Cellular neuroimmunologic responses to ocular herpes simplex virus infection

Repeated social stress enhances the innate immune response to a primary HSV-1 infection in the cornea and trigeminal ganglia of Balb/c mice

Three to 5 days after a primary HSV-1 infection, macrophages infiltrate into the trigeminal ganglia (TG) and produce anti-viral cytokines to reduce viral replication. Previous research demonstrated that social disruption stress (SDR) enhances the trafficking of monocytes/macrophages from the bone marrow to the spleen and increases pro-inflammatory cytokine production in vitro and in vivo. The impact of SDR on the trafficking of these cells to loci of herpes simplex virus type 1 (HSV-1) infection and subsequent function has not been examined. The following studies were designed to determine whether SDR would enhance the innate immune response during a primary HSV-1 infection by increasing the number of macrophages in the cornea and TG, thus increasing anti-viral cytokine production and reducing viral replication. BALB/c mice were exposed to six cycles of SDR prior to ocular infection with HSV-1 McKrae virus. Flow cytometric analysis of cells from the TG revealed an increase in the percentage of CD11b+ macrophages in SDR mice compared to controls. Immune cell infiltration into the cornea, however, could not be determined due to low cell numbers. Although gene expression of IFN-beta was decreased, SDR increased gene expression of IFN-alpha, and TNF-alpha, in the cornea and TG. Examination of viral proteins showed decreased expression of infected cell protein 0 (ICP0), glycoprotein B (gB), glycoprotein H (gH) and latency-associated transcript (LAT) in the TG, however, expression of ICP0 and gB were elevated in the cornea of SDR mice. These results indicate that the innate immune response to HSV-1 was altered and enhanced by the experience of repeated social defeat.

Why do we lack an effective vaccine against herpes simplex virus infections?

This review discusses the possible causes for the lack of an effective antiherpes vaccine. Future prospects of vaccines based on the current knowledge of immune responses to herpes viruses are discussed. It is argued that vaccines capable of expanding CD8 T-cell memory responses should be the focus of future anti-herpes simplex virus research.

Macrophage Control of Herpes Simplex Virus Type 1 Replication in the Peripheral Nervous System

After corneal infection, herpes simplex virus type 1 (HSV-1) invades sensory neurons with cell bodies in the trigeminal ganglion (TG), replicates briefly, and then establishes a latent infection in these neurons. HSV-1 replication in the TG can be detected as early as 2 days after corneal infection, reaches peak titers by 3–5 days after infection, and is undetectable by 7–10 days. During the period of HSV-1 replication, macrophages and γδ TCR+ T lymphocytes infiltrate the TG, and TNF-α, IFN-γ, the inducible nitric oxide synthase (iNOS) enzyme, and IL-12 are expressed. TNF-α, IFN-γ, and the iNOS product nitric oxide (NO) all inhibit HSV-1 replication in vitro. Macrophage and γδ TCR+ T cell depletion studies demonstrated that macrophages are the main source of TNF-α and iNOS, whereas γδ TCR+ T cells produce IFN-γ. Macrophage depletion, aminoguanidine inhibition of iNOS, and neutralization of TNF-α or IFN-γ all individually and synergistically increased HSV-1 titers in the TG after HSV-1 corneal infection. Moreover, individually depleting macrophages or neutralizing TNF-α or IFN-γ markedly reduced the accumulation of both macrophages and γδ TCR+ T cells in the TG. Our findings establish that after primary HSV-1 infection, the bulk of virus replication in the sensory ganglia is controlled by macrophages and γδ TCR+ T lymphocytes through their production of antiviral molecules TNF-α, NO, and IFN-γ. Our findings also strongly suggest that cross-regulation between these two cell types is necessary for their accumulation and function in the infected TG.

Toxicity studies in thymidine kinase-deficient herpes simplex virus therapy for malignant astrocytoma

Previous studies have shown that genetically engineered thymidine kinase (tk)-defective herpes simplex virus type 1 (HSV-1) can effectively and selectively destroy gliomas in animal models. The consequences of viral infection and tumor regression must be characterized before this therapy can be applied in human trials. To study the potential for long-term toxicity, immunocompetent rats harboring 9L gliosarcomas were injected intratumorally with a tk-defective HSV-1, KOS-SB, at titers that previously have been demonstrated to cause tumor regression. In animals surviving 3 months or longer following viral treatment, there was no evidence of persistent infection or inflammation in peritumoral brain tissue or in remote systemic organs studied with routine histological and immunocytochemical analyses. Polymerase chain reaction using primers specific for HSV-1 detected HSV-1 DNA in peritumoral tissue only in animals sacrificed within 3 months of viral injection. There was no evidence of HSV-1 DNA in systemic tissues at any time after treatment. We conclude that stereotactic intratumoral injection of tk-deficient HSV can be attempted for the treatment of brain tumors without risk of systemic infection or significant toxicity to normal brain or remote proliferating tissues.

Gamma interferon expression during acute and latent nervous system infection by herpes simplex virus type 1

This study was initiated to evaluate a role for gamma interferon (IFN-gamma) in herpes simplex virus type 1 (HSV-1) infection. At the acute stage of infection in mice, HSV-1 replication in trigeminal ganglia and brain stem tissue was modestly but consistently enhanced in mice from which IFN-gamma was by ablated monoclonal antibody treatment and in mice genetically lacking the IFN-gamma receptor (Rgko mice). As determined by reverse transcriptase PCR, IFN-gamma and tumor necrosis factor alpha transcripts were present in trigeminal ganglia during both acute and latent HSV-1 infection. CD4+ and CD8+ T cells were detected initially in trigeminal ganglia at day 5 after HSV-1 inoculation, and these cells persisted for 6 months into latency. The T cells were focused around morphologically normal neurons that showed no signs of active infection, but many of which expressed HSV-1 latency-associated transcripts. Secreted IFN-gamma was present up to 6 months into latency in areas of the T-cell infiltration. By 9 months into latency, both the T-cell infiltrate and IFN-gamma expression had cleared, although there remained a slight increase in macrophage levels in trigeminal ganglia. In HSV-1-infected brain stem tissue, T cells and IFN-gamma expression were present at 1 month but were gone by 6 months after infection. Our hypothesis is that the persistence of T cells and the sustained IFN-gamma expression occur in response to an HSV-1 antigen(s) in the nervous system. This hypothesis is consistent with a new model of HSV-1 latency which suggests that limited HSV-1 antigen expression occurs during latency (M. Kosz-Vnenchak, J. Jacobson, D.M. Coen, and D.M. Knipe, J. Virol. 67:5383-5393, 1993). We speculate that prolonged secretion of IFN-gamma during latency may modulate a reactivated HSV-1 infection.

Drug-induced taste and smell disorders. Incidence, mechanisms and management related primarily to treatment of sensory receptor dysfunction

Drugs in every major pharmacological category can impair both taste and smell function and do so more commonly than presently appreciated. Impairment usually affects sensory function at a molecular level, causing 2 major behavioural changes--loss of acuity (i.e. hypogeusia and hyposmia) and/or distortion of function (i.e. dysgeusia and dysosmia). These changes can impair appetite, food intake, cause significant lifestyle changes and may require discontinuation of drug administration. Loss of acuity occurs primarily by drug inactivation of receptor function through inhibition of tastant/odorant receptor: (i) binding; (ii) Gs protein function; (iii) inositol trisphosphate function; (iv) channel (Ca++,Na++) activity; (v) other receptor inhibiting effects; or (vi) some combination of these effects. Distortions occur primarily by a drug inducing abnormal persistence of receptor activity (i.e. normal receptor inactivation does not occur) or through failure to activate: (i) various receptor kinases; (ii) Gi protein function; (iii) cytochrome P450 enzymes; or other effects which usually (iv) turn off receptor function; (v) inactivate tastant/odorant receptor binding; or (vi) some combination of these effects. Termination of drug therapy is commonly associated with termination of taste/smell dysfunction, but occasionally effects persist and require specific therapy to alleviate symptoms. Treatment primarily requires restoration of normal sensory receptor growth, development and/or function. Treatment which restores sensory acuity requires correction of steps initiating receptor and other pathology and includes zinc, theophylline, magnesium and fluoride. Treatment which inhibits sensory distortions requires reactivation of biochemical inhibition at the receptor or inactivation of inappropriate stimulus receptor binding and/or correction of other steps initiating pathology including dopaminergic antagonists, gamma-aminobutyric acid (GABA)-ergic agonists, calcium channel blockers and some orally active local anaesthetic, antiarrhythmic drugs.

A platelet-activating factor antagonist reduces corneal allograft inflammation and neovascularization

We assessed the role of platelet-activating factor (PAF) in corneal allograft rejection and evaluated the effects of a PAF antagonist on corneal inflammation, cellular infiltration, vascularization, and edema. Rabbits with vascularized corneas served as recipients of allogeneic cornea grafts. Rabbits with normal corneas underwent autografts as controls. All of the allografts developed the progression of signs characteristic of rejection. Nevertheless, treatment with the PAF antagonist BN52021 significantly inhibited corneal allograft vascularization for up to 10 days after transplantation and reduced the number of eosinophils in the allografts at 28 days after transplantation. In contrast, saline-treated allografts exhibited florid vascularization and intense inflammatory infiltrates. Control autografts survived without developing significant inflammation or vascularization. The retardation of allograft eosinophilia and graft vascularization by the PAF antagonist was most likely the result of suppression of PAF-mediated reactions in the cornea. These results indicate that PAF may play a role in corneal inflammation and vascularization after corneal transplantation, and that PAF antagonists may be clinically useful in delaying some of the pathophysiologic consequences of corneal graft rejection.

Herpes simplex virus type-2 infection by a footpad route results in neuronal death in mouse spinal ganglia

We have examined the effects of herpes simplex virus type 2 (HSV-2) infection on neuron numbers in mouse dorsal root ganglia (DRG) following unilateral hind footpad inoculation. One month following HSV-2 strain MS inoculation, tissue sections of decalcified spine containing the paired 4th and 5th lumbar DRGs were stained with cresyl violet. Neuronal numbers, somal areas and ganglion volumes were determined for ganglia ipsilateral and contralateral to both HSV-2 and medium inoculations. One month following HSV-2 infection, 47-88% of neurons disappeared in the ipsilateral ganglia. The somal areas of the remaining neurons in these ganglia fell within the range of the uninfected population. Ganglionic shrinkage did not occur as a result of HSV-2 infection; neurons were replaced by large numbers of inflammatory cells. Neuron numbers in the contralateral control ganglia of the HSV-2 inoculated mice appeared slightly decreased. Mice inoculated with medium contained similar numbers of neurons in ipsilateral and contralateral ganglia. These results show that, in addition to other previously described host alterations, infection with HSV-2 strain MS results in neuronal death in the affected host ganglia. This is the first in vivo quantitative documentation of neuronal death induced by herpes simplex virus infection.