Interactions between herpes simplex virus and murine bone marrow macrophages

Signal transducer and activator of transcription 3 (Stat3) regulates host defense and protects mice against herpes simplex virus-1 (HSV-1) infection

Signal transducer and activator of transcription 3 (STAT3) mediates cellular responses to multiple cytokines, governs gene expression, and regulates the development and activation of immune cells. STAT3 also modulates reactivation of latent herpes simplex virus-1 (HSV-1) in ganglia. However, it is unclear how STAT3 regulates the innate immune response during the early phase of HSV-1 lytic infection. Many cell types critical for the innate immunity are derived from the myeloid lineage. Therefore, in this study, we used myeloid-specific Stat3 knockout mice to investigate the role of STAT3 in the innate immune response against HSV-1. Our results demonstrate that Stat3 knockout bone marrow-derived macrophages (BMMs) expressed decreased levels of interferon-α (IFN-α) and interferon-stimulated genes (ISGs) upon HSV-1 infection. In vivo, knockout mice were more susceptible to HSV-1, as marked by higher viral loads and more significant weight loss. Splenic expression of IFN-α and ISGs was reduced in the absence of STAT3, indicating that STAT3 is required for optimal type I interferon response to HSV-1. Expression of TNF-α and IL-12, cytokines that have been shown to limit HSV-1 replication and pathogenesis, was also significantly lower in knockout mice. Interestingly, Stat3 knockout mice failed to expand the CD8⁺ conventional DC (cDC) population upon HSV-1 infection, and this was accompanied by impaired NK and CD8 T cell activation. Collectively, our data demonstrate that myeloid-specific Stat3 deletion causes defects in multiple aspects of the immune system and that STAT3 has a protective role at the early stage of systemic HSV-1 infection.

[18F]FHPG positron emission tomography for detection of herpes simplex virus (HSV) in experimental HSV encephalitis

Herpes simplex virus type 1 (HSV-1) is one of the most common causes of sporadic encephalitis. The initial clinical course of HSV encephalitis (HSE) is highly variable, and the infection may be rapidly fatal. For effective treatment with antiviral medication, an early diagnosis of HSE is crucial. Subtle brain infections with HSV may be causally related to neuropsychiatric disorders such as Alzheimer's dementia. We investigated the feasibility of a noninvasive positron emission tomography (PET) imaging technique using [(18)F]FHPG as a tracer for the detection of HSE. For this purpose, rats received HSV-1 (infected group) or phosphate-buffered saline (control group) by intranasal application, and dynamic PET scans were acquired. In addition, the distribution of tracer accumulation in specific brain areas was studied with phosphor storage imaging. The PET images revealed that the overall brain uptake of [(18)F]FHPG was significantly higher for the infected group than for control animals. Phosphor storage images showed an enhanced accumulation of [(18)F]FHPG in regions known to be affected after intranasal infection with HSV. High-performance liquid chromatography metabolite analysis showed phosphorylated metabolites of [(18)F]FHPG in infected brains, proving that the increased [(18)F]FHPG uptake in infected brains was due to HSV thymidine kinase-mediated trapping. Freeze lesion experiments showed that damage to the blood-brain barrier could in principle induce elevated [(18)F]FHPG uptake, but this nonspecific tracer uptake could easily be discriminated from HSE-derived uptake by differences in the tracer kinetics. Our results show that [(18)F]FHPG PET is a promising tool for the detection of HSV encephalitis.

Application of a systemic herpes simplex virus type 1 infection in the rat as a tool for sunscreen photoimmunoprotection studies

The application of a novel model for sunscreen photoimmunoprotection studies was assessed using a systemic infection of rats with herpes simplex virus type 1 (HSV-1). Rats were irradiated daily with 1 minimal erythemal/oedematous dose of UVB for 7 consecutive days on their shaved backs with or without application of a broad-spectrum sunscreen (containing TiO2) with a sun protection factor of 10. Subsequently, rats were infected intranasally with HSV. UV exposure prior to HSV infection induced increased severity and incidence of clinical signs of disease, suppression of cellular immune responses as assessed by delayed type hypersensitivity and increased viral load in the brain. The sunscreen provided protection against all these UV-induced effects. We conclude that this novel model is a promising way of testing the immunoprotective qualities of sunscreens, based on the response to a common infectious agent of human subjects.

Effects of UV irradiation on skin and nonskin-associated herpes simplex virus infections in rats

Herpes simplex virus (HSV) normally causes vescular lesions on mucocutaneous surfaces but can also cause encephalitis. The virus can reactivate from the latent state in neurons to form recrudescent lesions. One common stimulus for reactivation is exposure to sunlight. In the present study, the effects of irradiating rats with suberythemal ultraviolet (UV) before or after infecting them epidermally with HSV was investigated. Preexposure to UV impaired HSV-specific cellular immune responses, as indicated by delayed type hypersensitivity (DTH) and in vitro lymphoproliferation assays. However, the number and severity of the skin lesions were not altered. In contrast, exposure after infection did not affect cellular immunity but resulted in a large increase in the severity and number of lesions. In a second series of experiments, the effects of preirradiating with UV on HSV infection was examined using a route of inoculation which was not skin-associated, namely intranasal, allowing direct non-invasive access to the nervous system. It was found that suppressed DTH resulted, together with an increase in the incidence and severity of neurological symptoms and an increased viral load in the brain. Therefore, unlike the situation in the skin, irradiation of rats before intranasal inoculation led to a suppressed immune response to HSV which correlated with increased viral load and symptoms. These results indicate that the effects of UV may be dependent on whether the animal is exposed before or after the infection, and whether the infection is skin-associated or systemic.

Antigen presentation in patients with recrudescent orofacial herpes simplex virus infections

Recovery from epidermal herpes simplex virus (HSV) infection depends primarily on development of an effective cell-mediated immune response, possibly generated following antigen (Ag) presentation by epidermal cells (EC). The ability of EC to present HSV Ag was investigated in 12 subjects with occasional recrudescent facial HSV infections. All had circulating HSV specific antibodies and cell-mediated immunity to the virus. Peripheral blood mononuclear cell suspensions, depleted of antigen presenting cells (APC) by glass adherence and then enriched for T cells by adsorption on nylon wool columns, did not proliferate in response to HSV Ag. Both EC suspensions, prepared from suction blister roofs, and glass-adherent peripheral blood mononuclear cells (AC) preincubated with ultraviolet-inactivated HSV, reconstituted the T-cell proliferative response to HSV. EC were more efficient than AC at presenting HSV Ag to T cells. Depletion of CD1+ cells from EC suspensions by cell sorting reduced their ability to present HSV Ag and augmentation of CD1+ cell numbers supplemented it. Preincubation of EC or AC with monoclonal antibodies to major histocompatibility complex class II antigens DP, DQ or DR, blocked the lymphoproliferative response to HSV Ag. Evidence was obtained that cells co-ordinately expressing products of the DP, DQ and DR loci are involved in presentation of HSV Ag by both EC and AC.

Persistent infection with herpes simplex virus type 1 in an Ia antigen-positive murine macrophage cell line

The interaction of herpes simplex virus type 1 (HSV-1) with murine macrophage cell lines was examined. The cell lines appeared to be moderately permissive for HSV-1 replication, though the yield of the virus was limited compared with that in Vero cells. Furthermore, the murine macrophage cell line SL-1, bearing Ia antigen, was persistently infected with HSV-1 for over one year, and was designated SL-1/KOS. Persistent infection could not be established in an Ia antigen-negative macrophage cell line, SL-4. In the SL-1/KOS culture, there was a small number of infected cells as revealed by infectious center assay. Treatment with monoclonal antibody against HSV-1 cured the persistent infection. Therefore maintenance of the persistent infection is considered to be due to a carrier culture consisting of a minority of infected cells and a majority of uninfected cells. In the SL-1/KOS cultures a low level of interferon (IFN) was found. When a large amount of exogenous recombinant murine IFN-beta (10(5)-10(6) international units/ml) was added to the culture, virus production diminished to undetectable levels. These results suggest that IFN plays an important role in the maintenance of persistent infection. In long-term persistently infected cultures, syncytium formation appeared and the virus from such cultures had a different DNA structure from that of the virus originally used for infection as revealed by restriction endonuclease analysis.

Two phenotypically distinct T cells are involved in ultraviolet-irradiated urocanic acid-induced suppression of the efferent delayed-type hypersensitivity response to herpes simplex virus, type 1 in vivo

When UVB-irradiated urocanic acid, the putative photoreceptor/mediator for UVB suppression, is administered to mice it induces a dose-dependent suppression of the delayed-type hypersensitivity response to herpes simplex virus, type 1 (HSV-1), of similar magnitude to that induced by UV irradiation of mice. In this study, the efferent suppression of delayed-type hypersensitivity by UV-irradiated urocanic acid is demonstrated to be due to 2 phenotypically distinct T cells, (Thy1+, L3T4-, Ly2+) and (Thy1+, L3T4+, Ly2-). The suppression is specific for HSV-1. This situation parallels the generation of 2 distinct T-suppressor cells for HSV-1 by UV irradiation of mice and provides further evidence for the involvement of urocanic acid in the generation of UVB suppression.