Herpes keratitis.

Herpes simplex virus-1 (HSV-1) infects the majority of the world's population. These infections are often asymptomatic, but ocular HSV-1 infections cause multiple pathologies with perhaps the most destructive being herpes stromal keratitis (HSK). HSK lesions, which are immunoinflammatory in nature, can recur throughout life and often cause progressive corneal scaring resulting in visual impairment. Current treatment involves broad local immunosuppression with topical steroids along with antiviral coverage. Unfortunately, the immunopathologic mechanisms defined in animal models of HSK have not yet translated into improved therapy. Herein, we review the clinical epidemiology and pathology of the disease and summarize the large amount of basic research regarding the immunopathology of HSK. We examine the role of the innate and adaptive immune system in the clearance of virus and the destruction of the normal corneal architecture that is typical of HSK. Our goal is to define current knowledge of the pathogenic mechanisms and recurrent nature of HSK and identify areas that require further study.

Gamma interferon can prevent herpes simplex virus type 1 reactivation from latency in sensory neurons.

We recently demonstrated that CD8(+) T cells could block herpes simplex virus type 1 (HSV-1) reactivation from latency in ex vivo trigeminal ganglion (TG) cultures without destroying the infected neurons. Here we establish that CD8(+) T-cell prevention of HSV-1 reactivation from latency is mediated at least in part by gamma interferon (IFN-gamma). We demonstrate that IFN-gamma was produced in ex vivo cultures of dissociated latently infected TG by CD8(+) T cells that were present in the TG at the time of excision. Depletion of CD8(+) T cells or neutralization of IFN-gamma significantly enhanced the rate of HSV-1 reactivation from latency in TG cultures. When TG cultures were treated with acyclovir for 4 days to insure uniform latency, supplementation with recombinant IFN-gamma blocked HSV-1 reactivation in 80% of cultures when endogenous CD8(+) T cells were present and significantly reduced and delayed HSV-1 reactivation when CD8(+) T cells or CD45(+) cells were depleted from the TG cultures. The effectiveness of recombinant IFN-gamma in blocking HSV-1 reactivation was lost when its addition to TG cultures was delayed by more than 24 h after acyclovir removal. We propose that when the intrinsic ability of neurons to inhibit HSV-1 gene expression is compromised, HSV-specific CD8(+) T cells are rapidly mobilized to produce IFN-gamma and perhaps other antiviral cytokines that block the viral replication cycle and maintain the viral genome in a latent state.

CD8(+) T cells can block herpes simplex virus type 1 (HSV-1) reactivation from latency in sensory neurons.

Recurrent herpes simplex virus type 1 (HSV-1) disease usually results from reactivation of latent virus in sensory neurons and transmission to peripheral sites. Therefore, defining the mechanisms that maintain HSV-1 in a latent state in sensory neurons may provide new approaches to reducing susceptibility to recurrent herpetic disease. After primary HSV-1 corneal infection, CD8(+) T cells infiltrate the trigeminal ganglia (TGs) of mice, and are retained in latently infected ganglia. Here we demonstrate that CD8(+) T cells that are present in the TGs at the time of excision can maintain HSV-1 in a latent state in sensory neurons in ex vivo TG cultures. Latently infected neurons expressed viral genome and some expressed HSV-1 immediate early and early proteins, but did not produce HSV-1 late proteins or infectious virions. Addition of anti-CD8alpha monoclonal antibody 5 d after culture initiation induced HSV-1 reactivation, as demonstrated by production of viral late proteins and infectious virions. Thus, CD8(+) T cells can prevent HSV-1 reactivation without destroying the infected neurons. We propose that when the intrinsic capacity of neurons to inhibit HSV-1 reactivation from latency is compromised, production of HSV-1 immediate early and early proteins might activate CD8(+) T cells aborting virion production.

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 gammadelta TCR+ T lymphocytes infiltrate the TG, and TNF-alpha, IFN-gamma, the inducible nitric oxide synthase (iNOS) enzyme, and IL-12 are expressed. TNF-alpha, IFN-gamma, and the iNOS product nitric oxide (NO) all inhibit HSV-1 replication in vitro. Macrophage and gammadelta TCR+ T cell depletion studies demonstrated that macrophages are the main source of TNF-alpha and iNOS, whereas gammadelta TCR+ T cells produce IFN-gamma. Macrophage depletion, aminoguanidine inhibition of iNOS, and neutralization of TNF-alpha or IFN-gamma all individually and synergistically increased HSV-1 titers in the TG after HSV-1 corneal infection. Moreover, individually depleting macrophages or neutralizing TNF-alpha or IFN-gamma markedly reduced the accumulation of both macrophages and gammadelta 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 gammadelta TCR+ T lymphocytes through their production of antiviral molecules TNF-alpha, NO, and IFN-gamma. Our findings also strongly suggest that cross-regulation between these two cell types is necessary for their accumulation and function in the infected TG.

B7 costimulatory requirements of T cells at an inflammatory site.

The requirement for T cell costimulation at sites of infection and inflammation is unresolved. Herpes stromal keratitis (HSK) is a CD4+ T cell-regulated inflammatory response to herpes simplex virus type 1 infection of the cornea. Our findings suggest that susceptibility to HSK is determined by the microenvironment of the infected cornea. The cornea is normally devoid of Langerhans cells (LC), but these APC are present in the surrounding conjunctiva, and migrate into the cornea following infection. The costimulatory molecule B7-2 was constitutively expressed on LC in conjunctiva, but B7-1 was not detectable until 3 days postinfection. LC were the only cells in the cornea that expressed B7-1 through 7 days postinfection. B7-1 was expressed on some, but not all, migrating LC, suggesting that LC migration and B7-1 expression can be independently regulated. The early LC migration and B7-1 expression was independent of T cells, but T cells were required for the massive accumulation of B7-1+ LC in the cornea at the onset of inflammation. Local inhibition of B7-1 function within the infected cornea prevented HSK. Locally blocking B7-2 function did not reduce HSK incidence, but markedly reduce HSK severity. This is the first direct demonstration that naturally expressed B7 is required within an inflammatory site.

Infected cell protein (ICP)47 enhances herpes simplex virus neurovirulence by blocking the CD8+ T cell response.

The herpes simplex virus (HSV) infected cell protein (ICP)47 blocks CD8+ T cell recognition of infected cells by inhibiting the transporter associated with antigen presentation (TAP). In vivo, HSV-1 replicates in two distinct tissues: in epithelial mucosa or epidermis, where the virus enters sensory neurons; and in the peripheral and central nervous system, where acute and subsequently latent infections occur. Here, we show that an HSV-1 ICP47- mutant is less neurovirulent than wild-type HSV-1 in mice, but replicates normally in epithelial tissues. The reduced neurovirulence of the ICP47- mutant was due to a protective CD8+ T cell response. When compared with wild-type virus, the ICP47- mutant expressed reduced neurovirulence in immunologically normal mice, and T cell-deficient nude mice after reconstitution with CD8+ T cells. However, the ICP47- mutant exhibited normal neurovirulence in mice that were acutely depleted of CD8+ T cells, and in nude mice that were not reconstituted, or were reconstituted with CD4+ T cells. In contrast, CD8+ T cell depletion did not increase the neurovirulence of an unrelated, attenuated HSV-1 glycoprotein (g)E- mutant. ICP47 is the first viral protein shown to influence neurovirulence by inhibiting CD8+ T cell protection.

An immunologist's view of herpes simplex keratitis: Thygeson Lecture 1996, presented at the Ocular Microbiology and Immunology Group meeting, October 26, 1996.

PURPOSE: To review recent progress in understanding the mechanisms of herpes simplex virus 1 (HSV-1)-induced immunopathology in the cornea, as revealed by studies in a mouse model. METHODS: The corneas of A/J mice were infected with 5 x 10(4) plaque-forming units (PFU) of the RE strain of HSV-1, and the development of inflammation was assessed by slitlamp, histologic, or immunohistochemical examination. The immunopathologic mechanisms were then defined by observing the effect of in vivo depletion of corneal Langerhans' cells, or T-lymphocyte subpopulations, or in vivo neutralization of cytokines on adhesion molecule expression or leukocytic infiltration of the infected cornea. RESULTS: After corneal infection, 60-70% of mice develop corneal opacity due to leukocytic infiltration, neovascularization, and edema. Polymorphonuclear neutrophils (PMN) represent 90% of the infiltrating cells, with numerous CD4+, but few CD8+, T cells present. Depleting CD4+ T cells of Langerhans' cells prevents inflammation from developing. Neutralizing interleukin-2 (IL-2) or interferon gamma (IFN-gamma) can prevent inflammation or cause a remission of existing disease. IFN-gamma neutralization causes a rapid block of PMN extravasation from the blood in association with reduced platelet endothelial cell adhesion molecule 1 (PECAM-1) expression on the corneal vascular endothelium. IL-2 neutralization results in decreased IFN-gamma production, reduced chemotaxis, and loss of PMN viability in the infected cornea. CONCLUSION: Herpes stromal keratitis is a CD4+ T cell-dependent inflammatory process in which PMN infiltration and destruction of the cornea are regulated, at least in part, by the T-helper type 1 (Th1) cytokines IL-2 and IFN-gamma.

T cell receptor-gamma/delta cells protect mice from herpes simplex virus type 1-induced lethal encephalitis.

Increased numbers of T cell receptor (TCR)-gamma/delta cells have been observed in animal models of influenza and sendai virus infections, as well as in patients infected with human immunodeficiency virus and herpes simplex virus type 1 (HSV-1). However, a direct role for TCR-gamma/delta cells in protective immunity for pathogenic viral infection has not been demonstrated. To define the role of TCR-gamma/delta cells in anti-HSV-1 immunity, TCR-alpha-/- mice treated with anti- TCR-gamma/delta monoclonal antibodies or TCR-gamma/delta x TCR-alpha/beta double-deficient mice were infected with HSV-1 by footpad or ocular routes of infection. In both models of HSV-1 infection, TCR-gamma/delta cells limited severe HSV-1-induced epithelial lesions and greatly reduced mortality by preventing the development of lethal viral encephalitis. The observed protection resulted from TCR-gamma/delta cell-mediated arrest of both viral replication and neurovirulence. The demonstration that TCR-gamma/delta cells play an important protective role in murine HSV-1 infections supports their potential contribution to the immune responses in human HSV-1 infection. Thus, this study demonstrates that TCR-gamma/delta cells may play an important regulatory role in human HSV-1 infections.

Proinflammatory functions of IL-2 in herpes simplex virus corneal infection.

Herpes simplex virus type 1 infection of corneas can lead to blinding inflammation in the corneal stroma, which is referred to clinically as herpes stromal keratitis. In our mouse model of this prevalent human disease, a heavy polymorphonuclear neutrophil (PMN) infiltration of the infected cornea leads to progressive tissue destruction. This inflammatory process can be abrogated by in vivo depletion of CD4 T lymphocytes and by neutralization of the cytokines IL-2 and IFN-gamma. The goal of this study was to define the mechanisms by which IL-2 mediates the corneal inflammation. Systemic neutralization of IL-2 after the onset of corneal disease resulted in a rapid regression of inflammation and complete resolution in 50% of the treated mice. The disease remission was associated with loss of IFN-gamma expression in the cornea, as determined by immunohistochemistry, and a significant reduction of IFN-gamma mRNA, as measured by a semiquantitative reverse transcription-PCR analysis. Within 48 h after anti-IL-2 mAb administration, the PMN chemotactic gradient in the infected corneas was abolished, and those PMN that were already present in the central cornea exhibited clear signs of apoptotic cell death. Our results demonstrate that IL-2 mediates corneal inflammation by 1) regulating local IFN-gamma production in an autocrine or a paracrine fashion, 2) establishing a PMN chemotactic gradient, and 3) maintaining PMN viability in the cornea. These results suggest that IL-2 might be targeted for therapeutic intervention in this blinding disease.

Interferon gamma regulates platelet endothelial cell adhesion molecule 1 expression and neutrophil infiltration into herpes simplex virus-infected mouse corneas.

In a mouse model of herpes simplex virus (HSV) 1 corneal infection, tissue destruction results from a CD4+ T cell-mediated chronic inflammation, in which interleukin 2 and interferon (IFN) gamma are requisite inflammatory mediators and polymorphonuclear leukocytes (PMN) are the predominant infiltrating cells. In vivo neutralization of IFN-gamma relieved inflammation at least in part through a specific block of PMN extravasation into HSV-1-infected corneas. Intercellular adhesion molecule (ICAM) 1 and platelet endothelial cell adhesion molecule (PECAM) 1 were upregulated on the vascular endothelium of inflamed corneas. Reduced PMN extravasation in anti-IFN-gamma-treated mice was associated with a dramatic reduction of PECAM-1 but not ICAM-1 expression on vascular endothelium. PMN accumulated in the lumen of corneal vessels after in vivo IFN-gamma neutralization. PECAM-1 was readily detectable on PMN inside the vessels but was not detectable on PMN that extravasated into the infected cornea. Moreover, flow cytometric analysis revealed reduced PECAM-1 expression but elevated major histocompatibility complex class I expression on PMN that recently extravasated into the peritoneal cavity when compared with PMN in the peripheral blood. We conclude that IFN-gamma contributes to HSV-1-induced corneal inflammation by facilitating PMN infiltration; this appears to be accomplished through upregulation of PECAM-1 expression on the vascular endothelium; and PMN downregulate PECAM-1 expression during the process of extravasation.

Ex vivo model of leukocyte migration into herpes simplex virus-infected mouse corneas.

We are investigating neutrophilic infiltration into herpes simplex virus type 1 (HSV-1)-infected mouse corneas. Using a novel ex vivo corneal migration assay, we demonstrated two waves of neutrophil chemotaxis in HSV-1-infected corneas. An early chemotactic gradient developed within 48 h in concert with the appearance of HSV-1 epithelial lesions, peaked by 4 days post-infection (p.i.), and degraded by 6-8 days p.i.. A second chemotactic gradient appeared 10 days after infection, just before the initiation of chronic inflammation. The gradient was maintained in corneas that developed inflammation but rapidly degraded in corneas that failed to develop inflammation. The early chemotactic gradient was established in the absence of T lymphocytes, but the second chemotactic gradient was virtually abrogated by T cell depletion. We conclude that HSV-1 infection induces two temporally separated neutrophil chemotactic gradients in the mouse cornea: an early, transient, T cell-independent gradient; and a later, chronic, T cell-dependent gradient.

Inflammatory infiltration of the trigeminal ganglion after herpes simplex virus type 1 corneal infection.

Following herpes simplex virus type 1 (HSV-1) infection of the cornea, the virus is transmitted to the trigeminal ganglion, where a brief period of virus replication is followed by establishment of a latent infection in neurons. A possible role of the immune system in regulating virus replication and maintaining latency in the sensory neurons has been suggested. We have investigated the phenotype and cytokine pattern of cells that infiltrate the A/J mouse trigeminal ganglion at various times after HSV-1 corneal infection. HSV antigen expression in the trigeminal ganglion (indicative of the viral lytic cycle) increased until day 3 postinfection (p.i.) and then diminished to undetectable levels by day 7 p.i. The period of declining HSV antigen expression. was associated with a marked increase in Mac-1+ cells. These cells did not appear to coexpress the F4/80+ (macrophage) or the CD8+ (T cell) markers, and none showed polymorphonuclear leukocyte morphology, suggesting a possible early infiltration of natural killer cells. There was also a significant increase in the trigeminal ganglion of cells expressing the gamma delta T-cell receptor, and these cells were found almost exclusively in very close association with neurons. This period was also characterized by a rapid and equivalent increase in cells expressing gamma interferon and interleukin-4. The density of the inflammatory infiltrate in the trigeminal ganglion increased until days 12 to 21 p.i., when it was predominated by CD8+, Mac-1+, and tumor necrosis factor-expressing cells, which surrounded many neurons. By day 92 p.i., the inflammatory infiltrate diminished but was heaviest in mice with active periocular skin disease. Our data are consistent with the notion that gamma interferon produced by natural killer cells and/or gamma delta T cells may play an important role in limiting HSV-1 replication in the trigeminal ganglion during the acute stage of infection. In addition, tumor necrosis factor produced by CD8+ T cells and macrophages may function to maintain the virus in a latent state.

Involvement of LFA-1 and ICAM-1 in the herpetic disease resulting from HSV-1 corneal infection.

Herpes simplex virus type 1 (HSV-1) corneal infection in immunologically normal mice results in a transient epithelial lesion followed in about 2 weeks by a potentially blinding inflammatory response in the corneal stroma, and a mild blepharitis. Similarly infected T cell-deficient mice do not develop corneal stromal inflammation, but exhibit severe periocular skin disease and succumb to viral encephalitis. The role of certain adhesion molecules in both T cell activation, and in the extravasation of inflammatory cells from the blood into inflammatory sites is now being established. These studies investigated the involvement of the adhesion pair LFA-1/ICAM-1 in the disease that results from HSV-1 corneal infection in mice. Treatment of mice with mAb to LFA-1 beginning 1 day before HSV-1 corneal infection resulted in a delay in the onset of stromal inflammation, but ultimately stromal inflammation developed to a normal extent. This treatment also caused a significant exacerbation of periocular skin disease, but did not render mice susceptible to encephalitis. Treatment with mAb to ICAM-1 beginning 1 day before HSV-1 corneal infection caused an acceleration of both stromal inflammation and periocular skin disease, and rendered mice uniformly susceptible to lethal encephalitis. Treatment with either mAb beginning 6 days after HSV-1 corneal infection did not significantly affect the clinical course of herpetic disease. Our findings suggest that LFA-1 may play a role in the early phase of corneal stromal inflammation following HSV-1 corneal infection. Both LFA-1 and ICAM-1 appear to be important for protection of the skin from HSV-1 infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Melanin can deplete immunosuppressive substances from the aqueous humor.

Heavily pigmented eyes tend to experience greater inflammation than lightly pigmented eyes following trauma and surgery. The purpose of these studies was to test the possibilities that: (i) melanin augments T cell-responses by depleting or neutralizing anti-inflammatory substances that are normally present in the aqueous humor, and (ii) melanin augments extraocular T cell-mediated inflammatory responses. Two types of experiments were performed. First, the capacity of melanin-adsorbed and non-adsorbed rabbit aqueous humor to inhibit the proliferative response of the T cell line D10.G4.1 to IL-1 was tested. Non-adsorbed aqueous humor inhibited T cell proliferation to the background level in unstimulated cultures, whereas melanin-adsorbed aqueous humor enhanced the proliferation of stimulated, but not resting T cells. Next, mice were sensitized to the antigen conalbumin, and challenged in the ear pinna with conalbumin alone, conalbumin + melanin, or melanin alone and delayed-type hypersensitivity (DTH) was measured. Challenge with melanin alone caused some ear swelling, and melanin increased the DTH response to conalbumin. Our findings are consistent with the notion that melanin can augment intraocular inflammation by depleting or neutralizing the inhibitory components of normal aqueous humor, possibly exposing stimulatory components that are normally masked.

A novel latency-active promoter is contained within the herpes simplex virus type 1 UL flanking repeats.

Herpes simplex virus type 1 (HSV-1) expresses a unique series of RNA molecules, the latency-associated transcripts or LATs, during latent infection of neuronal tissues. Previous studies by others have described a TATA box-containing latency-active promoter, referred to here as LAP1, located approximately 700 bp upstream of the 5' end of the major 2.0-kb LAT. In this report, transient gene expression assays were employed to identify a second, novel latency-active promoter (LAP2) present within a region downstream of LAP1 and 5' proximal to the major 2.0-kb LAT. In contrast to LAP1, this promoter lacks a TATA box but possesses cis-acting regulatory elements and other features frequently observed within eukaryotic housekeeping gene promoters. Unlike most other HSV promoters, LAP2 was down-regulated by the viral transcriptional activators ICP4 and ICP0. The majority of LAP2-positive regulatory elements were located within sequences from -257 to -58 relative to the 5' end of the 2.0-kb LAT, and the basal promoter mapped within sequences from -14 to +28. RNase protection experiments demonstrated that chimeric LAT-chloramphenicol acetyltransferase transcripts produced in the transient assays initiated at or near the 5' end of the major 2-kb LAT. Tn5 insertional mutagenesis of the ICP4 regulatory gene determined that down-regulation of LAP2 required the ICP4 transactivating domain and targeted the minimal promoter region as the site of action by ICP4. Replicating recombinant viruses containing a LAP2-lacZ reporter gene cassette in an ectopic site (glycoprotein C locus) were shown to be active in mouse trigeminal ganglia. Taken together, these experiments suggest that the LAT region of the HSV-1 genome contains at least two latency-active promoters which may play different roles in expressing the various LATs. Alternatively, these promoters may comprise a larger promoter-regulatory complex which may influence transcription during latency.

Herpes simplex virus glycoproteins E and I facilitate cell-to-cell spread in vivo and across junctions of cultured cells.

Herpes simplex virus (HSV) glycoproteins E and I (gE and gI) can act as a receptor for the Fc domain of immunoglobulin G (IgG). To examine the role of HSV IgG Fc receptor in viral pathogenesis, rabbits and mice were infected by the corneal route with HSV gE- or gI- mutants. Wild-type HSV-1 produced large dendritic lesions in the corneal epithelium and subsequent stromal disease leading to viral encephalitis, whereas gE- and gI- mutant viruses produced microscopic punctate or small dendritic lesions in the epithelium and no corneal disease or encephalitis. These differences were not related to the ability of the gE-gI oligomer to bind IgG because the differences were observed before the appearance of anti-HSV IgG and in mice, in which IgG binds to the Fc receptor poorly or not at all. Mutant viruses produced small plaques on monolayers of normal human fibroblasts and epithelial cells. Replication of gE- and gI- mutant viruses in human fibroblasts were normal, and the rates of entry of mutant and wild-type viruses into fibroblasts were similar; however, spread of gE- and gI- mutant viruses from cell to cell was significantly slower than that of wild-type HSV-1. In experiments in which fibroblast monolayers were infected with low multiplicities of virus and multiple rounds of infection occurred, the presence of neutralizing antibodies in the culture medium caused the yields of mutant viruses to drop dramatically, whereas there was a lesser effect on the production of wild-type HSV. It appears that cell-to-cell transmission of wild-type HSV-1 occurs by at least two mechanisms: (i) release of virus from cells and entry of extracellular virus into a neighboring cell and (ii) transfer of virus across cell junctions in a manner resistant to neutralizing antibodies. Our results suggest that gE- and gI- mutants are defective in the latter mechanism of spread, suggesting the possibility that the gE-gI complex facilitates virus transfer across cell junctions, a mode of spread which may predominate in some tissues. It is ironic that the gE-gI complex, usually considered an IgG Fc receptor, may, through its ability to mediate cell-to-cell spread, actually protect HSV from IgG in a manner different than previously thought.

IFN-gamma and IL-2 are protective in the skin but pathologic in the corneas of HSV-1-infected mice.

HSV type 1 (HSV-1) infection of the mouse cornea results in a tissue-destructive inflammatory reaction in the cornea, but little or no disease in the skin surrounding the eye. Depleting T lymphocytes from mice before HSV-1 corneal infection prevents the corneal inflammation but severely exacerbates the periocular skin lesions. Studies described in this communication investigated the role of T cell cytokines in the corneal and periocular skin disease induced by HSV-1 corneal infection. Mice received weekly i.p. injections of rat mAb specific for IL-2, IL-4, or IFN-gamma beginning 1 day before (day -1) or 6 days after (day +6) corneal infection with the RE strain of HSV-1. The severity of corneal inflammation and the area of periocular skin involvement were measured. Treatment with anti-IFN-gamma or anti-IL-2 significantly reduced the incidence and severity of corneal inflammation. Treatment was equally effective when initiated on day -1 (before T cell activation) or day +6 (after T cell activation but before the initiation of corneal inflammation). Treatment with anti-IL-4 had no effect. The histologic features of corneal inflammation in mock-treated mice included neovascularization, corneal edema, and cellular infiltration. Corneas of anti-IL-2-treated mice that developed inflammation had similar but less severe histologic features. Corneas of anti-IFN-gamma-treated mice that developed inflammation had neovascularization and edema but minimal cellular infiltration. Treatment with anti-IFN-gamma or anti-IL-2 significantly exacerbated periocular skin lesions when initiated at day -1, but not when initiated at day +6. Anti-IL-4 treatment had no effect on skin lesions. Treatment with either anti-IFN-gamma or anti-IL-2, when initiated at day -1, significantly inhibited the delayed-type hypersensitivity response to HSV Ag, but when treatment was begun at day +6 only anti-IFN-gamma significantly inhibited the delayed-type hypersensitivity response. Our findings suggest that IFN-gamma and IL-2 are important elements in both an immunopathologic T-lymphocyte response to HSV-1 Ag in the cornea and a protective T lymphocyte response in the skin.

Critical role of corneal Langerhans cells in the CD4- but not CD8-mediated immunopathology in herpes simplex virus-1-infected mouse corneas.

Previous studies have revealed that the RE strain of HSV type 1 (HSV-1) induces a tissue-destructive inflammatory response in the mouse cornea that is mediated by CD4 T lymphocytes, whereas the KOS strain of HSV-1 preferentially activates CD8 T lymphocytes in the cornea. Langerhans cells (LC) normally reside only at the periphery of the cornea but can migrate centripetally after HSV-1 infection. We studied the relative contribution of LC to the corneal inflammation induced by the KOS and RE strains of HSV-1. Ten days after infection, the central one-third of RE HSV-1-infected corneas contained an average of 5.7 LC/high-power field compared with 0.6 LC/high-power field in KOS-infected corneas. We hypothesized that the increased density of LC in RE HSV-1-infected corneas at the time of T lymphocyte infiltration contributed to the preferential activation of CD4 T lymphocytes in these corneas. To test this hypothesis, we gave mice a low dose of UV-B corneal irradiation (150 mJ/cm2) 1 day before infection with HSV-1. UV-B irradiation effectively prevented the migration of LC into the central cornea when measured 10 or 21 days after corneal infection with either HSV-1 strain. UV-B corneal irradiation had no effect on the CTL response to HSV-1 Ag in the regional lymph nodes after corneal infection with KOS or RE HSV-1. The delayed-type hypersensitivity response induced by both strains of virus, when measured 8 and 14 days after corneal infection, was significantly reduced by UV-B irradiation. UV-B irradiation significantly reduced the incidence (p = 0.0023) and severity (p = 0.0008) of corneal stromal disease induced by RE HSV-1 but did not significantly affect the stromal disease induced by KOS HSV-1. To distinguish between the effect of UV-B treatment on the afferent and efferent arms of the Ir in mice, we administered UV-B treatment to one eye, followed 24 h later by RE HSV-1 infection of both eyes. These mice developed a normal delayed-type hypersensitivity response, and stromal inflammation developed normally in the untreated eye. However, stromal inflammation was significantly reduced in the treated eye. Our findings suggest that LC play a critical role in the activation of HSV-reactive CD4 T lymphocytes in the cornea. Moreover, the type of corneal inflammation induced by different strains of HSV-1 may reflect their differential capacity to induce LC migration into the central cornea.