Direct and sensitive detection of a human virus by rupture event scanning

We have developed a sensitive, economical method that directly detects viruses by making use of the interaction between type 1 herpes simplex virus (HSV1) and specific antibodies covalently attached to the oscillating surface of a quartz crystal microbalance (QCM). The virions were detached from the surface by monotonously increasing the amplitude of oscillation of the QCM, while using the QCM to sensitively detect the acoustic noise produced when the interactions were broken. We term this process rupture event scanning (REVS). The method is quantitative over at least six orders of magnitude, and its sensitivity approaches detection of a single virus particle.

Assembly and organization of glycoproteins B, C, D, and H in herpes simplex virus type 1 particles lacking individual glycoproteins: No evidence for the formation of a complex of these molecules

Glycoprotein B (gB), gC, gD, and gH:L of herpes simplex virus type 1 (HSV-1) are implicated in virus adsorption and penetration. gB, gD, and gH:L are essential for these processes, and their expression is necessary and sufficient to induce cell fusion. The current view is that these molecules act in concert as a functional complex, and cross-linking studies support this view (C. G. Handler, R. J. Eisenberg, and G. H. Cohen, J. Virol. 70:6067-6075, 1996). We examined the glycoprotein composition, with respect to gB, gC, gD, and gH, of mutant virions lacking individual glycoproteins and the sedimentation characteristics of glycoproteins extracted from these virions. The amounts of gB, gC, gD, or gH detected in virions did not alter when any one of these molecules was absent, and it therefore appears that they are incorporated into the virion independently of each other. The sedimentation characteristics of gB and gD from mutant virions were not different from those of wild-type virions. We confirmed that gB, gC, and gD could be cross-linked to each other on the virion surface but found that the absence of one glycoprotein did not alter the outcome of cross-linking reactions between the remaining molecules. The incorporation and arrangement of these glycoproteins in the virion envelope therefore appear to be independent of the individual molecular species. This is difficult to reconcile with the concept that gB, gC, gD, and gH:L are incorporated as a functional complex into the virion envelope.

Effects of targeting herpes simplex virus type 1 gD to the endoplasmic reticulum and trans-Golgi network

Glycoprotein D (gD) of herpes simplex virus type 1 (HSV-1) was modified to encode targeting signals known to localize proteins to either the endoplasmic reticulum (ER) or the trans-Golgi network. These motifs conferred the predicted targeting properties on gD in transfected cells as judged by immunofluorescence staining, and the exclusion of targeted gD from the cell surface was confirmed by the fact that these molecules exhibited substantially reduced activity in cell-cell fusion assays. Recombinant viruses expressing Golgi-targeted forms of gD grew to wild-type levels in noncomplementing cells, exhibited unaltered particle/infectivity ratios, and were found to contain wild-type levels of gD, whereas a recombinant expressing ER-retained gD was helper cell dependent and, when grown on noncomplementing cells, produced virions of low specific infectivity with greatly reduced levels of gD. These data imply that HSV-1 acquires its final membrane from a post-ER compartment and lend support to the view that the virus undergoes de-envelopment and reenvelopment steps during virus egress.

Glycoprotein C-deficient mutants of two strains of herpes simplex virus type 1 exhibit unaltered adsorption characteristics on polarized or non-polarized cells

Mutants of herpes simplex virus type 1 (HSV-1) strain SC16, lacking each of the dispensable glycoproteins C, G, E, I or J, were examined for their ability to infect the apical or basolateral surfaces of polarized human epithelial cells. None of the mutants was significantly different from the wild-type parent when assayed on either surface. Since a previous report had demonstrated that glycoprotein C (gC) was necessary for the infection of apical surfaces of polarized epithelium, a second gC-negative mutant was constructed on a background of HSV-1 strain HFEM. This mutant displayed no phenotype when assayed on the apical surface. Furthermore, neither gC-negative mutant differed from its wild-type parent in its adsorption kinetics or specific infectivity on non-polarized Vero cells, a result which is inconsistent with the view that interactions between gC and cell surface proteoglycans constitute the initial adsorption process. Our findings thus conflict with previous reports and suggest that proposed functions of HSV-1 gC in the infection of polarized and non-polarized cells may be strain-dependent.

Glycoproteins gB, gD, and gHgL of herpes simplex virus type 1 are necessary and sufficient to mediate membrane fusion in a Cos cell transfection system

Herpes simplex virus type 1 glycoproteins gB, gD, and gHgL were expressed by transient transfection of Cos cells. Polykaryocyte formation above the background level seen in untransfected controls was observed only if all three components were expressed. Thus, gB, gD, and gHgL are necessary and sufficient to induce membrane fusion.

Site-directed and linker insertion mutagenesis of herpes simplex virus type 1 glycoprotein H

The gH-gL complex of herpes simplex virus type 1 (HSV-1) is essential for virion infectivity and virus-induced cell fusion, but functional domains of the gH molecule remain to be defined. We have addressed this question by mutagenesis. A set of linker insertion mutants in HSV-1 gH was generated and tested in transient assays for their ability to complement a gH-negative virus. Insertions at three sites in the C-terminal third of the external domain affected the ability of gH to function in cell-cell fusion and virus entry, while insertions at six sites in the N-terminal half of the external domain induced conformational changes in gH such that it was not recognized by monoclonal antibody LP11, although expression at the cell surface was unchanged. A recombinant virus in which a potential integrin-binding motif, RGD, in gH was changed to the triplet RGE entered cells as efficiently as the wild type, indicating that HSV-1 entry is not mediated by means of the gH-RGD motif binding to cell surface integrins. Furthermore, mutagenesis of the glycosylation site which is positionally conserved in all herpesvirus gH sequences in close proximity to the transmembrane domain generated a recombinant virus that grew in vitro with wild-type single-step kinetics.

An endoplasmic reticulum-retained herpes simplex virus glycoprotein H is absent from secreted virions: evidence for reenvelopment during egress

Although it is generally accepted that one of the first steps of herpesvirus egress is the acquisition of an envelope by nucleocapsids budding into the inner nuclear membrane, later events in the pathway are not well understood. We tested the hypothesis that the virus then undergoes de-envelopment, followed by reenvelopment at membranes outside the endoplasmic reticulum (ER), by constructing a recombinant virus in which the expression of an essential glycoprotein, gH, is restricted to the inner nuclear membrane-ER by means of the ER retention motif, KKXX. This targeting signal conferred the predicted ER localization properties on gH in recombinant virus-infected cells, and gH and gL polypeptides failed to become processed to their mature forms. Cells infected with the recombinant virus released particles with 100-fold less infectivity than those released by cells infected with the wild-type parent virus, yet the number of enveloped virus particles released into the medium was unaltered. These particles contained normal amounts of gD and VP16 but did not contain detectable amounts of gH, and these data are consistent with a model of virus exit whereby naked nucleocapsids in the cytoplasm acquire their final envelope from a subcellular compartment other than the ER-inner nuclear membrane.

Analysis of the contributions of herpes simplex virus type 1 membrane proteins to the induction of cell-cell fusion

The contributions of a set of herpes simplex virus type 1 membrane proteins towards the process of cell-cell fusion were examined with a series of deletion mutants into which a syncytial mutation had been introduced at codon 855 of the glycoprotein B (gB) gene. Analysis of the fusion phenotypes of these recombinant viruses in Vero cells revealed that while gC, gG, US5, and UL43 are dispensable for syncytium formation at both high and low multiplicities of infection, gD, gHgL, gE, gI, and gM were all required for the fusion of cellular membranes. These data confirm that the requirements for virion entry and cell-cell fusion are not identical. gD and gHgL, like gB, are essential for both processes. gG, gI, and gM, on the other hand, are dispensable for virus penetration, yet play a role in cell-to-cell spread by the direct contact route, at least on an SC16 gBANG background.

An analysis of the in vitro and in vivo phenotypes of mutants of herpes simplex virus type 1 lacking glycoproteins gG, gE, gI or the putative gJ

Mutants of herpes simplex virus type 1 (HSV-1) lacking glycoproteins gG, gE, gI or the putative gJ were constructed by inserting a lacZ expression cassette within the US4, US8, US7 and US5 genes respectively. Revertant viruses were then constructed by rescue with a wild-type DNA fragment. Each of these mutant viruses, by comparison with the parental virus HSV-1 SC16, exhibited normal particle to infectivity ratios, and had no discernible phenotypic abnormalities in baby hamster kidney-21 cells following high or low multiplicity infections. Infection of mice by scarification of the ear with these mutant viruses showed the following. (i) Interruption of the US5 (gJ) gene has no effect on the ability of HSV-1 to multiply at the inoculation site or its ability to enter or multiply in the peripheral or central nervous system (CNS). This shows that the US5 gene provides a convenient site for the insertion of foreign genes for both in vitro and in vivo studies. (ii) Disruption of the US4 (gG) gene results in marginal attenuation in the mouse ear model. (iii) Disruption of the US7 (gI) or US8 (gE) genes results in pronounced attenuation; virus was rapidly cleared from the inoculation site and was barely detectable in sensory ganglia or in the CNS. The failure of gI-negative or gE-negative viruses to replicate efficiently at the inoculation site in vivo led to the investigation of virus behaviour in epithelial cells in vitro. Viruses lacking gE or gI adsorbed to and entered these cells at normal rates compared with the parental virus, but formed minute plaques. This is consistent with a failure of cell-to-cell spread by the cell contact route. This was confirmed by measurement of the rate of increase in infectious centre numbers following low multiplicity infections. The view that gE and gI influence interactions between cells at the plasma membrane was reinforced by showing that the introduction of disrupted gE or gI genes into a syncytial, but otherwise syngeneic, background resulted in a non-syncytial phenotype. We conclude that the gE-gI complex plays a part, at least in some cell types, in the interactions at the cell surface that allow transmission of the virus from infected to uninfected cells by cell contact. In syncytial strains this leads to uncontrolled membrane fusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of protective immune responses to the glycoprotein H-glycoprotein L complex of herpes simplex virus type 1

A recombinant vaccinia virus expressing both glycoprotein H (gH) and glycoprotein L (gL) of herpes simplex virus type 1 (HSV-1) was used to examine the protective response to gH-gL in immunized mice and to compare these responses with those induced by the highly protective immunogen, glycoprotein D (gD). Weak levels of HSV-1-specific neutralizing antibody were obtained in response to the gH-gL complex, virus clearance from the site of challenge was marginally enhanced compared to that observed following immunization with gH alone, and gH-gL was found to protect mice against acute infection in the ganglia, although not as efficiently as gD.

Construction and characterization of a human cytomegalovirus mutant with the UL18 (class I homolog) gene deleted

The UL18 open reading frame of human cytomegalovirus (HCMV) (which encodes a product homologous to major histocompatibility complex class I heavy chains) has been disrupted by insertion of the beta-galactosidase gene under control of the major HCMV early promoter. The recombinant virus delta UL18 showed no phenotypic differences from wild-type HCMV in terms of single-step growth curves or particle/infectivity ratios, indicating that the UL18 gene product is dispensable for the growth of HCMV in human fibroblasts in vitro. The synthesis of the mature cellular class I heterodimer is shut down in cells infected at a high multiplicity with wild-type HCMV, and a similar effect was seen in delta UL18-infected fibroblasts, suggesting that although the UL18 gene product can associate with beta 2 microglobulin, it is not directly involved in the disruption of class I assembly.

The UL16 gene of human cytomegalovirus encodes a glycoprotein that is dispensable for growth in vitro

The UL16 gene of human cytomegalovirus (HCMV) encodes a predicted translation product with features characteristic of glycoproteins (signal and anchor sequences and eight potential N-linked glycosylation sites). Antisera were raised against the UL16 gene product expressed in Escherichia coli as a beta-galactosidase fusion protein. The antisera detected a 50-kDa glycoprotein in HCMV-infected cells that was absent from purified virions. The UL16 glycoprotein was synthesized at early times after infection and accumulated to the highest levels at late times after infection. A recombinant HCMV in which UL16 coding sequences were interrupted by a lacZ expression cassette was constructed by insertional mutagenesis. Analysis of the phenotype of the recombinant virus indicated that the UL16 gene product is nonessential for virus infectivity and growth in tissue culture.

Construction and properties of a mutant of herpes simplex virus type 1 with glycoprotein H coding sequences deleted

A mutant of herpes simplex virus type 1 (HSV-1) in which glycoprotein H (gH) coding sequences were deleted and replaced by the Escherichia coli lacZ gene under the control of the human cytomegalovirus IE-1 gene promoter was constructed. The mutant was propagated in Vero cells which contained multiple copies of the HSV-1 gH gene under the control of the HSV-1 gD promoter and which therefore provide gH in trans following HSV-1 infection. Phenotypically gH-negative virions were obtained by a single growth cycle in Vero cells. These virions were noninfectious, as judged by plaque assay and by expression of beta-galactosidase following high-multiplicity infection, but partial recovery of infectivity was achieved by using the fusogenic agent polyethylene glycol. Adsorption of gH-negative virions to cells blocked the adsorption of superinfecting wild-type virus, a result in contrast to that obtained with gD-negative virions (D. C. Johnson and M. W. Ligas, J. Virol. 62:4605-4612, 1988). The simplest conclusion is that gH is required for membrane fusion but not for receptor binding, a conclusion consistent with the conservation of gH in all herpesviruses.

Production of human papillomavirus type 16 virions in a keratinocyte cell line

Human papillomavirus type 16 (HPV-16) is strongly associated with carcinoma of the cervix, but the complete life cycle of the virus cannot be studied because no experimental system is available in which HPV-16 progeny are produced, and there is currently no source of HPV-16 virus particles. Most cell lines that harbor HPV-16 DNA contain the viral genome as integrated or concatenated DNA in which open reading frames are disrupted or deleted, but a human cervical keratinocyte cell line has been described which maintains HPV-16 DNA in monomeric episomal form (M.A. Stanley, H.M. Brown, M.W. Appleby, and A.C. Minson, Int. J. Cancer 43:672-676, 1989). This cell line was induced to form a stratified differentiating epithelium by grafting onto nude mice. Long-term grafts displayed the histological features of a low-grade cervical dysplasia, and terminally differentiated cells contained amplified levels of HPV-16 DNA, virus capsid antigen, and virus particles. This experimental system appears to permit the completion of the HPV-16 life cycle in virus-containing keratinocytes.

A complex between the MHC class I homologue encoded by human cytomegalovirus and beta 2 microglobulin

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that persists in the host and can cause severe disease in the immunocompromised individual or in the fetus. Analysis of the nucleotide sequence of the virus genome has revealed the presence of an open reading frame whose predicted translation product has homology with the heavy chain of the major histocompatibility complex (MHC) class I molecule of higher eukaryotes, and the observed sequence homology was given additional significance by the independent observation that HCMV virions can bind beta 2 microglobulin (beta 2m), the light chain of the MHC class I molecule. We expressed both the HCMV class I homologue and the human beta 2m gene in recombinant vaccinia viruses. We show that the coexpressed gene products associate, that the transport of beta 2m to the cell surface is dependent on coexpression of the class I homologue and that the viral gene product is therefore functionally related to its cellular counterpart. We observe also that, in HCMV-infected cells, no synthesis of mature cellular class I molecules occurs, while messenger RNA levels remain unaltered, and we speculate that one function of the viral homologue may be to sequester beta 2m, thus preventing the maturation of cellular class I molecules and rendering the infected cell unrecognizable by cytotoxic T cells.

Induction of immunoglobulin G Fc receptors by recombinant vaccinia viruses expressing glycoproteins E and I of herpes simplex virus type 1

Glycoprotein E (gE) of herpes simplex virus type 1 (HSV-1) will bind immunoglobulin G (IgG) (Fc) affinity columns (R. B. Bauke and P. G. Spear, J. Virol. 32:779-789, 1979), but recent evidence suggests that the HSV-1 Fc receptor is composed of a complex of gE and glycoprotein I (gI) and that both gI and gE are required for Fc receptor activity (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987; D. C. Johnson, M. C. Frame, M. W. Ligas, A. M. Cross, and N. D. Stow, J. Virol. 62:1347-1354, 1988). We have expressed gE and gI, either alone or in combination, on the surface of HeLa cells by using recombinant vaccinia viruses and have measured Fc receptor activity by Fc-rosetting or IgG-binding assays. Expression of gE alone resulted in the induction of Fc receptor activity, while expression of gI alone gave no detectable Fc binding. Coexpression of gE and gI resulted in higher levels of IgG binding than did expression of gE alone, despite the fact that under conditions of coexpression, the levels of surface gE were reduced. We propose that gE and gI together form a receptor of higher affinity than gE alone and that HSV-1 therefore has the potential to induce two Fc receptors of different affinities.