 (DPPERPDSP), gG2_572–579 (EPPDDDDS), and gI2_286-295 (CRRRYRRPRG) had strong reaction with the antisera. All conjugates of the five peptides with the carrier protein BSA could stimulate mice into producing antibodies. The antisera to these peptides reacted strongly with the corresponding parent glycoproteins during the Western Blot tests, and the peptides reacted strongly with the antibodies against the parent glycoproteins during the EIA tests. The antisera against the five peptides could neutralize HSV-2 infection in vitro, which has not been reported until now. These results suggest that the immunodominant epitopes screened using software algorithms may be used for virus diagnosis and vaccine design against HSV-2.

Inner tegument protein pUL37 of herpes simplex virus type 1 is involved in directing capsids to the trans-Golgi network for envelopment

Secondary envelopment of herpes simplex virus type 1 has been demonstrated as taking place at the trans-Golgi network (TGN). The inner tegument proteins pUL36 and pUL37 and the envelope glycoproteins gD and gE are known to be important for secondary envelopment. We compared the cellular localizations of capsids from a virus mutant lacking the UL37 gene with those of a virus mutant lacking the genes encoding gD and gE. Although wild-type capsids accumulated at the TGN, capsids of the pUL37⁻ mutant were distributed throughout the cytoplasm and showed no association with TGN-derived vesicles. This was in contrast to capsids from a gD⁻gE⁻ mutant, which accumulated in the vicinity of TGN vesicles, but did not colocalize with them, suggesting that they were transported to the TGN but were unable to undergo envelopment. We conclude that the inner tegument protein pUL37 is required for directing capsids to the TGN, where secondary envelopment occurs.

Nuclear egress and envelopment of herpes simplex virus capsids analyzed with dual-color fluorescence HSV1(17+)

To analyze the assembly of herpes simplex virus type 1 (HSV1) by triple-label fluorescence microscopy, we generated a bacterial artificial chromosome (BAC) and inserted eukaryotic Cre recombinase, as well as beta-galactosidase expression cassettes. When the BAC pHSV1(17(+))blueLox was transfected back into eukaryotic cells, the Cre recombinase excised the BAC sequences, which had been flanked with loxP sites, from the viral genome, leading to HSV1(17(+))blueLox. We then tagged the capsid protein VP26 and the envelope protein glycoprotein D (gD) with fluorescent protein domains to obtain HSV1(17(+))blueLox-GFPVP26-gDRFP and -RFPVP26-gDGFP. All HSV1 BACs had variations in the a-sequences and lost the oriL but were fully infectious. The tagged proteins behaved as their corresponding wild type, and were incorporated into virions. Fluorescent gD first accumulated in cytoplasmic membranes but was later also detected in the endoplasmic reticulum and the plasma membrane. Initially, cytoplasmic capsids did not colocalize with viral glycoproteins, indicating that they were naked, cytosolic capsids. As the infection progressed, they were enveloped and colocalized with the viral membrane proteins. We then analyzed the subcellular distribution of capsids, envelope proteins, and nuclear pores during a synchronous infection. Although the nuclear pore network had changed in ca. 20% of the cells, an HSV1-induced reorganization of the nuclear pore architecture was not required for efficient nuclear egress of capsids. Our data are consistent with an HSV1 assembly model involving primary envelopment of nuclear capsids at the inner nuclear membrane and primary fusion to transfer capsids into the cytosol, followed by their secondary envelopment on cytoplasmic membranes.

Sialic acid on herpes simplex virus type 1 envelope glycoproteins is required for efficient infection of cells

Herpes simplex virus type 1 (HSV-1) envelope proteins are posttranslationally modified by the addition of sialic acids to the termini of the glycan side chains. Although gC, gD, and gH are sialylated, it is not known whether sialic acids on these envelope proteins are functionally important. Digestion of sucrose gradient purified virions for 4 h with neuraminidases that remove both alpha2,3 and alpha2,6 linked sialic acids reduced titers by 1,000-fold. Digestion with a alpha2,3-specific neuraminidase had no effect, suggesting that alpha2,6-linked sialic acids are required for infection. Lectins specific for either alpha2,3 or alpha2,6 linkages blocked attachment and infection to the same extent. In addition, the mobility of gH, gB, and gD in sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels was altered by digestion with either alpha2,3 specific neuraminidase or nonspecific neuraminidases, indicating the presence of both linkages on these proteins. The infectivity of a gC-1-null virus, DeltagC2-3, was reduced to the same extent as wild-type virus after neuraminidase digestion, and attachment was not altered. Neuraminidase digestion of virions resulted in reduced VP16 translocation to the nucleus, suggesting that the block occurred between attachment and entry. These results show for the first time that sialic acids on HSV-1 virions play an important role in infection and suggest that targeting virion sialic acids may be a valid antiviral drug development strategy.

Combinations of polyclonal or monoclonal antibodies to proteins of the outer membranes of the two infectious forms of vaccinia virus protect mice against a lethal respiratory challenge

Previous studies demonstrated that antibodies to live vaccinia virus infection are needed for optimal protection against orthopoxvirus infection. The present report is the first to compare the protective abilities of individual and combinations of specific polyclonal and monoclonal antibodies that target proteins of the intracellular (IMV) and extracellular (EV) forms of vaccinia virus. The antibodies were directed to one IMV membrane protein, L1, and to two outer EV membrane proteins, A33 and B5. In vitro studies showed that the antibodies to L1 neutralized IMV and that the antibodies to A33 and B5 prevented the spread of EV in liquid medium. Prophylactic administration of individual antibodies to BALB/c mice partially protected them against disease following intranasal challenge with lethal doses of vaccinia virus. Combinations of antibodies, particularly anti-L1 and -A33 or -L1 and -B5, provided enhanced protection when administered 1 day before or 2 days after challenge. Furthermore, the protection was superior to that achieved with pooled immune gamma globulin from human volunteers inoculated with live vaccinia virus. In addition, single injections of anti-L1 plus anti-A33 antibodies greatly delayed the deaths of severe combined immunodeficiency mice challenged with vaccinia virus. These studies suggest that antibodies to two or three viral membrane proteins optimally derived from the outer membranes of IMV and EV, may be beneficial for prophylaxis or therapy of orthopoxvirus infections.

Herpes simplex virus type 1 glycoprotein gC mediates immune evasion in vivo

Many microorganisms encode proteins that interact with molecules involved in host immunity; however, few of these molecules have been proven to promote immune evasion in vivo. Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC) binds complement component C3 and inhibits complement-mediated virus neutralization and lysis of infected cells in vitro. To investigate the importance of the interaction between gC and C3 in vivo, we studied the virulence of a gC-null strain in complement-intact and C3-deficient animals. Using a vaginal infection model in complement-intact guinea pigs, we showed that gC-null virus grows to lower titers and produces less severe vaginitis than wild-type or gC rescued virus, indicating a role for gC in virulence. To determine the importance of complement, studies were performed with C3-deficient guinea pigs; the results demonstrated significant increases in vaginal titers of gC-null virus, while wild-type and gC rescued viruses showed nonsignificant changes in titers. Similar findings were observed for mice where gC null virus produced significantly less disease than gC rescued virus at the skin inoculation site. Proof that C3 is important was provided by studies of C3 knockout mice, where disease scores of gC-null virus were significantly higher than in complement-intact mice. The results indicate that gC-null virus is approximately 100-fold (2 log10) less virulent that wild-type virus in animals and that gC-C3 interactions are involved in pathogenesis.

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.

Immunomodulatory effects of HSV2 glycoprotein D in HSV1 infected mice: implications for immunotherapy of recurrent HSV infection

Immunological analyses in this laboratory and others have suggested that a nonrecurrent HSV seropositive immune status is more closely correlated with a type 1 T helper cell (Th1) response characterized by elevated levels of interferon-gamma and IL2 rather than high titers of virus-specific antibodies. Effective intervention with an immunotherapeutic vaccine may require modulation of the regulatory network of T helper cells such that there is selective restimulation and expansion of the Th1 response. We have established a murine model for assessing the immunomodulatory capacity of an HSV glycoprotein subunit vaccine in animals with pre-existing herpes immunity. Animals were infected with varying doses of HSV1 and then administered glycoprotein D (gD) vaccine adjuvanted with aluminum phosphate at 3-week intervals. Observed changes in serological and cellular responses indicated that administration of subunit vaccine adjuvanted with aluminum phosphate could shift a dominant Th1 response, induced by sensitization with live HSV, towards a Th2 profile of activity. These data suggest that use of aluminum based adjuvants will not selectively stimulate Th1-associated responses and alternative adjuvants may be required for effective use of subunit vaccine in an immunotherapeutic indication in humans.

Immunization with recombinant varicella-zoster virus expressing herpes simplex virus type 2 glycoprotein D reduces the severity of genital herpes in guinea pigs

Varicella-zoster virus (VZV) is an attractive candidate for a live-virus vector for the delivery of foreign antigens. The Oka vaccine strain of VZV is safe and effective in humans, and recombinant Oka VZV (ROka) can be generated by transfecting cells with a set of overlapping cosmid DNAs. By this method, the herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) gene was inserted into an intergenic site in the unique short region of the Oka VZV genome. Expression of gD2 in cells infected with the recombinant Oka strain VZV (ROka-gD2) was confirmed by antibody staining of fixed cells and by immunoblot analysis. Immune electron microscopy demonstrated the presence of gD2 in the envelope of ROka-gD2 virions. The ability of ROka-gD2 to protect guinea pigs against HSV-2 challenge was assessed by inoculating animals with three doses of uninfected human fibroblasts, fibroblasts infected with ROka VZV, or fibroblasts infected with ROka-gD2. Neutralizing antibodies specific for HSV-2 developed in animals immunized with ROka-gD2. Forty days after the third inoculation, animals were challenged intravaginally with HSV-2. Inoculation of guinea pigs with ROka-gD2 significantly reduced the severity of primary HSV-2 infection (P < 0.001). These experiments demonstrate that the Oka strain of VZV can be used as a live virus vector to protect animals from disease with a heterologous virus.

Herpes simplex virus glycoprotein K is known to influence fusion of infected cells, yet is not on the cell surface

Syncytial mutants of herpes simplex virus (HSV) cause extensive fusion of cultured cells, whereas wild-type HSV primarily causes cell rounding and aggregation. A large fraction of syncytial viruses contain mutations in the UL53 gene, which encodes glycoprotein K (gK). Previously, we demonstrated that wild-type and syncytial forms of gK are expressed at similar levels and possess identical electrophoretic mobilities. Using immunofluorescence, we show that gK is not transported to the surfaces of cells infected with either wild-type or syncytial HSV. Instead, gK accumulates in the perinuclear and nuclear membranes of cells. This finding is in contrast to the behavior of all other HSV glycoproteins described to date, which reach the cell surface. When gK was expressed in the absence of other HSV proteins, using a recombinant adenovirus vector, a similar perinuclear and nuclear pattern was observed. In addition, gK remained sensitive to endoglycosidase H, consistent with the hypothesis that gK does not reach the Golgi apparatus and is retained in the endoplasmic reticulum and nuclear envelope. Therefore, although gK mutations promote fusion between the surface membranes of HSV-infected cells, the glycoprotein does not reach the plasma membrane and, thus, must influence fusion indirectly.

Baculovirus-expressed herpes simplex virus type 2 glycoprotein D is immunogenic and protective against lethal HSV challenge

Herpes simplex virus type 2 glycoprotein D (gD2) was cloned and expressed in the baculovirus-Spodoptera frugiperda system. Milligram quantities of glycoprotein were recovered from suspension culture and subjected to purification by ion-exchange and immunoaffinity chromatography. The resultant purified gD existed as a homogeneous 57,500 MW monomeric species demonstrating reactivity with anti-gD monoclonal antibodies including those directed at a non-sequential neutralizing epitope of gD. Immunization of Balb/c mice with doses of 0.1-10.0 micrograms of AlPO4-absorbed gD resulted in elicitation of humoral and cellular responses to both HSV1 and HSV2 as well as to purified gD1 and gD2. Immunized mice receiving an infectious dose of 1 x 10(6) p.f.u. of HSV2 via the footpad route were significantly protected against infection at all doses tested when compared with unimmunized AlPO4 and uninoculated control animals.

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.

Soluble glycoprotein D blocks herpes simplex virus type 1 infection of rat eyes

Herpes simplex virus type 1 (HSV-1) ocular infection in rats was blocked by treating the eyes with UV-inactivated virions containing glycoprotein D (gD) prior to ocular challenge. In contrast, rats treated with UV-inactivated virions lacking gD were not protected. A soluble, truncated form of HSV-2 gD (gD-2t) also protected against ocular infection. Treatment with gD-2t not only reduced mortality but also restricted progression of pathology and reduced the amount of viral antigen in the cornea. Host antibody or alpha/beta interferon responses to the gD-2t treatment were not detected. These results are similar to those observed in cell culture (D. C. Johnson, R. L. Burke, and T. Gregory, J. Virol. 64:2569-2576, 1990). The in vivo effect of exogenous gD is consistent with blocking of a cell surface gD receptor or with an inhibitory interaction of gD with virions.

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.

Effects of in vivo depletion of immunocyte populations on herpes simplex virus glycoprotein D vaccine-induced resistance to HSV2 challenge

BALB/c mice, preimmunized with a protective dose of native herpes simplex virus type 1 glycoprotein D (ngD1) vaccine, were depleted of selected immunocyte populations in vivo using monoclonal antibodies directed at Thy1+, L3T4+, or Lyt2+ cells. Following immunization and depletion, animals were inoculated with varied challenge levels of herpes simplex virus type 2 (HSV2) in the footpad and were monitored for disease. Both depleted undepleted gD-immunized mice were significantly protected when compared with placebo controls. T-cell-independent protection in Thy1 and L3T4-depleted ngD1-immunized animals was effective at low and moderate levels of HSV2 challenge levels, high levels of HSV2 giving high symptom scores in immunized and depleted mice. Depletion of Lyt2+ cells had no significant effect on the outcome of HSV2 infection. Depleted and nondepleted animals also were assessed in parallel for cellular and humoral responsiveness to ngD1 and to HSV antigens in vitro. Lymphoproliferative responses were abrogated in gD-immunized mice treated with anti-Thy1 or anti-L3T4, anti-Lyt2 treatment having little effect. Postimmunization T-cell depletion did not undermine ELISA or neutralizing antibody responses. These findings suggest that at low to moderate levels of virus challenge vaccine-elicited antibody plays a primary role in limiting the severity of infection, T-cell-mediated protective responses being of enhanced significance only at high levels of virus challenge.

Absence of asparagine-linked oligosaccharides from glycoprotein D of herpes simplex virus type 1 results in a structurally altered but biologically active protein

Glycoprotein D (gD) of herpes simplex virus contains three utilized sites (Asn-X-Ser/Thr) for addition of asparagine-linked carbohydrates (N-CHO). Previously, we used oligonucleotide-directed mutagenesis to alter serine or threonine residues to alanine at each N-CHO addition site. Studies with monoclonal antibodies showed that a mutant protein lacking all three sites (now designated AAA) was structurally altered because of the amino acid change at residue 96 as well as the absence of the N-CHO. In this study, we constructed additional single mutations at site 1 (residues 94 and 96) and found that in most cases, the amino acid change itself adversely affected the conformation of gD. However, changing asparagine 94 to glutamine (Q) at site 1 had the least effect on gD. We constructed a second triple mutant, QAA, which lacked all three N-CHO signals. The antigenic conformation of QAA was similar to that of gD produced in the presence of tunicamycin (TM-gD). However, binding of MAbs to the AAA protein or to single mutants altered at site 1 was reduced compared with TM-gD. Wild-type gD and QAA proteins were equally susceptible to digestion by trypsin or Staphylococcus aureus V8 protease. In contrast, the AAA protein was more sensitive to trypsin but less sensitive to V8, again suggesting conformational alterations of the AAA protein. Despite what appeared to be large changes in structure, each mutant complemented the infectivity of a virus lacking gD (F-gD beta). We conclude that the N-CHO and amino acids at N-CHO site 1 play an important role in forming and/or maintaining gD structure, but none of the N-CHO are required for gD to function in the complementation assay.

Characterization of a recombinant herpes simplex virus which expresses a glycoprotein D lacking asparagine-linked oligosaccharides

Glycoprotein D (gD) is an envelope component of herpes simplex virus essential for virus penetration. gD contains three sites for addition of asparagine-linked carbohydrates (N-CHO), all of which are utilized. Previously, we characterized mutant forms of herpes simplex virus type 1 gD (gD-1) lacking one or all three N-CHO addition sites. All of the mutants complemented the infectivity of a gD-minus virus, F-gD beta, to the same extent as wild-type gD. Here, we show that recombinant viruses containing mutations in the gD-1 gene which eliminate the three N-CHO signals are viable. Two such viruses, called F-gD(QAA)-1 and F-gD(QAA)-2, were independently isolated, and the three mutations in the gD gene in one of these viruses were verified by DNA sequencing. We also verified that the gD produced in cells infected by these viruses is devoid of N-CHO. Plaques formed by both mutants developed more slowly than those of the wild-type control virus, F-gD(WT), and were approximately one-half the size of the wild-type. One mutant, F-gD(QAA)-2, was selected for further study. The QAA mutant and wild-type gD proteins extracted from infected cells differed in structure, as determined by the binding of monoclonal antibodies to discontinuous epitopes. However, flow cytometry analysis showed that the amount and structure of gD found on infected cell surfaces was unaffected by the presence or absence of N-CHO. Other properties of F-gD(QAA)-2 were quite similar to those of F-gD(WT). These included (i) the kinetics of virus production as well as the intracellular and extracellular virus titers; (ii) the rate of virus entry into uninfected cells; (iii) the levels of gB, gC, gE, gH, and gI expressed by infected cells; and (iv) the turnover time of gD. Thus, the absence of N-CHO from gD-1 has some effect on its structure but very little effect on its function in virus infection in cell culture.

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.

Intracellular maturation and sorting of two herpes simplex virus type 1 glycoproteins. Immunogold staining of ultrathin cryosections

Simultaneous immunocytochemical triple staining of ultrathin cryosections of herpes simplex virus type 1-infected cells was carried out using monoclonal antibodies specific for glycoprotein C, glycoprotein D and alpha + beta tubulin. The viral glycoproteins were identified in the cytoplasm, in the Golgi sacs, on the plasma membrane and on the surface of intra- and extracellular virus particles, but not on the nuclear membrane. The glycoproteins identified in the cytoplasm outside the Golgi region were not always confined to the membranes of vesicles, but were often located in close proximity to the tubulin-labelled structures. The glycoproteins C and D were usually codistributed in the cytoplasm, and both accumulated in the Golgi sacs in the same membrane domains. As the glycoproteins occur in close proximity to the microtubular structures, we speculate that these might be directly involved in the intracellular transport of viral glycoproteins.

Native HSV glycoprotein D subunit vaccine: analysis of in vitro T-cell activation and antigen presentation

Native herpes simplex virus (HSV) glycoprotein D (ngD1) subunit vaccine, a potential human vaccine candidate, was examined to determine responsive murine lymphocyte populations in vitro. This vaccine preparation has been shown to protect against HSV challenge in mice and guinea pigs and to elicit humoral and cellular responses in rodents and primates. Immunized BALB/c mice were used in splenocyte lymphoproliferative studies to analyze the cellular response. After in vivo sensitization, the in vitro proliferative response observed appears to be resultant of Class II-restricted T-cell division in response to gD presented in the context of macrophage-expressed Ia.

Cysteine mutants of herpes simplex virus type 1 glycoprotein D exhibit temperature-sensitive properties in structure and function

We previously constructed seven mutations in the gene for glycoprotein D (gD) of herpes simplex virus type 1 in which the codon for one of the cysteine residues was replaced by a serine codon. Each of the mutant genes was cloned into a eucaryotic expression vector, and the proteins were transiently expressed in mammalian cells. We found that alteration of any of the first six cysteine residues had profound effects on protein conformation and oligosaccharide processing. In this report, we show that five of the mutant proteins exhibit temperature-sensitive differences in such properties as aggregation, antigenic conformation, oligosaccharide processing, and transport to the cell surface. Using a complementation assay, we have now assessed the ability of the mutant proteins to function in virus infection. This assay tests the ability of the mutant proteins expressed from transfected plasmids to rescue production of infectious virions of a gD-minus virus, F-gD beta, in Vero cells. Two mutant proteins, Cys-2 (Cys-106 to Ser) and Cys-4 (Cys-127 to Ser), were able to complement F-gD beta at 31.5 degrees C but not at 37 degrees C. The rescued viruses, designated F-gD beta(Cys-2) and F-gD beta(Cys-4), were neutralized as efficiently as wild-type virus by anti-gD monoclonal antibodies, indicating that gD was present in the virion envelope in a functional form. Both F-gD beta(Cys-2) and F-gD beta(Cys-4) functioned normally in a penetration assay. However, the infectivity of these viruses was markedly reduced compared with that of the wild type when they were preincubated at temperatures above 37 degrees C. The results suggest that mutations involving Cys-106 or Cys-127 in gD-1 confer a temperature-sensitive phenotype on herpes simplex virus. These and other properties of the cysteine-to-serine mutants allowed us to predict a disulfide bonding pattern for gD.

Escherichia coli-derived envelope protein gD but not gC antigens of herpes simplex virus protect mice against a lethal challenge with HSV-1 and HSV-2

Immunization studies with HSV-1 and HSV-2 envelope proteins expressed in Escherichia coli were performed. After active immunization of mice with a gD-1 antigen (Leu53-Ala312) expressed as a fusion protein, the animals were protected from a lethal challenge with HSV-1 and HSV-2. In addition, antisera from rabbits immunized with the same gD-1 antigen also conferred passive immunity to mice against a challenge infection with either HSV-1 or HSV-2. In contrast to these successful gD-1 protection experiments, various gC-1 and gC-2 fusion proteins from E. coli failed to induce protective immunity. Moreover, the mice sera from immunized animals were not able to react with the authentic, glycosylated gC-1 and gC-2 envelope proteins, whereas sera raised against authentic gC-1 and gC-2 glycoproteins do recognize the gC fusion proteins from E. coli. These results indicate, that E. coli might represent an ideal system for expressing gD antigens as a possible component of a HSV vaccine, whereas gC antigen cannot be produced in an immunocompetent form in E. coli.

Intratypic variation of herpes simplex virus type 2 isolates detected by monoclonal antibodies against viral glycoproteins

Monoclonal antibodies (MAbs) to herpes simplex virus (HSV) glycoproteins gD, gG, gB, and gE were used to analyze antigenic variations of 128 genital HSV-2 isolates by an indirect enzyme-linked immunosorbent assay (ELISA). Isolates were considered significantly different from the standard HSV-2 strain 186 when their optical density (OD) in ELISA was less than half that of strain 186. This criterion gave 30 patterns of reactivity among the genital HSV-2 isolates. The MAbs to gB, gG, and 2 of the gD antibodies reacted with more than 90% of the isolates, suggesting that these MAbs recognized highly conserved epitopes. However, the gE MAb reacted with only 47% of the isolates, and one of the gD antibodies with only 39%. Thus, HSV-2 can readily tolerate modifications in some parts of the gD and gE molecules while remaining infectious.

Influence of asparagine-linked oligosaccharides on antigenicity, processing, and cell surface expression of herpes simplex virus type 1 glycoprotein D

Glycoprotein D (gD) is an envelope component of herpes simplex virus types 1 and 2. gD-1 contains three sites for the addition of N-linked carbohydrate (N-CHO), all of which are used. Three mutants were constructed by site-directed mutagenesis, each of which altered one N-CHO addition site from Asn-X-Thr/Ser to Asn-X-Ala. A fourth mutant was altered at all three sites. The mutant genes were inserted into an expression vector, and the expressed protein was analyzed in transiently transfected COS-1 cells. The mutant protein lacking N-CHO at site 1 (Asn-94) had a reduced affinity for monoclonal antibodies (MAbs) to discontinuous epitopes, suggesting that the conformation of the protein had been altered. However, the protein was processed and transported to the cell surface. The absence of N-CHO at site 2 (Asn-121) had no apparent effect on processing or transport of gD-1 but resulted in reduced binding of two MAbs previously shown to be in group VI. Binding of other MAbs to discontinuous epitopes (including other group VI MAbs) was not affected. The absence of N-CHO at site 3 (Asn-262) had no effect on processing, transport, or conformation of the gD-1 protein. The absence of N-CHO from site 1 or from all three sites resulted in the formation of high-molecular-weight aggregates or complexes and a reduction in MAb binding. However, these proteins were modified by the addition of O-glycans and transported to the cell surface. We conclude that the absence of the first or all N-linked carbohydrates alters the native conformation of gD-1 but does not prevent its transport to the cell surface.

Neutralizing antibodies specific for glycoprotein H of herpes simplex virus permit viral attachment to cells but prevent penetration

Monoclonal antibodies specific for gH of herpes simplex virus were shown previously to neutralize viral infectivity. Results presented here demonstrate that these antibodies (at least three of them) block viral penetration without inhibiting adsorption of virus to cells. Penetration of herpes simplex virus is by fusion of the virion envelope with the plasma membrane of a susceptible cell. Electron microscopy of thin sections of cells exposed to virus revealed that neutralized virus bound to the cell surface but did not fuse with the plasma membrane. Quantitation of virus adsorption by measuring the binding of purified radiolabeled virus to cells revealed that the anti-gH antibodies had little or no effect on adsorption. Monitoring cell and viral protein synthesis after exposure of cells to infectious and neutralized virus gave results consistent with the electron microscopic finding that the anti-gH antibodies blocked viral penetration. On the basis of the results presented here and other information published elsewhere, it is suggested that gH is one of three glycoproteins essential for penetration of herpes simplex virus into cells.

Fine mapping of antigenic site II of herpes simplex virus glycoprotein D

Glycoprotein D (gD) is a virion envelope component of herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) which plays an important role in viral infection and pathogenesis. Previously, anti-gD monoclonal antibodies (MAbs) were arranged into groups which recognize distinct type-common and type-specific sites on HSV-1 gD (gD-1) and HSV-2 gD (gD-2). Several groups recognize discontinuous epitopes which are dependent on tertiary structure. Three groups, VII, II, and V, recognize continuous epitopes present in both native and denatured gD. Previously, group II consisted of a single MAb, DL6, whose epitope was localized between amino acids 268 and 287. In the study reported here, we extended our analysis of the antigenic structure of gD, concentrating on continuous epitopes. The DL6 epitope was localized with greater precision to residues 272 to 279. Four additional MAbs including BD78 were identified, each of which recognizes an epitope within residues 264 to 275. BD78 and DL6 blocked each other in binding to gD. In addition, a mutant form of gD was constructed in which the proline at 273 was replaced by serine. This change removes a predicted beta turn in gD. Neither antibody reacted with this mutant, indicating that the BD78 and DL6 epitopes overlap and constitute an antigenic site (site II) within residues 264 to 279. A separate antigenic site (site XI) was recognized by MAb BD66 (residues 284 to 301). This site was only six amino acids downstream of site II, but was distinct as demonstrated by blocking studies. Synthetic peptides mimicking these and other regions of gD were screened with polyclonal antisera to native gD-1 or gD-2. The results indicate that sites II, V, VII, and XI, as well as the carboxy terminus, are the major continuous antigenic determinants on gD. In addition, the results show that the region from residues 264 through 369, except the transmembrane anchor, contains a series of continuous epitopes.

Herpes simplex virus glycoprotein D is sufficient to induce spontaneous pH-independent fusion in a cell line that constitutively expresses the glycoprotein

Spontaneous small polykaryocytes were detected in a cell line designated BJ-o that harbors the BamHI J fragment of herpes simplex virus 1 DNA and expresses constitutively glycoprotein D (gD). The fusion activity of BJ-o cells correlated with gD production and was drastically reduced following exposure of the cells to monoclonal antibody HD1 to gD. Studies on the characteristics and requirements of cell fusion dependent on gD led to the conclusion that the characteristics and requirements for gD-mediated fusion activity of BJ-o cells are similar to those previously reported for cell fusion induced by the virus in that (i) polykaryocytosis was not augmented by exposure to medium of low pH with or without prior exposure to trypsin, (ii) the number of polykaryocytes was reduced following removal of terminal sialic acid residues by neuraminidase, and (iii) the number of polykaryocytes was augmented by masking of high-mannose N-linked oligosaccharides with concanavalin A or with its reduced form, succinyl concanavalin A. This effect was reversed by competition with mannose.

Antigenic analysis of a major neutralization site of herpes simplex virus glycoprotein D, using deletion mutants and monoclonal antibody-resistant mutants

Herpes simplex virus glycoprotein D is a component of the virion envelope and appears to be involved in attachment, penetration, and cell fusion. Monoclonal antibodies against this protein can be arranged in groups on the basis of a number of biological and biochemical properties. Group I antibodies are type common, have high complement-independent neutralization titers, and recognize discontinuous (conformational) epitopes; they are currently being used in several laboratories to study the functions of glycoprotein D. We have used a panel of neutralization-resistant mutants to examine the relationships between these antibodies in detail. We found that they can be divided into two subgroups, Ia and Ib, such that mutations selected with Ia antibodies have little or no effect on binding and neutralization by Ib antibodies and vice versa. In addition, Ia antibodies are able to bind deletion and truncation mutants of glycoprotein D that Ib antibodies do not recognize, suggesting that their epitopes are physically distinct. However, with one exception, Ia and Ib antibodies block each other strongly in binding assays with purified glycoprotein D, whereas antibodies from other groups have no effect. We have therefore defined the sum of the Ia and Ib epitopes as antigenic site 1.

Immunological properties of an N-terminal fragment of herpes simplex virus type 1 glycoprotein D expressed in Escherichia coli

The N-terminal fragment, comprising residues -5 to 55 of herpes simplex virus type 1 glycoprotein D was expressed as a beta-galactosidase fusion protein in Escherichia coli. This gD-fusion protein reacts with monoclonal antibody LP 14 directed against glycoprotein D of HSV. Antisera obtained after immunization of rabbits with purified gD-fusion protein react with HSV-1 gD in a Western blot and with N-terminal synthetic peptides of gD. In addition, these antisera are able to neutralize viral infectivity in vitro.

Expression of herpes simplex virus type 1 glycoprotein D deletion mutants in mammalian cells

Glycoprotein D (gD) is a viron envelope component of herpes simplex virus types 1 and 2. We have previously defined seven monoclonal antibody (MAb) groups which recognize distinct epitopes on the mature gD-1 protein of 369 amino acids. MAb groups VII, II, and V recognize continuous epitopes at residues 11-19, 272-279, and 340-356, respectively. MAb groups I, III, IV, and VI recognize discontinuous epitopes. Recent studies have focused on epitopes I, III, and VI. Using truncated forms of gD generated by recombinant DNA methods and proteolysis, epitopes III, IV, and VI were located within amino acids 1-233. A portion of discontinuous epitope I was located in a region within residues 233-275. For this study, we used recombinant DNA methods to create mutations in the gD-1 gene and studied the effects of those mutations on gD as expressed in mammalian cells. Plasmid pRE4, containing the coding sequence of gD-1 and the Rous sarcoma virus long terminal repeat promoter, was transfected into mammalian cells. The expressed protein, gD-1-(pRE4), was identical in size and antigenic properties to gD-1 from infected cells. Six in-frame deletion mutations were subsequently constructed by using restriction enzymes to excise portions of the gD-1 gene. Plasmids carrying these mutated forms were transfected into cells, and the corresponding proteins were examined at 48 h posttransfection for antigenicity and glycosylation patterns. Three deletions of varying size were located downstream of residue 233. Analysis of these mutants showed that amino acids within the region 234-244 were critical for binding of DL11 (group I), but not for other MAb groups. Three other deletion mutants lost all ability to bind MAbs which recognize discontinuous epitopes. In addition, much of the gD expressed by these mutants was observed to migrate as high-molecular-weight aggregated forms in nondenaturing gels. Each of these mutations involved the loss of a cysteine residue, suggesting that disulfide linkages play an essential role in the formation of discontinuous epitopes. The extent of glycosylation of the mutant gD molecules accumulated at 48 h posttransfection suggested altered carbohydrate processing. In one case, there was evidence for increased O-linked glycosylation. Those proteins which had lost a cysteine residue as part of the deletion did not accumulate molecules processed beyond the high-mannose stage. The results suggest that carbohydrate processing during synthesis of gD is very sensitive to alterations in structure, particularly changes involving cysteine residues.

A multigene family encodes the human cytomegalovirus glycoprotein complex gcII (gp47-52 complex)

The HXLF (HindIII-X left reading frame) gene family is a group of five genes that share one or two regions of homology and are arranged in tandem within the short unique component of the human cytomegalovirus genome (K. Weston and B.G. Barrell, J. Mol. Biol. 192:177-208, 1986). These genes were cloned into an SP6 expression vector in both the sense and antisense orientations. An abundant 1.62-kilobase (kb) bicistronic mRNA, predicted to originate from HXLF1 and HXLF2, was detected in the cytoplasm of infected human fibroblast cells by Northern (RNA) blot analysis. Less abundant RNAs of 1.0 and 0.8 kb, predicted to originate from the HXLF5 and HXLF2 genes, respectively, were also detected. Monocistronic, bicistronic, and polycistronic RNAs synthesized in vitro by using SP6 polymerase were translated in rabbit reticulocyte lysates with or without canine pancreatic microsomal membranes. The HXLF1 or the HXLF1 and HXLF2 translation products were detected when the above mRNAs were used. The HXLF3, HXLF4, and HXLF5 gene products were not detected by in vitro translation of the SP6-derived polycistronic mRNA. Nonglycosylated or glycosylated HXLF1 and HXLF2 gene products were immunoprecipitated by monoclonal antibody 9E10, which is specific for a virion envelope glycoprotein complex designated gcII (gp47-52 complex). In addition, the monoclonal antibody 9E10 immunoprecipitated a diffuse glycoprotein band, designated gp47-52, from HCMV-infected cell lysates. The amino acid composition of gp47-52 purified from viron envelopes has the highest similarity to the predicted amino acid composition of the HXLF1 plus HXLF2 open reading frames, but it is more similar to HXLF2 than to HXLF1. The Northern blot results imply that gp47-52 is synthesized predominantly from the abundant 1.62-kb bicistronic mRNA encoded by the HXLF1 and HXLF2 genes. However, the glycoprotein could also be synthesized by the monocistronic 0.8-kb mRNA encoded by the HXLF2 gene as well as by the mRNAs predicted from the other HXLF genes.

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.

Evaluation of pseudorabies virus glycoprotein gp50 as a vaccine for Aujeszky's disease in mice and swine: expression by vaccinia virus and Chinese hamster ovary cells

Pseudorabies virus (PRV) is an alphaherpesvirus which causes an economically important disease of swine. One of the PRV glycoproteins, gp50, was previously identified as the sequence homolog of herpes simplex virus glycoprotein gD (E.A. Petrovskis, J.G. Timmins, M.A. Armentrout, C.C. Marchioli, R.J. Yancey, Jr., and L.E. Post, J. Virol. 59:216-223, 1986). gp50 was evaluated as a PRV subunit vaccine candidate. gp50 protected mice from PRV-induced mortality either when delivered via infection with a recombinant vaccinia virus or when administered as a subunit vaccine produced in a eucaryotic cell line, Chinese hamster ovary (CHO) cells. In addition, gp50 synthesized in CHO cells protected pigs from lethal infection with PRV. This result demonstrates that a single viral glycoprotein could induce a protective immune response in the natural host of a herpesvirus infection.

Neutralizing monoclonal antibodies specific for herpes simplex virus glycoprotein D inhibit virus penetration

Nine monoclonal antibodies specific for glycoprotein D (gD) of herpes simplex virus type 1 were selected for their ability to neutralize virus in the presence of complement. Four of these antibodies exhibited significant neutralization titers in the absence of complement, suggesting that their epitope specificities are localized to site(s) which contribute to the role of gD in virus infectivity. Each of these antibodies was shown to effectively neutralize virus after virion adsorption to cell surfaces, indicating that neutralization did not involve inhibition of virus attachment. Although some of the monoclonal antibodies partially inhibited adsorption of radiolabeled virions, this effect was only observed at concentrations much higher than that required to neutralize virus and did not correlate with complement-independent virus-neutralizing activity. All of the monoclonal antibodies slowed the rate at which virus entered cells, further suggesting that antibody binding of gD inhibits virus penetration. Experiments were carried out to determine the number of different epitopes recognized by the panel of monoclonal antibodies and to identify epitopes involved in complement-independent virus neutralization. Monoclonal antibody-resistant (mar) mutants were selected by escape from neutralization with individual gD-specific monoclonal antibodies. The reactivity patterns of the mutants and antibodies were then used to construct an operational antigenic map for gD. This analysis identified a minimum of six epitopes on gD that could be grouped into four antigenic sites. Antibodies recognizing four distinct epitopes contained in three antigenic sites were found to neutralize virus in a complement-independent fashion. Moreover, mar mutations in these sites did not affect the processing of gD, rate of virus penetration, or the ability of the virus to replicate at high temperature (39 degrees C). Taken together, these results (i) confirm that gD is a major target antigen for neutralizing antibody, (ii) indicate that the mechanism of neutralization can involve inhibition of virus penetration of the cell surface membrane, and (iii) strongly suggest that gD plays a direct role in the virus entry process.

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.

Prospects for the clinical management of human cytomegalovirus infections

Infection of susceptible populations by human cytomegalovirus (HCMV) is a significant public health problem in Western societies. Vaccination with live attenuated strains of HCMV has demonstrated some degree of clinical benefit but objections based on the possibility of these viruses becoming latent and their potential oncogenicity must be considered. Our knowledge of the biology and immunology of HCMV, although advancing rapidly, is still a long way short of being able to predict candidate subunit vaccines based on virus encoded proteins or glycoproteins. Treatment of the disease by injection of antibodies awaits a breakthrough and chemicals effective in the control of other human herpes viruses are disappointingly ineffective against HCMV. Clearly, prophylaxis is preferable to therapy and it is in the design of new effective vaccines that endeavours must be channelled so that we can control complications associated with severe clinical infection with this virus.

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.

A murine monoclonal antibody recognising a single glycoprotein within a human cytomegalovirus virion envelope glycoprotein complex

Nonionic detergent solubilised polypeptides from highly purified human cytomegalovirus virions were used as immunogens to produce murine monoclonal antibody secreting hybridomas. One monoclonal antibody was shown, by immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), to precipitate three glycoproteins with molecular weights 52, 95, and 130 (all X 10(3)) and one minor component with a molecular weight of 50 X 10(3). When virion envelope components were first separated by SDS-PAGE and electrophoretically transferred to nitrocellulose membranes, this monoclonal antibody recognised two related components with molecular weights 50 and 52 (both X 10(3)). Immunofluorescence studies suggested that these viral antigens were associated with membrane systems of virus-infected cells and were particularly abundant late in infection.

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.

Specificities of monoclonal and polyclonal antibodies that inhibit adsorption of herpes simplex virus to cells and lack of inhibition by potent neutralizing antibodies

Polyclonal and monoclonal antibodies to individual herpes simplex virus (HSV) glycoproteins were tested for ability to inhibit adsorption of radiolabeled HSV type 1 (HSV-1) strain HFEMsyn [HSV-1(HFEM)syn] to HEp-2 cell monolayers. Polyclonal rabbit antibodies specific for glycoprotein D (gD) or gC and three monoclonal mouse antibodies specific for gD-1 or gC-1 most effectively inhibited HSV-1 adsorption. Antibodies of other specificities had less or no inhibitory activity despite demonstrable binding of the antibodies to virions. Nonimmune rabbit immunoglobulin G and Fc fragments partially inhibited adsorption when used at relatively high concentrations. These results suggest involvement of gD, gC, and perhaps gE (the Fc-binding glycoprotein) in adsorption. The monoclonal anti-gD antibodies that were most effective at inhibiting HSV-1 adsorption had only weak neutralizing activity. The most potent anti-gD neutralizing antibodies had little effect on adsorption at concentrations significantly higher than those required for neutralization. This suggests that, although some anti-gD antibodies can neutralize virus by blocking adsorption, a more important mechanism of neutralization by anti-gD antibodies may be interference with a step subsequent to adsorption, possibly penetration.

The immune response to herpes simplex virus: comparison of the specificity and relative titers of serum antibodies directed against viral polypeptides following primary herpes simplex virus type 1 infections

Employing an immunoblotting technique, the polypeptide specificity and relative titers of anti-HSV IgG reactive with denaturation-resistant epitopes on HSV proteins were determined in patients experiencing primary HSV-1 infections at various anatomical sites. Early sera from previously seronegative patients with primary HSV-1 infections were found to have comparatively low levels of antibody directed against the major viral glycoprotein antigens (gB, gC, and gD) relative to titers present in sera of individuals with long-standing, latent orofacial HSV-1 infections. Patients with primary infections did however have high titers of antibody directed against a series of low molecular weight HSV polypeptide antigens. These antigens were found to be antigenically related to a structural component of virion nucleocapsids. At later times postinfection, titers of antibodies directed against other viral polypeptides including the major glycoproteins increased to levels more closely approximating those observed in latently infected individuals. These results indicate that the anti-HSV IgG detected by immunoblot analysis which appears earliest following primary infection is not directed against the known major infected cell or virion glycoprotein surface antigens but rather against an internal capsid protein of HSV.

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.