In-vivo modulation of macrophage functions by herpes simplex virus type 2 in resistant and sensitive inbred mouse strains

HSV-2 vaccine: current state and insights into development of a vaccine that targets genital mucosal protection

HSV-2 is one of the most prevalent sexually transmitted infections that result in significant morbidity and financial burden on health systems around the world. Recurrent and asymptomatic re-activation accompanied by viral shedding is common among sero-positive individuals, leading to relatively high efficiency of transmission. Prophylactic HSV-2 vaccines are the best and cheapest option to address the problems associated with HSV-2 infections globally. However, despite persistent efforts, the search for an efficacious vaccine for HSV-2 remains elusive. In this review, the current state of HSV-2 vaccines and the outcome of past human trials are examined. Furthermore, we discuss the evidence and strategies from experimental mouse models that have been successful in inducing protective immunity in the genital tract against HSV-2, following immunization. Future vaccination strategies that focus on induction of robust mucosal immunity in the genital tract may hold the key for a successful vaccine against HSV-2.

Of mice and not humans: how reliable are animal models for evaluation of herpes CD8(+)-T cell-epitopes-based immunotherapeutic vaccine candidates?

Herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2)-specific CD8(+) T cells that reside in sensory ganglia, appear to control recurrent herpetic disease by aborting or reducing spontaneous and sporadic reactivations of latent virus. A reliable animal model is the ultimate key factor to test the efficacy of therapeutic vaccines that boost the level and the quality of sensory ganglia-resident CD8(+) T cells against spontaneous herpes reactivation from sensory neurons, yet its relevance has been often overlooked. Herpes vaccinologists are hesitant about using mouse as a model in pre-clinical development of therapeutic vaccines because they do not adequately mimic spontaneous viral shedding or recurrent symptomatic diseases, as occurs in human. Alternatives to mouse models are rabbits and guinea pigs in which reactivation arise spontaneously with clinical herpetic features relevant to human disease. However, while rabbits and guinea pigs develop spontaneous HSV reactivation and recurrent ocular and genital disease none of them can mount CD8(+) T cell responses specific to Human Leukocyte Antigen- (HLA-)restricted epitopes. In this review, we discuss the advantages and limitations of these animal models and describe a novel "humanized" HLA transgenic rabbit, which shows spontaneous HSV-1 reactivation, recurrent ocular disease and mounts CD8(+) T cell responses to HLA-restricted epitopes. Adequate investments are needed to develop reliable preclinical animal models, such as HLA class I and class II double transgenic rabbits and guinea pigs to balance the ethical and financial concerns associated with the rising number of unsuccessful clinical trials for therapeutic vaccine formulations tested in unreliable mouse models.

Exacerbation of autoantibody-mediated hemolytic anemia by viral infection

Strong enhancement of the pathogenicity of an antierythrocyte monoclonal antibody was observed after infection of mice with lactate dehydrogenase-elevating virus. While injection of the antierythrocyte antibody alone induced only moderate anemia, concomitant infection with this virus, which is harmless in most normal mice, led to a dramatic drop in the hematocrit and to death of infected animals. In vitro and in vivo analyses showed a dramatic increase in the ability of macrophages from infected mice to phagocytose antibody-coated erythrocytes. These results indicate that viruses can trigger the onset of autoimmune disease by enhancing the pathogenicity of autoantibodies. They may explain how unrelated viruses could be implicated in the etiology of autoantibody-mediated autoimmune diseases.

Spread of herpes simplex virus type 1 in the central nervous system during experimentally reactivated encephalitis

Because many of the features of reactivated herpes simplex virus type 1 (HSV-1) central nervous systems (CNS) infections in vivo are incompletely understood, we used an animal model to study the development of the morphological, ultrastructural, radiological and immunological changes which occurred during acute and experimentally reactivated diseases. Rabbits were intranasally inoculated with HSV-1, and their latent trigeminal ganglionic and CNS infections were reactivated by intravenous injection of cyclophosphamide and dexamethasone. Technetium brain scans were performed to localize areas of blood-brain barrier breakdown, and cerebrospinal fluid (CSF) was analysed for IgG content by radial immunodiffusion assays. Nervous system tissues were studied by in situ hybridization and by immunofluorescent, light and electron microscopic techniques. Diffuse uptake of technetium was observed as HSV-1 spread transsynaptically into the brain during the acute phase of infection, and viral antigens and nucleic acids were detected in both the CNS olfactory and trigeminal systems. During latency, viral RNA was detected in the nuclei of neurons within the CNS olfactory cerebral and entorhinal cortices, indicating that HSV-1 became latent within the same CNS structures that were involved during the acute phase of infection. Following drug-induced reactivation, the brain scans revealed a more focal breakdown of the blood-brain barrier, and both neurons and neuronal processes in the entorhinal and olfactory cortices contained viral nucleic acids which correlated with the ultrastructural presence of HSV-1 virions. During the reactivated phase of infection a marked increase in the CSF IgG index occurred without an increase in the CSF: serum albumen ratio indicating a prompt intrathecal response in infected rabbits as compared to controls. To some extent, the CSF IgG index reflected the degree of histopathological damage.

In vitro comparison between four variants of Aujeszky's disease virus

Four Aujeszky's disease (pseudorabies) virus variants were characterized in vitro by investigation of their resistance to heat at 48 degrees C, sensitivity to trypsin and ability to replicate in pig alveolar macrophages, two of these variants (Ls-1 and Ls-2) were cloned previously from a single isolate of virus and showed differing pathogenicity for pigs; the virulent Stanley strain; and the non-virulent NIA-4 strain were included for comparison. Heat treatment produced slight decreases in infectivity but no significant differences were observed in the rates of inactivation. Both Ls-1 and Ls-2 were significantly more sensitive to trypsin treatment than the other two. The comparison of progeny virus titres after replication in alveolar macrophages allowed further differentiation among variants. Ls-1 and Ls-2 had similar titres in cultures infected with high virus input but in cultures infected with low virus input (0.1 TCID50/cell) Ls-1 produced higher titre. The difference in titres at 48 h post-infection was statistically significant (P less than 0.05). The cytopathogenicity for macrophages of the strains was correlated with their virulence for pigs, Stanley strain being the most cytopathogenic and NIA-4 the least.

Herpes simplex virus, type 1 invasion of the rabbit and mouse nervous systems revealed by in situ hybridization

Using a 3H-labelled virion DNA probe applied to tissue sections, we have previously identified the precise microscopic anatomical location of herpes simplex virus (HSV) during the acute and latent stages of infection of the mouse trigeminal ganglia and central nervous system (CNS). In the present investigation, we compared the mouse and the rabbit with respect to their ability to support acute and latent infections of trigeminal ganglionic and central nervous system neurons. We found that HSV-1, strain F, produced acute and latent infection of trigeminal ganglion cells in both mice and rabbits; however, lower levels of HSV-1 RNA were expressed in rabbit neurons as compared to mouse neurons, and many fewer neurons of the rabbit supported an acute infection than in the mouse. Studies of the trigeminal system within the CNS revealed that HSV-1 established latency more readily in the mouse than in the rabbit. The histopathology observed in acutely infected rabbit brain was less intense and less widespread than in mouse brain.

Replication of HSV-1 in murine peritoneal macrophages: comparison of various virus strains with different properties

The in vitro replication of eleven different strains of herpes simplex virus type 1 was studied in resident or thioglycollate-stimulated mouse macrophages. The strains of herpes simplex virus differed in the type of cytopathic effect, induction capacity for herpes simplex virus coded thymidine kinase and pathogenicity in the mouse. Herpes simplex virus replicated better in thioglycollate-stimulated macrophages than in resident macrophages. In vitro ageing of macrophages increased their replicative potency. Herpes simplex virus replicated better in macrophages from homozygous bg/bg C57/BL6J mice than in macrophages from their heterozygous littermates. Separation of macrophages on discontinuous Percoll-gradients revealed 4 fractions with identical potency for replication. The ability of herpesvirus to replicate in macrophages varied from strain to strain of virus i.e. Wal greater than Len, clone 4 of Len, greater than L3-2s, JES, Ang-, Ang + path, clone 2 of Len and greater than MDK clones. The ability to cause cytopathology also varied. Only strains Ang- and Ang + path showed limited or late cytopathology in macrophages. The cell-fusing property of herpes simplex virus appeared to be more closely correlated with lower replication rates than production cell rounding. Thymidine kinase- viruses replicated less well than thymidine kinase+ or thymidine kinase(+) strains. Strains of herpes simplex virus with high or low pathogenicity for mice replicated in macrophages to the same degree. The phagocytic activity of macrophages for IgM-coated sheep red blood cells was inhibited earlier by strains of herpes simplex virus of type 2 than by strains of herpes simplex virus of type 1.

Experimental infection of inbred mice with herpes simplex virus. VI. Effect of interferon on in vitro virus replication in macrophages

Peritoneal exudate cells (PEC) of DBA/2 mice, after 7 days of in vitro preculture and consisting of virtually 100 per cent macrophages, were able to support the replication of Herpes Simplex Virus type 1 strain WAL (HSV). Using a standard medium based on Dulbecco's Modified Eagle Medium (D-MEM), no virus replication was observed in freshly isolated PEC. However a medium based on RPMI 1640 consistently yielded higher virus titres in precultured PEC than the D-MEM medium, and also allowed virus replication in freshly isolated PEC. Macrophages derived from the spleens or the bone marrow, and precultured in the same way as PEC represented a highly pure population and were permissive for infection with HSV. Titres of about 10(6) PFU HSV were observed in PEC 48 hours after infection with 10(3) or 10(6) PFU. However, whereas a complete destruction of the cell monolayer was observed 24 hours after infection with 10(6) PFU, complete cytopathogenicity in PEC infected with 10(3) PFU required at least twice this time. In the latter situation, plaque formation was observed 24 hours after infection. PEC of different strains of mice were compared. Of these, PEC of all mice that are susceptible to HSV infection in vivo replicated HSV to the same degree as PEC of DBA/2 mice, whereas PEC of resistant C57BL/6 and C3H/HeJ mice produced 1000 fold lower titres of viral progeny. Whereas the number of infectious centres were equal in PEC of DBA/2 and C57BL/6 mice, the plaques observed after infection of confluent PEC with a low MOI were considerable smaller in cells from C57BL/6 mice. Furthermore, significantly higher titres of interferon were measured in the supernatants of HSV-infected C57BL/6 macrophages than in those of DBA/2 macrophages, and the former were made fully susceptible by the in vitro addition of an anti-interferon serum.

Experimental infection of inbred mice with herpes simplex virus. IV. Comparison of interferon production and natural killer cell activity in susceptible and resistant adult mice

Inbred mouse strains differ in susceptibility to infection with herpes simplex virus type 1 or type 2 (HSV-1, HSV-2). In this study interferon production was tested in the peritoneal exudate of mice after intraperitoneal (i.p.) injection of HSV-1 or HSV-2. In HSV-resistant mice (C57 BL/6, C3 H/HeJ) high titers of interferon were already present 2 to 4 hours after injection. In comparison, less resistant mice (DBA/2, AKR) lacked this early response. There was no correlation between interferon titers and resistance at post-infection times later than twelve hours. At twelve hours, however, high titers of HSV were detected in the peritoneum of DBA/2 mice and significantly lower titers in C57 BL/6 mice. In a comparative analysis of eight different inbred mouse strains, again early (2 to 4 hours) interferon production was correlated to resistance. In assays of HSV-stimulated early (24 hours) NK cell responses not only the good interferon producer strains but also one of the less resistant low interferon producers (BALB/c) showed significant cytotoxic activities. Conversely, SJL mice that are very low in HSV-induced NK cell activity are resistant and show high early interferon responses at the local site.

Effects of genetic resistance against Herpes simplex virus in vaginally infected mice

In order to take the conditions of natural Herpes simplex virus (HSV) infection into consideration, the genetic resistance of C57-Bl mice, which was established by intraperitoneal HSV-1 infection [Lopez, 1975], was investigated in vaginally infected mice. The course of infection in the mucous membranes did not differ in sensitive (NMRI) and resistant (C57-Bl) mice: both number of takes and virus elimination from the vagina were equal, and no difference in viral titer produced in the vagina was detected. Viral titer in the productively infected lumbosacral ganglia, however, was less in the resistant mice. An experiment with foot-pad-infected mice confirmed that the number of productively infected ganglia was reduced in resistant mice, and contralateral ganglia were infected only in the sensitive mouse strain. In spite of this, the number of latently infected animals did not vary significantly in the mouse strains. Higher activity of defense mechanisms in resistant mice, apparently localized in the ganglia, resulted in reduced lethality. As to the mechanisms of the resistance, neither antibody nor interferon response were enhanced in C57-Bl mice, but resistance was abolished by depletion of several cellular functions, i.e., lymphocytes by cyclophosphamide or X-rays, macrophages by silica or macrophage-antiserum, and M-cells by 89Sr.

Murine cellular cytotoxicity to syngeneic and xenogeneic herpes simplex virus-infected cells

Cellular cytotoxicity of C57BL/6 adult mice peritoneal cells to xenogeneic (Chang liver) and syngeneic (BL/6-WT3) herpes simplex virus (HSV)-infected cells was analyzed in a 6-h 51Cr release assay. There was no difference in antibody-dependent cellular cytotoxicity to either target. There was no natural killer cytotoxicity to targets with cells from uninfected mice except at very high effector cell ratios. HSV-infected (2 X 10(4) PFU intraperitoneally 1 day previously) mice mediated significantly higher antibody-dependent cellular cytotoxicity and required less antibody (10(-5) versus 10(-2) dilution), fewer cells, and less time to kill than cells from uninfected mice. HSV-infected mice mediated natural killer cytotoxicity but preferentially killed syngeneic HSV-infected cells. Stimulation of cytotoxicity was not virus specific since influenza-infected mice mediated similar levels of cytotoxicity to HSV-infected targets. There was no difference in morphology (95% macrophage) or in the percentage of FcR-positive cells, but infected mice had more peritoneal cells and generated higher levels of superoxide in response to opsonized zymosan or phorbolmyristate acetate. These data demonstrate nonspecific virus-stimulated metabolic and effector cell function which may enhance clearance of virus in an infected host.

Resistance to infections in mice with defects in the activities of mononuclear phagocytes and natural killer cells: effects of immunomodulators in beige mice and 89Sr-treated mice

Beige mice, which are a homolog of the Chediak-Higashi syndrome, and mice treated with 89Sr to destroy the bone marrow provide animal models of defects in mononuclear phagocyte and natural killer cell functions. The innate resistance of these mice to viruses such as herpes simplex and encephalomyocarditis viruses, however, is normal. Moreover, treatment of the mice with immunomodulators such as Propionibacterium acnes (formerly designated Corynebacterium parvum) and pyran produced a significant increase in resistance to encephalomyocarditis virus. The antiviral effect of P. acnes in 89Sr-treated mice was exhibited during marked monocytopenia and without evidence for an inflammatory influx of macrophages into the peritoneal cavity. Treatment with P. acnes was also effective in increasing the resistance of beige mice to infection with Listeria monocytogenes. Thus, immunomodulators can be effective in mice that exhibit impaired macrophage and natural killer cell functions.

Studies on the interrelation of resistance and immunity in a mouse model system of herpes-simplex type 2 infection

Intraperitoneal (i.p.) vaccination of mice with attenuated herpes simplex virus type 2 (HSV 2) induced solid protection to i.p. infection with pathogenic virus within two days. Protection was non-virus-specific until day four after sensitization but increased in specificity thereafter. Normal mice could be protected by adoptively transferred spleen cells, serum, and peritoneal fluid from donors vaccinated seven days before. Virus-specific effector cells induced in the spleen by in vivo i.p. sensitization with either live, pathogenic, or attenuated virus and tested in a cytotoxicity assay were exclusively B lymphocytes. No functional B cells, but natural killer (NK) cells, could be detected in the unseparated peritoneal exudate cell (PEC) population. Ability to generate HSV 2 specific antibody responses did not correlate with natural resistance.

Modulation by cyclosporin A of murine natural resistance against herpes simplex virus infection. I. Interference with the susceptibility to herpes simplex virus infection

Adult BALB/c mice which are medium-high resistant against intraperitoneal (i.p.) infection with herpes simplex virus type 2 (HSV-2) manifested a drastic increase in susceptibility to the virus when treated locally with cyclosporin A (CyA) during infection. Oral application of the drug had no effect on the natural resistance status. Mice appeared normal 2 weeks after CyA treatment with regard to their ability to resist i.p. infections. CyA did not interfere with established specific immune protection nor with the induction in immune responses to HSV-2.

Modulation by cyclosporin A of murine natural resistance against herpes simplex virus infection. II. Influence on the HSV-induced natural killer cell responses, macrophage activities and interferon levels

Cyclosporin A (CyA) interfered locally at the site of injection with several resistance functions which are of potential importance in experimental herpes simplex virus (HSV) infections of mice. HSV-induced stimulation of macrophage phagocytosis was reduced by CyA when the mice were infected 5 days before the assay. The in vitro replication of the virus in macrophages, however, was enhanced. Natural killer (NK) cell response were severely impaired. To some extent this could be attribute to the induction of suppressive macrophages by the drug treatment. Interferon levels induced by HSV were not diminished but rather enhanced in some experiments. Inhibitory effects ceased after termination of CyA treatment and could be prevented by presensitization of the mice with attenuated HSV type 2.