Host-Cell Lysosomal Response to Two Strains of Herpes Simplex Virus

A correlation has been made between the host lysosomal responses to and release of infectious virus from HEp-2 cells infected with two strains of herpes simplex virus (HSV). Supravital staining with acridine orange was used for morphological studies of macroplaque and microplaque HSV-infected cells. With the progression of infection, cells infected with either microplaque HSV or macroplaque HSV were observed to undergo different lysosomal and cytopathic changes, which could be correlated with increased accumulation of acid phosphatase and infectious virus in the extracellular fluid.     

Herpes simplex virus-specific CD8+ T cells can clear established lytic infections from skin and nerves and can partially limit the early spread of virus after cutaneous inoculation

HSV infects skin or mucosal epithelium as well as entering the sensory nerves and ganglia. We have used TCR-transgenic T cells specific for the immunodominant class I-restricted determinant from HSV glycoprotein B (gB) combined with a flank zosteriform model of infection to examine the ability of CD8+ T cells to deal with infection. During the course of zosteriform disease, virus rapidly spreads from the primary inoculation site in the skin to sensory dorsal root ganglia and subsequently reappears in the distal flank. Virus begins to be cleared from all sites about 5 days after infection when gB-specific CD8+ T cells first appear within infected tissues. Although activated gB-specific effectors can partially limit virus egress from the skin, they do so only at the earliest times after infection and are ineffective at halting the progression of zosteriform disease once virus has left the inoculation site. In contrast, these same T cells can completely clear ongoing lytic replication if transferred into infected immunocompromised RAG-1-/- mice. Therefore, we propose that the role of CD8+ T cells during the normal course of disease is to clear replicating virus after infection is well established rather than limit the initial spread of HSV from the primary site of inoculation.     

Cell-to-cell transmission of HSV1 in human keratinocytes in the absence of the major entry receptor,nectin1

Herpes simplex virus 1 (HSV1) infects the stratified epithelia of the epidermis, oral or genital mucosa, where the main cell type is the keratinocyte. Here we have used nTERT human keratinocytes to generate a CRISPR-Cas9 knockout (KO) of the primary candidate HSV1 receptor, nectin1, resulting in a cell line that is refractory to HSV1 entry. Nonetheless, a small population of KO cells was able to support infection which was not blocked by a nectin1 antibody and hence was not a consequence of residual nectin1 expression. Strikingly at later times, the population of cells originally resistant to HSV1 infection had also become infected. Appearance of this later population was blocked by inhibition of virus genome replication, or infection with a ΔUL34 virus defective in capsid export to the cytoplasm. Moreover, newly formed GFP-tagged capsids were detected in cells surrounding the initial infected cell, suggesting that virus was spreading following replication in the original susceptible cells. Additional siRNA depletion of the second major HSV1 receptor HVEM, or PTP1B, a cellular factor shown elsewhere to be involved in cell-to-cell transmission, had no effect on virus spread in the absence of nectin1. Neutralizing human serum also failed to block virus transmission in nectin1 KO cells, which was dependent on the receptor binding protein glycoprotein D and the cell-to-cell spread glycoproteins gI and gE, indicating that virus was spreading by direct cell-to-cell transmission. In line with these results, both HSV1 and HSV2 formed plaques on nectin1 KO cells, albeit at a reduced titre, confirming that once the original cell population was infected, the virus could spread into all other cells in the monolayer. We conclude that although nectin1 is required for extracellular entry in to the majority of human keratinocytes, it is dispensable for direct cell-to-cell transmission.     

Polarized Cell Migration during Cell-to-Cell Transmission of Herpes Simplex Virus in Human Skin Keratinocytes

In addition to transmission involving extracellular free particles, a generally accepted model of virus propagation is one wherein virus replicates in one cell, producing infectious particles that transmit to the next cell via cell junctions or induced polarized contacts. This mechanism of spread is especially important in the presence of neutralizing antibody, and the concept underpins analysis of virus spread, plaque size, viral and host functions, and general mechanisms of virus propagation. Here, we demonstrate a novel process involved in cell-to-cell transmission of herpes simplex virus (HSV) in human skin cells that has not previously been appreciated. Using time-lapse microscopy of fluorescent viruses, we show that HSV infection induces the polarized migration of skin cells into the site of infection. In the presence of neutralizing antibody, uninfected skin cells migrate to the initial site of infection and spread over infected cells to become infected in a spatially confined cluster containing hundreds of cells. The cells in this cluster do not undergo cytocidal cell lysis but harbor abundant enveloped particles within cells and cell-free virus within interstitial regions below the cluster surface. Cells at the base and outside the cluster were generally negative for virus immediate-early expression. We further show, using spatially separated monolayer assays, that at least one component of this induced migration is the paracrine stimulation of a cytotactic response from infected cells to uninfected cells. The existence of this process changes our concept of virus transmission and the potential functions, virus, and host factors involved.     

Trigeminal ganglion infection by thymidine kinase-negative mutants of herpes simplex virus after in vivo complementation.

Infection of trigeminal ganglion by herpes simplex virus (HSV) thymidine kinase-negative (TK-) mutants was investigated in mixed infection studies in mice. Mice were corneally inoculated with TK- HSV alone or with mixtures of TK- HSV-TK+ HSV. When inoculated alone, an arabinosylthymine-selected HSV type 1 TK- mutant and a HSV type 2 TK- deletion mutant infected mouse ocular tissues but rarely infected ganglion tissues. However, both TK- mutants readily infected ganglion tissues when they were inoculated in mixtures with TK+ HSV. By means of mixed infection studies, it was demonstrated that TK- HSV could readily establish acute and latent ganglion infections. It was thought that the frequent infection of trigeminal ganglion tissue by both TK- mutants after mixed TK(-)-TK+ HSV infection was the result of in vivo complementation. After mixed TK(-)-TK+ HSV infection and subsequent cultivation of ganglion explants in arabinosylthymine, results supported the conclusion that when TK- was present in ganglia it was in the same neurons that contained TK+ HSV.     

Herpesvirus-lymphoid cell interactions: comparative studies on the biology of herpes simplex virus-induced Fc receptors in B, T, and "null" lymphoid cell lines

We have investigated the induction of Fc receptor (FcR) in different types of lymphoid cell lines (LCL) infected with herpes simplex virus (HSV). Subpopulations of certain of these LCL normally express FcR unrelated to herpetic infection. Differentiation of virus-induced FcR from that related to normal cell function was therefore possible. FcR detection was carried out by means of a rosette assay using ox erythrocytes coated with 7S immunoglobulin G (EA rosettes). Both HSV types 1 and 2 were found to induce FcR in B, T, and “null” (i.e., non-B, non-T) type LCL; however, in all the LCL tested, this HSV-induced FcR expression appeared to be more restricted in the responding T LCL than in responding B and null type LCL. In addition, kinetic experiments revealed that the time course of HSV-induced FcR expression differed among these LCL types tested. Interestingly, a number of LCL were resistant to HSV infection or restricted HSV gene expression, including expression of the viral products responsible for FcR induction. In all the responding HSV-infected LCL, induction of FcR always paralleled the expression of HSV antigens. Synthesis of HSV-induced FcR was shown to be inhibited by phosphonoacetic acid, an inhibitor of herpesvirus DNA polymerase activity, whereas FcR of non-HSV origin was found to be resistant to inhibitor. This would infer that HSV codes for an FcR which can be differentiated from that of cellular origin by using phosphonoacetic acid. Therefore, two different mechanisms of FcR synthesis may be suggested, one virus mediated and the second probably under cellular control. In addition, the data obtained using Epstein-Barr virus producer as well as isogeneic monoclonal cell lines, with and without the Epstein-Barr virus genome, indicated that the resident Epstein-Barr virus genome in the target cell did not have a detectable effect in the induction of FcR by HSV.     

Different forms of membrane-associated herpes simplex virus glycoproteins induce functionally distinct subsets of herpes simplex virus-specific suppressor T cells.

Previous studies have shown that two types of virus-specific suppressor T cells (Ts) are induced in mice made tolerant with herpes simplex virus (HSV)-infected spleen cells (SC). One type of Ts blocks the afferent phase of the delayed hypersensitivity response to HSV (Ts-aff), and the other blocks the efferent or effector phase (Ts-eff). In this report we show that the induction requirements for these suppressor populations differ. Injection of SC infected for 6 h with HSV at a multiplicity of infection of 5 or less or treated with heat-inactivated virus induced only Ts-aff. Similar results were seen with SC incubated for 90 min in virus-free preparations containing only viral proteins. In contrast, the Ts-eff population was induced only by SC treated for 6 h with infectious HSV at a multiplicity of infection of 10. Collectively, these data indicate that Ts-aff are induced by adsorbed HSV antigens on SC, whereas Ts-eff are induced by nascent HSV antigens expressed on infected SC. In addition to their induction requirements, the two types of regulatory cells differ in their expression of effector function. Ts-eff but not Ts-aff require a cyclophosphamide-sensitive target cell in the immune recipient for suppressor function. The possible identity of this target cell and the significance of the different induction requirements between the two types of Ts are discussed.     

Deoxyribonucleic Acid Synthesis in Synchronized Mammalian KB Cells Infected with Herpes Simplex Virus

We examined the patterns of host cell and virus deoxyribonucleic acid (DNA) synthesis in synchronized cultures of KB cells infected at different stages of the cell cycle with herpes simplex virus (HSV). We found that the initiation of HSV DNA synthesis, we well as the production of new infectious virus, is independent of the S, G1, and G2 phases of the mitotic cycle of the host cell. This is in contrast to data previously found with equine abortion virus. Because HSV replicates independently of the cell cycle, we were able to establish conditions that would permit the study of rates of HSV DNA synthesized in logarithmically growing cells in the virtual absence of cellular DNA synthesis. This eliminates the need for separation of viral and cellular DNA by isopycnic centrifugation in CsCl. We found that HSV DNA synthesis was initiated between 2 to 3 hr after infection. The rate of DNA synthesis increased rapidly, reaching a maximum 4 hr after infection, and decreased to 50% of maximum by 8 hr. Evidence is also presented which suggests that HSV infection can inhibit both the ongoing synthesis of host DNA as well as the initiation of the S phase.     

Induction of uracil-DNA glycosylase and dUTP nucleotidohydrolase activity in herpes simplex virus-infected human cells

HeLa BU cells infected with either the type 1 or the type 2 forms of herpes simplex virus show an increase in the activities of uracil-DNA glycosylase and dUTP nucleotidohydrolase. Under optimal conditions, uracil-DNA glycosylase activity increases approximately 40-fold in HSV type 2-infected cells. In herpes simplex virus (HSV) type 1-infected cells, uracil-DNA glycosylase activity increases only 6-fold. At a KCl concentration of 100 mM, uracil-DNA glycosylase derived from HSV type 2-infected cells is activated 2-fold, while the glycosylase extracted from mock infected HeLa BU cells is inhibited almost 90% at 100 mM KCl. dUTP nucleotidohydrolase activity increases 4-fold and 3-fold, respectively, in HSV type 1- and HSV type 2-infected HeLa BU cells. Nondenaturing polyacrylamide gel electrophoresis of extracts derived from the type 1- and type 2-infected cells indicates distinct electrophoretic mobilities from the host cell enzyme. dUTP nucleotidohydrolase RF values for the mock infected cells, HSV type 1, and HSV type 2 are 0.5, 0.25, and 0.33, respectively. Serum from rabbits immunized against cells infected with herpes simplex virus type 1 or type 2 specifically neutralizes the dUTPase and uracil-DNA glycosylase activities extracted from herpes simplex virus-infected cells. This serum does not neutralize dUTPase or uracil-DNA glycosylase activity derived from mock infected cells.     

Proteomic analysis of cells in the early stages of herpes simplex virus type‐1 infection reveals widespread changes in the host cell proteome

During infection by herpes simplex virus type‐1 (HSV‐1) the host cell undergoes widespread changes in gene expression and morphology in response to viral replication and release. However, relatively little is known about the specific proteome changes that occur during the early stages of HSV‐1 replication prior to the global damaging effects of virion maturation and egress. To investigate pathways that may be activated or utilised during the early stages of HSV‐1 replication, 2‐DE and LC‐MS/MS were used to identify cellular proteome changes at 6 h post infection. Comparative analysis of multiple gels representing whole cell extracts from mock‐ and HSV‐1‐infected HEp‐2 cells revealed a total of 103 protein spot changes. Of these, 63 were up‐regulated and 40 down‐regulated in response to infection. Changes in selected candidate proteins were verified by Western blot analysis and their respective cellular localisations analysed by confocal microscopy. We have identified differential regulation and modification of proteins with key roles in diverse cellular pathways, including DNA replication, chromatin remodelling, mRNA stability and the ER stress response. This work represents the first global comparative analysis of HSV‐1 infected cells and provides an important insight into host cell proteome changes during the early stages of HSV‐1 infection.     

The spread of herpes simplex virus type 1 from trigeminal neurons to the murine cornea: an immunoelectron microscopy study

An animal model has been developed to clarify the mechanism for spread of herpes simplex virus (HSV) from neuron to epithelial cells in herpetic epithelial keratitis. HSV was introduced into the murine trigeminal ganglion via stereotaxic guided injection. After 2 to 5 days, the animals were euthanized. Ganglia and corneas were prepared for light and electron microscopic immunocytochemistry with antisera to HSV. At 2 days, labeled axons were identified in the stromal layer. At 3 days, we could detect immunoreactive profiles of trigeminal ganglion cell axons that contained many vesicular structures. By 3 and 4 days, the infection had spread to all layers of epithelium, and the center of a region of infected epithelium appeared thinned. At 5 day, fewer basal cells appeared infected, although infection persisted in superficial cells where it had expanded laterally. Mature HSV was found in the extracellular space surrounding wing and squamous cells. Viral antigen was expressed in small pits along the apical surfaces of wing and squamous cells but not at the basal surface of these cells or on basal cells. This polarized expression of viral antigen resulted in the spread of HSV to superficial cells and limited lateral spread to neighboring basal cells. The pathogenesis of HSV infection in these mice may serve as a model of the human recurrent epithelial disease in the progression of focal sites of infection and transfer from basal to superficial cells.     

In vitro establishment of lytic and nonproductive infection by herpes simplex virus type 1 in three-dimensional keratinocyte culture.

The F strain of herpes simplex virus type 1 (HSV-1) was tested for its ability to produce lytic or nonproductive infection in squamous epithelial cells cultured in a three-dimensional organotypic tissue culture. For the tissue culture, we used HaCat cells (immortalized skin keratinocytes) and normal fibroblasts derived from the skin. The cultures were infected with HSV-1 (5 PFU) either when the epithelial cells had grown as a monolayer with a confluence of 80% on the collagen fibroblast gel or 30 min after lifting of the epithelial cells into the air-liquid interface. The cultures were collected 1 week after inoculation. Typical cytopathic effects of HSV infection (ballooning and reticular degeneration with multinucleate giant cells) were seen only in those cultures in which the epithelial cells were infected before lifting. The presence of HSV was confirmed by DNA and RNA in situ hybridization and PCR. No morphological changes were found in cultures infected after lifting into the air-liquid interface. No infectious virus was recovered either from cells or culture supernatant. However, these cultures were positive for HSV DNA on PCR and showed expression of the LAT gene by in situ hybridization and Northern blot (RNA) hybridization. The present results indicate that both nonproductive and lytic HSV infection can be produced in vitro and the outcome of the infection depends on the time of viral inoculation in relation to epithelial maturation.     

Virus Type-Specific Thymidine Kinase in Cells Biochemically Transformed by Herpes Simplex Virus Types 1 and 2

Transformation of mouse cells (Ltk(-)) and human cells (HeLa Bu) from a thymidine kinase (TK)-minus to a TK(+) phenotype (herpes simplex virus [HSV]-transformed cells) has been induced by infection with ultraviolet-irradiated HSV type 2 (HSV-2), as well as by HSV type 1 (HSV-1). Medium containing methotrexate, thymidine, adenine, guanosine, and glycine was used to select for cells able to utilize exogenous thymidine. We have determined the kinetics of thermal inactivation of TK from cells lytically infected with HSV-1 or HSV-2 and from HSV-1- and HSV-2-transformed cells. Three hours of incubation at 41 C produces a 20-fold decrease in the TK activity of cell extracts from HSV-2-transformed cells and Ltk(-) cells lytically infected with HSV-2. The same conditions produce only a twofold decrease in the TK activities from HSV-1-transformed cells and cells lytically infected with HSV-1. This finding supports the hypothesis that an HSV structural gene coding for TK has been incorporated in the HSV-transformed cells.     

Quantitative polymerase chain reaction analysis of herpes simplex virus DNA in ganglia of mice infected with replication-incompetent mutants.

To study the roles of viral genes in the establishment and maintenance of herpes simplex virus (HSV) latency, we have developed a polymerase chain reaction assay that is both quantitative and sensitive. Using this assay, we analyzed the levels of viral DNA in trigeminal ganglia of mice inoculated corneally with HSV mutants that are defective for virus replication at one or more sites in mice and for reactivation upon ganglionic explant. Ganglia from mice infected with thymidine kinase-negative mutants, which replicate at the site of inoculation and establish latency but do not replicate acutely in ganglia or reactivate upon explant, contained a range of levels of HSV DNA that overlapped with the range found in ganglia latently infected with wild-type virus. On average, these mutant-infected ganglia contained one copy of HSV DNA per 100 cell equivalents (ca. 10(4) molecules), which was 50-fold less than the average for wild-type virus. Ganglia from mice infected with a ribonucleotide reductase deletion mutant, which is defective for acute replication and reactivation upon ganglionic explant, also contained on average one copy of HSV DNA per 100 cell equivalents. We also detected substantial numbers of HSV DNA molecules (up to ca. 10(3] in ganglia of mice infected with an ICP4 deletion mutant and other replication-negative mutants that are severely impaired for viral DNA replication and gene expression. These results raise the possibility that such mutants can establish latency, which could have important implications for mechanisms of latency and for vaccine and antiviral drug development.     

Herpes Simplex Virus type 1 infects Langerhans cells and the novel epidermal dendritic cell,Epi-cDC2s,via different entry pathways

Skin mononuclear phagocytes (MNPs) provide the first interactions of invading viruses with the immune system. In addition to Langerhans cells (LCs), we recently described a second epidermal MNP population, Epi-cDC2s, in human anogenital epidermis that is closely related to dermal conventional dendritic cells type 2 (cDC2) and can be preferentially infected by HIV. Here we show that in epidermal explants topically infected with herpes simplex virus (HSV-1), both LCs and Epi-cDC2s interact with HSV-1 particles and infected keratinocytes. Isolated Epi-cDC2s support higher levels of infection than LCs in vitro, inhibited by acyclovir, but both MNP subtypes express similar levels of the HSV entry receptors nectin-1 and HVEM, and show similar levels of initial uptake. Using inhibitors of endosomal acidification, actin and cholesterol, we found that HSV-1 utilises different entry pathways in each cell type. HSV-1 predominantly infects LCs, and monocyte-derived MNPs, via a pH-dependent pathway. In contrast, Epi-cDC2s are mainly infected via a pH-independent pathway which may contribute to the enhanced infection of Epi-cDC2s. Both cells underwent apoptosis suggesting that Epi-cDC2s may follow the same dermal migration and uptake by dermal MNPs that we have previously shown for LCs. Thus, we hypothesize that the uptake of HSV and infection of Epi-cDC2s will stimulate immune responses via a different pathway to LCs, which in future may help guide HSV vaccine development and adjuvant targeting.     

HSV hepatitis in the mouse: a light and electron microscopic study with immunohistology and in situ hybridization

In order to characterize better the morphology and immune response in acute necrotizing HSV infection, murine HSV hepatitis was examined. BALB/c mice were inoculated intraperitoneally with 10(6) plaque-forming units (PFU) of HSV-1 (Lenette) and HSV-2 (D316). In both groups half the animals were pretreated with silica particles to block macrophage function. Up to 6 days after infection four mice from each group were sacrificed at daily intervals and the livers were examined by light and electron microscopy, immunohistology, in situ hybridization, combined immunohistology/in situ hybridization and titration of viral PFU. HSV-2 infected mice developed severe necrotizing hepatitis with persistence of HSV in the liver tissue until the end of the study. HSV-1 infected mice rapidly eliminated the virus and revealed only small necrotic foci. Early phase alterations and necrotic phase lesions were distinguished and characterized and morphologic evidence of a direct cytopathic effect of HSV was detected. A specific immune reaction in late stages appeared to be mediated by T4-positive T-lymphocytes. In situ hybridization and immunohistochemistry showed a close correlation with virus titration and were valuable in characterizing early phases and in the assessment of prognosis and differential diagnosis.