Specificity of human natural killer cells in limiting dilution culture for determinants of herpes simplex virus type 1 glycoproteins

Molecular Basis for the Recognition of Herpes Simplex Virus Type 1 Infection by Human Natural Killer Cells

Primary infection with Herpes simplex virus type 1 (HSV1) is subclinical or only mildly symptomatic in normal individuals, yet the reason for the body's effective immune defense against this pathogen in the absence of antigen-specific immunity has not been well understood. It is clear that human natural killer (NK) cells recognize and kill HSV1-infected cells, and those individuals who either lack or have functionally impaired NK cells can suffer severe, recurrent, and sometimes fatal HSV1 infection. In this article, we review what is known about the recognition of HSV1 by NK cells, and describe a novel mechanism of innate immune surveillance against certain viral pathogens by NK cells called Fc-bridged cell-mediated cytotoxicity.

Cyclophosphamide enhances glioma virotherapy by inhibiting innate immune responses

Clinical trials are testing oncolytic viruses (OVs) as therapies for cancer. We have shown that animals that have brain tumors and are treated with a herpes simplex virus (HSV)-derived OV live significantly longer when cyclophosphamide (CPA) is preadministered. Here, we explore the mechanisms behind this finding. In a syngeneic rat glioma model, intratumoral HSV administration is associated with rapid increase of natural killer cells, microglia/macrophages (CD68+ and CD163+), and IFN-gamma. Pretreatment with CPA enhances HSV replication and oncolysis and reduces an HSV-mediated increase in CD68+ and CD163+ cells and intratumoral IFN-gamma. Molecular imaging shows CPA pretreatment to inhibit HSV-induced infiltration of tumor-associated phagocytic cells. Our results reveal molecular and cellular mechanisms that inhibit intratumoral spread of HSV and suggest a therapeutic path for improving the efficacy of virotherapy as a treatment for cancer.

The immune response to ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is a prevalent microbial pathogen infecting 60% to 90% of the adult world population. The co-evolution of the virus with humans is due, in part, to adaptations that the virus has evolved to aid it in escaping immune surveillance, including the establishment of a latent infection in its human host. A latent infection allows the virus to remain in the host without inducing tissue pathology or eliciting an immune response. During the acute infection or reactivation of latent virus, the immune response is significant, which can ultimately result in corneal blindness or fatal sporadic encephalitis. In fact, HSV-1 is one of the leading causes of infectious corneal blindness in the world as a result of chronic episodes of viral reactivation leading to stromal keratitis and scarring. Significant inroads have been made in identifying key immune mediators that control ocular HSV-1 infection and potentially viral reactivation. Likewise, viral mechanisms associated with immune evasion have also been identified and will be discussed. Lastly, novel therapeutic strategies that are currently under development show promise and will be included in this review. Most investigators have taken full advantage of the murine host as a viable working in vivo model of HSV-1 due to the sensitivity and susceptibility to viral infection, ease of manipulation, and a multitude of developed probes to study changes at the cellular and molecular levels. Therefore, comments in this review will primarily be restricted to those observations pertaining to the mouse model and the assumption (however great) that similar events occur in the human condition.

Expression and characterization of baculovirus expressed herpes simplex virus type 1 glycoprotein L

We have constructed a recombinant baculovirus expressing high levels of the herpes simplex virus type 1 (HSV-1) glycoprotein L (gL) in Sf9 cells. Sf9 cells infected with this recombinant virus synthesized three polypeptides of 26-27 kDa 28 kDa, and 31 kDa. The 28 and 31 kDa species were sensitive to tunicamycin and N-glycosidase F (PNGase F) treatment, suggesting that they were glycosylated. As shown by both indirect immunofluorescence and Western blot analysis, using polyclonal antibodies to synthetic gL peptides indicated that the baculovirus expressed gL was abundant on the surface of baculovirus gL infected Sf9 cells. A small fraction of the 31 kDa polypeptide was secreted into the extracellular medium as judged by Western blot analysis. The secreted form of gL was completely resistant to Endoglycosidase H (Endo-H), while the membrane associated form of gL was only partially resistant to Endo-H treatment, suggesting that the secreted gL represented a subpopulation of the membrane bound gL. Mice vaccinated with baculovirus expressed gL produced serum antibodies that reacted with authentic HSV-1 gL. However, these mice produced no HSV-1 neutralizing antibody (titer < 1:10) and they were not protected from lethal intraperitoneal or lethal ocular challenge with HSV-1. Thus, when used as a vaccine in the mouse model, gL, similar to our findings with HSV-1 gH, but unlike our results with the other 6 HSV-1 glycoproteins that we have expressed in this baculovirus system, did not provide any protection against HSV-1 challenge.

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

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

Heterogeneity amongst natural killer cells revealed by limiting dilution culture; selectivity against virus-infected and tumour cell targets

Previous studies have suggested that natural killer (NK) cells exhibit heterogeneous cytotoxicity towards different tumour cell targets. No studies have set out to determine whether different NK populations have relative selectivity for virus-infected cells. The aims of this study were to determine if this was the case for short-term clones, and whether there were differences in relative selectivity for particular target cells between clones with NK activity but with different surface phenotypes. Cells from different starting populations [whole peripheral blood lymphocytes (PBL), E-rosette positive or negative, CD16+ or CD3- cells] were grown in limiting dilution culture (LDC) with interleukin-2 (IL-2). The precursor frequency (NK-p) of cells proliferating and exhibiting NK activity towards various virus-infected or uninfected fibroblasts or tumour cell targets was determined by split-well analysis of the LDC. The relative NK-p were similar for different individuals, but were much lower for virus-infected fibroblasts than a tumour cell target. The pattern of cytotoxicity of 757 short-term clones, identified from the LDC, against four to five tumour and virus-infected target cells were analysed. We conclude that there was selective lysis of virus-infected cells by a proportion of NK clones which were predominantly PBL-derived (mainly CD3+). Twenty-six per cent of E(+)-derived clones lysed Molt4 cells only in the absence of phytohaemagglutinin (PHA), and a proportion of PBL- or E(+)-derived clones (up to 44%) lysed uninfected or virus-infected fibroblasts but not Molt4+PHA. Thus, under hese conditions lectin-induced cytotoxicity does not detect total potential cytotoxicity.

Expression of the Marek's disease virus (MDV) homolog of glycoprotein B of herpes simplex virus by a recombinant baculovirus and its identification as the B antigen (gp100, gp60, gp49) of MDV

A gene encoding a homolog of glycoprotein B of herpes simplex virus (gB homolog) has been identified on the Marek's disease virus (MDV) genome (L. J. N. Ross, M. Sanderson, S. D. Scott, M. M. Binns, T. Doel, and B. Milne, J. Gen. Virol. 70:1789-1804, 1989); however, the molecular and immunological characteristics of the gene product(s) are still not clear. In the present study, the gB homolog of MDV was expressed in insect cells by a recombinant baculovirus, and it was characterized to determine its molecular and antigenic properties. The expressed recombinant protein had three molecular sizes (88 to 110, 58, and 49 kDa) and was recognized by antisera from chickens inoculated with each of the three serotypes of MDV. By immunofluorescence analysis, it was shown that the protein was expressed in the cytoplasm and on the surface of the recombinant baculovirus-infected cells. The gB homolog of MDV was processed similarly to pseudorabies virus and varicella-zoster virus with respect to cleavage and the intramolecular disulfide bond between the cleaved products. Interestingly, the expressed protein reacted with monoclonal antibody M51, specific to the B antigen (gp100, gp60, gp49) of MDV, although the locations of the gene encoding the B antigen and of the gene encoding the gB homolog were reported to be different. Moreover, competitive experiments revealed that anti-gB homolog serum and monoclonal antibody M51 recognized the same molecules. From these results, the gB homolog and the B antigen of MDV seem to be the same glycoprotein.

A comparison of T cell responses to glycoprotein B (gB-1) of herpes simplex virus type 1 and its non-glycosylated precursor protein, pgB-1

The ability of non-glycosylated precursor glycoprotein B (pgB) to induce T cell responses in herpes simplex virus (HSV) infected mice was compared with fully glycosylated glycoprotein B (gB) and with whole virus. pgB was as effective as gB in priming for virus- and glycoprotein-specific T cells. pgB could also re-stimulate virus or glycoprotein primed cells in vitro as efficiently as gB. In addition, priming with pgB protected mice against a lethal challenge with HSV type 1 (HSV-1) and could induce the early in vivo production of IL-2 and IL-3 in infected mice. In all of these responses, pgB was as effective as gB. Thus, the carbohydrate side chains on gB do not appear to be necessary for T cell recognition of this protein.

Immediate-early gene expression is sufficient for induction of natural killer cell-mediated lysis of herpes simplex virus type 1-infected fibroblasts

Herpes simplex virus type 1 (HSV-1)-infected human fibroblast (HSV-FS) targets are susceptible to lysis by natural killer (NK) cells, whereas uninfected FS are resistant to lysis. Studies were undertaken to determine the mechanism of this preferential susceptibility. HSV-FS were not intrinsically less stable than FS, as determined by a 51Cr release assay under hypotonic shock in the presence of rat granule cytolysin and by sensitivity to anti-human leukocyte antigen class I antibody plus complement. Single-cell assays in agarose demonstrated that although similar numbers of large granular lymphocytes bound to the HSV-FS and FS targets, the conjugates with HSV-FS were lysed at a much higher frequency than those with FS. These results suggested that both targets are bound by the NK cells but only the HSV-FS were able to trigger lysis. The requirement for active virus expression was demonstrated by failure of emetine-treated HSV-FS targets or targets infected with UV-inactivated HSV to be lysed by NK effectors. To evaluate the role of viral glycoproteins in conferring susceptibility to lysis, Fab were prepared from HSV-1-seropositive sera; these Fab were unable to block lysis of the HSV-FS. Furthermore, incubation in phosphonoacetic acid failed to reduce NK(HSV-FS) activity despite sharp reductions in viral glycoprotein synthesis. Finally, targets infected with tsLB2 at the nonpermissive temperature were lysed as well as or better than targets infected with wild-type virus, indicating that HSV immediate-early gene product expression is sufficient for conferring susceptibility to lysis. We conclude that expression of nonstructural viral proteins or virally induced cellular gene products early in the course of infection rather than structural glycoproteins is required for NK lysis of HSV-FS targets.

Sequence analysis of a glycoprotein D gene homolog within the unique short segment of the EHV-1 genome

DNA sequence analysis of one-third of the unique short (Us) segment of the equine herpesvirus type 1 (EHV-1) genome revealed an open reading frame (ORF) whose translated sequence exhibits significant homology to glycoprotein D of herpes simplex virus (HSV) types 1 and 2 and to pseudorabies virus (PRV) glycoprotein 50, the gD equivalent. The ORF of the EHV-1 gD homolog lies within the pSZ-4 BamHI/KpnI fragment (map units 0.865 to 0.872 and 0.869 to 0.884) and is capable of encoding a polypeptide of 385 amino acids (43,206 molecular weight). Analysis of the nucleotide sequence revealed a complete transcriptional unit including CAAT and TATA elements and signals for polyadenylation. The predicted protein exhibits features typical of a transmembrane protein: a hydrophobic N-terminal signal sequence followed by a probable cleavage site, four potential N-linked glycosylation sites, and a hydrophobic membrane-spanning domain near the carboxyl terminus followed by a charged membrane anchor sequence.

Bovine naturally cytolytic cell activation against bovine herpes virus type 1-infected cells does not require late viral glycoproteins

Freshly isolated or overnight cultured bovine peripheral blood mononuclear (PBM) cells lysed bovine herpes virus 1 (BHV-1)-infected allogeneic and xenogeneic target cells but not non-infected target cells. To determine if late viral genes contribute to target cell lysis, phosphonoacetic acid (PAA), an inhibitor of DNA polymerase activity, was used to block DNA replication that is required for expression of late viral proteins. Both adherent and non-adherent (NA) cell populations mediated lysis against PAA-treated BHV-1-infected target cells in both 4- and 20-hr assays, indicating recognition and killing occurred in the absence of expression of late BHV-1 glycoproteins. Thus recognition of BHV-1 by bovine natural cytolytic effector cells does not require recognition of late BHV-1 glycoproteins for killing virally infected target cells.

Functional cross-reactivity between the glycoprotein B of herpes simplex virus type 1 and Epstein-Barr virus

A monoclonal antibody (T157) directed against gB-1, the glycoprotein B (gB) of herpes simplex virus-1 (HSV-1) shows positive indirect immunoflourescent staining with an Epstein-Barr virus (EBV)-transformed lymphoblastoid cell line B95-8. SDS PAGE and Western blot analysis show that B95-8 cells contain a 110,000 MW protein that co-migrates with the 110,000-115,000 MW gB-1. The gB-1 homologue of EBV (gB-EBV), immunopurified using a T157 affinity column, cross-stimulates HSV-1 immune T cells to proliferate in vitro. Mice immunized by a single subcutaneous injection of 30 microg gB-EBV in saline developed significant protection against HSV-1 challenge infection. Therefore gB-EBV can be considered a potential candidate vaccine and as an antigen to examine the cell-mediated immune response mounted by the host to limit virus spread during productive infection. The significance of a better understanding of the immune response to this and other EBV proteins of productive infection as an alternative to limit tumour growth by preventing virus spread is discussed.

Monoclonal antibodies define a domain on herpes simplex virus glycoprotein B involved in virus penetration

In an earlier report (S.D. Marlin, S.L. Highlander, T.C. Holland, M. Levine, and J.C. Glorioso, J. Virol. 59: 142-153), we described the production and use of complement-dependent virus-neutralizing monoclonal antibodies (MAbs) and MAb-resistant (mar) mutants to identify five antigenic sites (I to V) on herpes simplex virus type 1 glycoprotein B (gB). In the present study, the mechanism of virus neutralization was determined for a MAb specific for site III (B4), the only site recognized by MAbs which exhibited complement-independent virus-neutralizing ability. This antibody had no detectable effect on virus attachment but neutralized viruses after adsorption to cell monolayers. These findings implied that the mechanism of B4 neutralization involved blocking of virus penetration. The remaining antibodies, which recognized sites I, II, and IV, required active complement for effective neutralization. These were further studied for their ability to impede virus infectivity in the absence of complement. Antibodies to sites I (B1 and B3) and IV (B6) slowed the rate at which viruses penetrated cell surfaces, supporting the conclusion that antibody binding to gB can inhibit penetration by a virus. The data suggest that MAbs can interfere with penetration by a virus by binding to a domain within gB which is involved in this process. In another assay of virus infection, MAb B6 significantly reduced plaque development, indicating that antibody binding to gB expressed on infected-cell surfaces can also interfere with the ability of a virus to spread from cell to cell. In contrast to these results, antibodies to site II (B2 and B5) had no effect on virus infectivity; this suggests that they recognized structures which do not play a direct role in the infectious process. To localize regions of gB involved in these phenomena, antibody-binding sites were operationally mapped by radioimmunoprecipitation of a panel of truncated gB molecules produced in transient-expression assays. Residues critical to recognition by antibodies which affect penetration by a virus (sites I, III, and IV) mapped to a region of the molecule (amino acid residues 241 to 441) which is centrally located within the external domain. Antibodies which had no effect on penetration (site II) recognized sequences distal to this region (residues 596 to 737) near the transmembrane domain. The data suggest that these gB-specific MAbs recognize two major antigenic sites which reside in physically distinct components of the external domain of gB.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased adherence of human granulocytes to herpes simplex virus type 1 infected endothelial cells

We studied the interaction of human polymorphonuclear leukocytes (PMNs) with umbilical vein endothelial cells infected with herpes simplex virus (HSV) type 1. PMNs labeled with 51Cr were added to endothelial monolayers at varying times after infection and their adherence assessed 1 h later. Granulocyte adherence (GA) to uninfected cells averaged 26.5 +/- 1.9%. Increased adherence began 6 h postinfection and rose to a maximum at 20 to 24 h. HSV-1 glycoproteins seemed to mediate the increase in GA: tunicamycin treatment of infected monolayers for 18 h abolished the increased GA as did incubation of infected cells with F(ab')2 fragments prepared from human antiserum containing HSV-1 antibody.

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.

Epstein-Barr virus glycoprotein homologous to herpes simplex virus gB

The Epstein-Barr virus DNA open reading frame BALF4 (R. Baer, A.T. Bankier, M.D. Biggin, P.L. Deininger, P.J. Farrell, T.J. Gibson, G. Hatfull, G.S. Hudson, S.C. Stachwell, C. Sequin, P.S. Tuffnell, and B.G. Barrell, Nature [London] 310:207-211, 1984), which by nucleotide sequence comparison could encode a protein similar to herpes simplex virus gB (P.E. Pellett, M.D. Biggin, B. Barrell, and B. Roizman, J. Virol. 56:807-813, 1985), has now been shown to encode a 110-kilodalton glycoprotein. Late infectious cycle RNAs of 3.0 and 1.8 kilobases are transcribed from BALF4. Translation of these RNAs in vitro, transcription and translation of BALF4 in vitro, or metabolic labeling of cells in the presence of tunicamycin and immunoprecipitation with BALF4-specific sera results in identification of a 93-kilodalton precursor to gp110. Since N-glycosidase F only reduces the size of gp110 to 105 kilodaltons, gp110 probably has both N- and O-linked glycosylation, gp110 is an abundant glycoprotein in Epstein-Barr virus-infected cells. In infected lymphocytes and in 3T3 cells, in which the gene is expressed from a recombinant expression vector, most of the protein is cytoplasmic and perinuclear. In contrast to gB, gp110 was not detected in the infected-cell plasma membrane. In cells replicating Epstein-Barr virus, gp110 localized to the inner and outer nuclear membrane lamellae and to endoplasmic reticulum structures which sometimes contained enveloped virus. gp110 may play an important role in modifying infected intracellular membranes.

Binding of complement component C3b to glycoprotein gC of herpes simplex virus type 1: mapping of gC-binding sites and demonstration of conserved C3b binding in low-passage clinical isolates

The sites on glycoprotein gC of herpes simplex virus type 1 (HSV-1) which bind complement component C3b were evaluated by using anti-gC monoclonal antibodies and mutants which have alterations at defined regions of the glycoprotein. Monoclonal antibodies were incubated with HSV-1-infected cells in a competitive assay to block C3b binding. Each of 12 different monoclonals, which recognize the four major antigenic sites of gC, completely inhibited C3b binding. With this approach, no one antigenic group on gC could be assigned as the C3b-binding region. Next, 21 gC mutants were evaluated for C3b binding, including 1 which failed to synthesize gC, 4 which synthesized truncated forms of the glycoprotein such that gC did not insert into the cell's membrane, and 16 which expressed gC on the cell's surface but which had mutations in various antigenic groups. Eleven strains did not bind C3b. This included the 1 strain which did not synthesize gC, the 4 strains which secreted gC without inserting the glycoprotein into the cell membrane, and 6 of 16 strains which expressed gC on the cell surface. In these six strains, the mutations were at three different antigenic sites. One hypothesis to explain these findings is that C3b binding is modified by changes in the conformation of gC which develop either after antibodies bind to gC or as a result of mutations in the gC gene. Attachment of C3b to gC was also evaluated in 31 low-passage clinical isolates of HSV-1. Binding was detected with each HSV-1 isolate, but not with nine HSV-2 isolates. Therefore, although mutants that lack C3b binding are readily selected in vitro, the C3b-binding function of gC is maintained in vivo. These results indicate that the sites on gC that bind C3b are different from those that bind monoclonal antibodies, that antibodies directed against all sites on gC block C3b binding, and that C3b binding is a conserved function of gC in vivo.