Genetic studies on murine susceptibility to herpes simplex keratitis

A forward phenotypically driven unbiased genetic analysis of host genes that moderate herpes simplex virus virulence and stromal keratitis in mice

Both viral and host genetics affect the outcome of herpes simplex virus type 1 (HSV-1) infection in humans and experimental models. Little is known about specific host gene variants and molecular networks that influence herpetic disease progression, severity, and episodic reactivation. To identify such host gene variants we have initiated a forward genetic analysis using the expanded family of BXD strains, all derived from crosses between C57BL/6J and DBA/2J strains of mice. One parent is highly resistant and one highly susceptible to HSV-1. Both strains have also been fully sequenced, greatly facilitating the search for genetic modifiers that contribute to differences in HSV-1 infection. We monitored diverse disease phenotypes following infection with HSV-1 strain 17syn+ including percent mortality (herpes simplex encephalitis, HSE), body weight loss, severity of herpetic stromal keratitis (HSK), spleen weight, serum neutralizing antibody titers, and viral titers in tear films in BXD strains. A significant quantitative trait locus (QTL) on chromosome (Chr) 16 was found to associate with both percent mortality and HSK severity. Importantly, this QTL maps close to a human QTL and the gene proposed to be associated with the frequency of recurrent herpetic labialis (cold sores). This suggests that a single host locus may influence these seemingly diverse HSV-1 pathogenic phenotypes by as yet unknown mechanisms. Additional suggestive QTLs for percent mortality were identified—one on Chr X that is epistatically associated with that on Chr 16. As would be anticipated the Chr 16 QTL also modulated weight loss, reaching significance in females. A second significant QTL for maximum weight loss in male and female mice was mapped to Chr 12. To our knowledge this is the first report of a host genetic locus that modulates the severity of both herpetic disease in the nervous system and herpetic stromal keratitis.

Interferon gamma is not required for recurrent herpetic stromal keratitis

The role that interferon-gamma (IFNgamma) plays during herpetic stromal keratitis (HSK) has not been definitively determined. In primary HSK most reports suggest that IFNgamma may help control viral replication and contribute to corneal pathology. However, its role in recurrent HSK has not been directly addressed. The present study addresses its role in recurrent HSK by comparing HSK in latently infected normal and IFNgamma gene knockout (GKO) on the C57BL/6 background. We initially evaluated HSK following primary infection and observed that GKO mice had higher tear film virus titers, but virtually identical ocular disease as normal mice. In contrast, following reactivation of latent virus, GKO mice had a greater incidence and severity of opacity, neovascularization, and blepharitis. Interestingly, the incidence of reactivation after UV-B exposure was equivalent in GKO and normal mice, but virus shedding was increased in the GKO groups. We also observed diminished delayed-type hypersensitivity responses in GKO mice, as expected. These data indicate that IFNgamma is important for the control of virus replication in both primary and recurrent ocular HSV infection in C57BL/6 mice. The enhanced recurrent disease seen in GKO mice may be the result of increased viral titers and persistence in these mice which act to prolong the stimulation of an inflammatory response.

Immunoglobulin gene implicated in murine herpes stromal keratitis is not associated with the human disease

PURPOSE

Susceptibility to herpes stromal keratitis (HSK) is strongly influenced by genetic factors, as shown by multiple rodent models using human herpes simplex virus. A single gene, encoding the immunoglobulin G (IgG) 2a heavy chain protein, confers susceptibility or resistance through a mechanism involving molecular mimicry in one mouse model. However, other rodent studies have produced contradictory results. This study tested the hypothesis that the GM23 gene (the human IgG2a homolog) influences susceptibility to HSK in humans.

METHODS

The study population consisted of all consenting patients diagnosed with HSK (25 whites, 2 African Americans) at the Medical University of South Carolina Storm Eye Institute Clinic in Charleston, SC, between August 2000 and June 2004. Healthy controls (23 white adults with no history of HSK) were recruited from the same local population. Genomic DNA from subjects was genotyped at the GM23 locus, which has been implicated as an HSK resistance gene in animal models, by polymerase chain reaction-restriction fragment length polymorphism (RFLP) analysis.

RESULTS

No difference in GM23 genotype frequency was observed between patients with HSK and controls.

CONCLUSION

Susceptibility to HSK in whites is not predicted by GM23 genotype.

The effects of aminoguanidine on primary and recurrent ocular herpes simplex virus infection

In primary ocular herpes simplex virus (HSV) infection, nitric oxide may function to control viral replication and herpetic stromal keratitis (HSK) lesions. Recurrent HSK, manifested as corneal opacity and neovascularization, is the potentially blinding sequel to primary infection. Here, we assess the effects of nitric oxide synthase inhibition on a mouse model of recurrent HSK. In preliminary primary infection experiments, NIH inbred mice treated with aminoguanidine, an inhibitor of inducible nitric oxide synthase (iNOS), experienced no changes in post-infection tear, brain, or ganglia virus titers, but encephalitis-related mortality was elevated. After UV-B stimulated viral reactivation, iNOS inhibition did not affect virus shedding or clinical disease. In contrast to primary HSK, there was no exacerbation of mortality in recurrent disease. Our findings indicate that nitric oxide can be neuroprotective without antiviral effects in primary HSK, and does not play a significant role in the pathogenesis of recurrent HSK. Compared with data from other mouse strains, this work suggests that there may be a genetic component to the importance of NO in controlling ocular HSV infection.

Molecular mimicry versus bystander activation: herpetic stromal keratitis

Herpes stromal keratitis (HSK) is a significant inflammatory disease of the cornea as a result of herpes simplex virus (HSV) infection often progressing to vision loss if left untreated. However, even with immunosuppressive compounds and anti-viral drug treatment, HSV continues to be the leading cause of infectious corneal blindness in the industrialized world. The inflammatory nature of the disease is the root of the pathogenic process characterized by irreversible corneal scarring, neovascularization of the avascular cornea, and infiltration of activated leukocytes. Experimental evidence using mice suggest HSK is the result of either molecular mimicry or a bystander activation phenomenon. This review will revisit the basis of HSK focusing on issues that pertain to the autoimmune component versus collateral damage as a result of non-specific activation as a means to explain the pathologic manifestations of the disease.

Interleukin-10 (IL-10) ameliorates corneal disease in a mouse model of recurrent herpetic keratitis

Interleukin 10 (IL-10), a moderator of Delayed Type Hypersensitivity (DTH) responses, has been demonstrated to be present late in acute HSV corneal infection and may help limit blinding inflammatory lesions there. In contrast, IL-10 is present early in the development of recurrent herpetic stromal keratitis (HSK) lesions in mice. To determine the role of IL-10 and DTH responses in recurrent HSK, we examined DTH responses and disease parameters in latently infected IL-10 knock out (KO) mice, and latently infected normal mice that were untreated or received anti-IL-10 antibodies or recombinant IL-10 following ultraviolet-B stimulated ocular HSV recurrence. Low DTH responses were associated with less severe corneal disease while high DTH responses were associated with greater corneal disease. In IL-10 KO mice, and in normal mice given anti-IL-10 antibodies, corneal opacification was increased and DTH responses were significantly prolonged. Normal mice receiving rIL-10 by ocular and intra-peritoneal routes had less severe corneal lesions. Our results indicate that IL-10 and DTH responses play an important role in the pathogenesis of recurrent HSK in mice.

Identification of equine herpesvirus-1 antigens recognized by cytotoxic T lymphocytes

Equine herpesvirus-1 (EHV-1) causes serious disease in horses throughout the world, despite the frequent use of vaccines. CTLs are thought to be critical for protection from primary and reactivating latent EHV-1 infections. However, the antigen-specificity of EHV-1-specific CTLs is unknown. The aim of this study was to identify EHV-1 genes that encode proteins containing CTL epitopes and to determine their MHC I (or ELA-A in the horse) restriction. Equine dendritic cells, transfected with a series of EHV-1 genes, were used to stimulate autologous CTL precursor populations derived from previously infected horses. Cytotoxicity was subsequently measured against EHV-1-infected PWM lymphoblast targets. Dendritic cells were infected with EHV-1 (positive control) or transfected with plasmids encoding the gB, gC, gD, gE, gH, gI, gL, immediate-early (IE) or early protein of EHV-1 using the PowderJect XR-1 research device. Dendritic cells transfected with the IE gene induced CTL responses in four of six ponies. All four of these ponies shared a common ELA-A3.1 haplotype. Dendritic cells transfected with gC, gD, gI and gL glycoproteins induced CTLs in individual ponies. The cytotoxic activity was ELA-A-restricted, as heterologous targets from ELA-A mismatched ponies were not killed and an MHC I blocking antibody reduced EHV-1-specific killing. This is the first identification of an EHV-1 protein containing ELA-A-restricted CTL epitopes. This assay can now be used to study CTL specificity for EHV-1 proteins in horses with a broad range of ELA-A haplotypes, with the goal of developing a multi-epitope EHV-1 vaccine.

CD4(+) and CD8(+) cells are key participants in the development of recurrent herpetic stromal keratitis in mice

Ocular herpes simplex virus (HSV) infection results in an immune-mediated inflammation of the corneal stroma known as herpetic stromal keratitis (HSK). Recurrent HSK is a common cause of virus-induced corneal blindness in humans. The role of CD4(+) and CD8(+) T cell subsets in the disease pathogenesis is ill defined and varies with the virus strain and host genetic background. To examine the contribution of T cell subsets to corneal disease, we studied the development of recurrent HSK in CD4 or CD8 gene knockout (KO) mice ocularly infected with HSV-1 McKrae strain. Following UV-B induced viral reactivation, corneal opacity in latently infected BALB/c (HSV sensitive) CD4 and CD8 KO mice was reduced compared to infected BALB/c mice with normal genotype. In contrast, opacity in C57BL/6 (HSV resistant) CD4 and CD8 KO latent mice did not differ from genetically normal latent mice. Virus-induced corneal opacity was not demonstrable in C57BL/6 CD4/CD8 double KO mice. Increased viral shedding, measured by reactivation rate, days shedding or viral titers, occurred in CD4 KO mice of both strains. Our findings indicate that both CD4(+) and CD8(+) cells play a role in the immunopathogenesis of recurrent HSK, and their role is dependent upon the host genetic profile.

Mapping of genes involved in murine herpes simplex virus keratitis: identification of genes and their modifiers

Herpes simplex keratitis (HSK) is an inflammatory response to viral infection and self antigens in the cornea and is a major cause of blindness. Using two strains of mice which are susceptible (129/SVEV) and resistant (C57BL/6) to herpes simplex virus (HSV) strain KOS, (129/SVEV x C57BL/6)F(2) mice were generated and examined for their disease susceptibility in terms of clinical symptoms, ocular disease, and antibody production following corneal scarification with HSV (KOS). A genome-wide screen was carried out using microsatellite markers to determine the genetic loci involved in this response. Loci on chromosomes 4, 5, 12, 13, and 14 were shown to be involved in general susceptibility to clinical disease, whereas loci on chromosomes 10 and 17 were shown to be unique to ocular disease.

Therapeutic immunization with a virion host shutoff-defective, replication-incompetent herpes simplex virus type 1 strain limits recurrent herpetic ocular infection

Immunization of mice with herpes simplex virus type 1 (HSV-1) mutant viruses containing deletions in the gene for virion host shutoff (vhs) protein diminishes primary and recurrent corneal infection with wild-type HSV-1. vhs mutant viruses are severely attenuated in vivo but establish latent infections in sensory neurons. A safer HSV-1 mutant vaccine strain, Delta41Delta29, has combined vhs and replication (ICP8-) deficits and protects BALB/c mice against primary corneal infection equivalent to a vhs- strain (BGS41). Here, we tested the hypothesis that Delta41Delta29 can protect as well as BGS41 in a therapeutic setting. Because immune response induction varies with the mouse and virus strains studied, we first determined the effect of prophylactic Delta41Delta29 vaccination on primary ocular infection of NIH inbred mice with HSV-1 McKrae, a model system used to evaluate therapeutic vaccines. In a dose-dependent fashion, prophylactic Delta41Delta29 vaccination decreased postchallenge tear film virus titers and ocular disease incidence and severity while eliciting high levels of HSV-specific antibodies. Adoptive transfer studies demonstrated a dominant role for immune serum and a lesser role for immune cells in mediating prophylactic protection. Therapeutically, vaccination with Delta41Delta29 effectively reduced the incidence of UV-B-induced recurrent virus shedding in latently infected mice. Therapeutic Delta41Delta29 and BGS41 vaccination decreased corneal opacity and delayed-type hypersensitivity responses while elevating antibody titers, compared to controls. These data indicate that replication is not a prerequisite for generation of therapeutic immunity by live HSV mutant virus vaccines and raise the possibility that genetically tailored replication-defective viruses may make effective and safe therapeutic vaccines.

Increased severity of herpes simplex virus type 1-induced keratitis in Hox A5 transgenic mice

PURPOSE

Herpes simplex virus type 1 is a major cause of stromal keratitis and blindness in humans. Understanding of the role of host genes in the pathogenesis of herpes stromal keratitis is limited. We used a transgenic mouse model to examine the effect of a host gene, Hox A5 (which binds to the TAATGARAT sequence in the promoter regions of HSV-1 immediate early genes and increases HSV-1 replication), on the pathogenesis of HSV-1 induced stromal keratitis.

METHODS

Corneas of wildtype and Hox A5 transgenic mice were infected with HSV-1 strain F following corneal scarification. Clinical severity of keratitis was evaluated using slit-lamp biomicroscopy. Histologic severity of keratitis was determined by light microscopic evaluation and by computerized morphometry. Ocular viral replication was measured via plaque assay.

RESULTS

Clinical lesions of stromal keratitis were more severe at 17 and 23 days post infection in Hox A5 transgenic mice than in wildtype mice. Histological evaluation and morphometric analysis confirmed that keratitis lesions were more severe in the transgenic mice. HSV-1 replication was approximately100-fold greater in the corneas of transgenic mice than in wildtype mice.

CONCLUSIONS

Our results demonstrate that a host gene (Hox A5) can increase ocular replication of HSV-1 and alter the pathogenesis of herpetic stromal keratitis.

Analysis of the relationship between viral infection and autoimmune disease

The clinical association between viral infection and onset or exacerbation of autoimmune disorders remains poorly understood. Here, we examine the relative roles of molecular mimicry and nonspecific inflammatory stimuli in progression from infection to autoimmune disease. Murine herpes virus 1 (HSV-1 KOS) infection triggers T cell-dependent autoimmune reactions to corneal tissue. We generated an HSV-1 KOS point mutant containing a single amino acid exchange within the putative mimicry epitope as well as mice expressing a TCR transgene specific for the self-peptide mimic to allow dissection of two pathogenic mechanisms in disease induction. These experiments indicate that viral mimicry is essential for disease induction after low-level viral infection of animals containing limited numbers of autoreactive T cells, while innate immune mechanisms become sufficient to provoke disease in animals containing relatively high numbers of autoreactive T cells.

Incidence and severity of herpetic stromal keratitis: impaired by the depletion of lymph node macrophages

HSV-1 induced stromal keratitis (HSK) is an immune-mediated disease. The role of macrophages in this process is still unclear. In this study we investigated the influence of specific macrophage depletion from the spleen and the submandibular lymph nodes by dichloromethylene diphosphonate liposomes (Cl(2)MDP-LIP) on the course of HSV-1 keratitis. BALB/c mice were infected corneally with 10(5)PFU of HSV-1 (KOS). Groups of mice received Cl(2)MDP-LIP 7 and 2 days prior to infection. Cl(2)MDP-LIP were given by various routes: intravenously (i.v.) for macrophage depletion in the spleen; subcutaneously for macrophage depletion in the submandibular regional lymph node (s.c.); or both i.v. and s.c. The development of HSV-1 keratitis was evaluated clinically and histologically. A standard plaque assay from the infected eyes was used to measure virus clearance. Seventy-nine percent of the HSV-1-infected control mice (n = 14) developed severe stromal keratitis by day 14 p.i. The development of stromal keratitis was inhibited by Cl(2)MDP-LIP given s.c. (64%;n = 14;P < 0.05), i.v. and s.c. (50%;n = 14;P < 0.05), but not by i.v. treatment alone (77%;n = 13). After s.c., i.v. and s.c. Cl(2)MDP-LIP injection, histologically the corneal stroma had a decrease in inflammatory cell infiltration by day 14 p.i. compared to the control group, and the DTH response was reduced. The healing of epithelial HSV-1 keratitis and the virus clearance were not affected significantly. These results indicate an important function of macrophages in the course of HSV-1 keratitis. Virus replication in the eye does not appear to be affected by monocytes/macrophages of lymph nodes and spleen. In contrast, the immunopathological process of stromal HSV-keratitis that results in corneal destruction is profoundly accelerated by macrophages in the lymph nodes.

Pathogenesis of herpes simplex virus type 1-induced corneal inflammation in perforin-deficient mice

Herpetic stromal keratitis (HSK) is an inflammatory disease of the cornea that often results in blindness. It is mediated by a host immune response which is triggered by herpes simplex virus (HSV) infection. Immune effector mechanisms are hypothesized to be important in disease development. We investigated, in a mouse model, whether perforin-dependent cytotoxicity is an important effector mechanism in the production of HSK. Wild-type (C57BL/6) and perforin-deficient (PKO) mice were infected intracorneally with HSV-1 strain F. Clinical disease and histologic lesions of the cornea at 23 days postinfection (p.i.) were significantly less severe in HSV-1-infected PKO mice than in infected wild-type mice. mRNA for the chemokine macrophage inflammatory protein 1alpha (MIP-1alpha) was detected by reverse transcription-PCR in the corneas of infected wild-type mice but not in the corneas of infected PKO mice at 23 days p.i. Adoptive transfer of wild-type HSV-1 immune T-cell-enriched splenocytes into HSV-1-infected PKO mice restored the disease phenotype which was seen in infected wild-type mice. In contrast, mice carrying a null-function mutation in the Fas ligand, which is involved in an alternative cytotoxic mechanism, developed clinical disease and histologic lesions which were comparable to those in wild-type mice. Viral clearance from the eyes of PKO mice was not impaired. There was no significant difference between the infectious viral titers isolated from the eyes of PKO and wild-type mice. Our findings show that perforin is important in the pathogenesis of HSK.

Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

PURPOSE

To describe the most recent advances in our understanding of the cellular and molecular mechanisms involved in the immunopathogenesis of corneal immunoinflammatory disorders including microbial keratitis, peripheral ulcerative keratitis. and allograft rejection.

METHODS

Review of the published peer-reviewed literature that has contributed significantly to our modern understanding of corneal immunology. In addition, the authors have summarized the information in conceptual diagrams that highlight the critical cellular and molecular pathways that lead to corneal immune responses in the two most thoroughly studied corneal immune disorders, herpes simplex keratitis (HSK) and transplant rejection.

RESULTS

In spite of the wide array of molecular and cellular factors that mediate corneal immunity, critical mechanistic facets are shared by the various corneal immunoinflammatory disorders. These include activation and migration of local antigen-presenting cells (APCs), including Langerhans cells (LCs), upregulation in pleiotropic proinflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alfa (TNF-alpha) that can mediate a wide array of immune functions in addition to up-regulating protease expression. and chemokines that play a critical role on the one hand in attracting nonantigen-specific inflammatory cells such as neutrophils and on the other in attracting CD4+ T helper type 1 (Th1) cells that mediate most of the destruction in the cornea.

CONCLUSIONS

In the last 25 years, we have seen our field develop from a descriptive stage into a new phase where the fundamental processes that mediate and effect corneal immunity are being accurately deciphered. It is anticipated that this new knowledge will allow development of specific molecular and genetic therapeutic strategies that could target critical steps in the immunopathogenesis of disease without the untoward side-effects of nonspecific generalized immune suppression that still remains the standard of care today.

Immunopathology of Herpetic Stromal Keratitis: Discordance in CD4+ T Cell Function Between Euthymic Host and Reconstituted SCID Recipients

Infection of the mouse cornea with herpes simplex virus (HSV) results in an immunopathologic disease of the eye termed herpetic stromal keratitis (HSK), in which the principal orchestrator is the CD4+ T cell. The mouse genotype largely determines susceptibility or resistance to HSK. BALB/c mice (H2dIgh-1a) are susceptible, while its congenic C.B-17 strain (H2dIgh-1b), which differs only in the Ig heavy chain locus, is resistant to HSK. As the magnitude and duration of viral replication as well as anti-HSV immune responses were similar in both strains, it was determined whether resistance was due to failure of CD4+ T cells to organize the immunopathologic reaction. Adoptive transfer of HSV-primed or naive CD4+ T cells from resistant C.B-17 strain into HSV-infected SCID mice resulted in HSK lesions indistinguishable from those caused by similar transfers of BALB/c CD4+ T cells. Similar results were obtained with transfers of whole T cell populations as well as with unfractionated splenocytes from the resistant mice. These results show that while intact C.B-17 mice exhibit resistance to HSK, they possess potentially pathogenic CD4+ T cells in their repertoire. The data suggest that the HSV-infected SCID mouse provides a proinflammatory microenvironment that overrides regulatory controls and/or cause activation of quiescent cells into aggressive effector T cells that orchestrate HSK.

Immunity causing blindness: five different paths to herpes stromal keratitis

Herpes stromal keratitis (HSK) is a blinding infectious disease that results from an array of immunopathogenic processes, including herpes simplex virus 1 (HSV-1)-specific T helper 1 (Th1) and Th2 cells, cytotoxic T cells and antibodies. As discussed here by Wayne Streilein and colleagues, strategies designed to prevent and treat this syndrome must be aware of the fact that the disease is multifactorial in its cause and pathogenesis.

Tetrandrine potently inhibits herpes simplex virus type-1-induced keratitis in BALB/c mice

This study investigated the effect of tetrandrine (TDR) on experimental herpes simplex keratitis (HSK) in mice. BALB/c mice were divided as follows: Group 1, untreated; Group 2, acyclovir (ACV)-treated from day 0 postinfection; Group 3, ACV-treated from day 7; Group 4, TDR-treated from day 0; and Group 5, TDR-treated from day 7. All mice were infected in the right cornea with herpes simplex virus (HSV) type I. TDR 30 mg/kg and ACV 120 mg/kg were administered intraperitoneally daily. The mice were observed for 14 days postinfection. Clinical inflammatory reactions and ocular histopathology were analyzed. The herpes specific antibody response and the delayed type hypersensitivity (DTH) response were studied. Of the 22 untreated mice, 16 developed HSK (incidence, 72.7%). TDR given from day 7 reduced the HSK incidence to 8.5% (p < 0.01); the incidence of HSK was 45.4% in mice treated with TDR from day 0 (p > 0.05). Systemic ACV given from day 0 inhibited HSK development (p < 0.01); ACV given from day 7 resulted in an HSK incidence of 50% (p > 0.05). The specific anti-HSV antibody response in the serum of mice treated with TDR or ACV either from day 0 or day 7 was significantly less than that of untreated mice (p < 0.01 and p < 0.05, respectively), and TDR treatment suppressed DTH responses to HSV (p < 0.05). Systemic TDR administered after HSV inoculation of the cornea significantly modulates murine HSK development at least partly by modifying the host immune/inflammatory response to the virus.

T cell receptor V beta gene expression in experimental herpes stromal keratitis

Our study examined T cell receptor (TCR) V beta mRNA expression in a murine model of experimental herpes simplex keratitis (HSK). We employed a polymerase chain reaction (PCR) technique to detect TCR V beta mRNA expression in the inoculated eyes of both HSK-susceptible and HSK-resistant mice at different time points after corneal inoculation with herpes simplex virus type 1 (HSV-1), followed by Southern blotting and densitometry analysis. In eyes from HSK-susceptible C.AL-20 mice, a more diverse TCR V beta transcript usage pattern was detected as compared with that seen in HSK-resistant C.B-17 mice. V beta 8 family members were expressed in both strains of mice at days 11, 14 and 21 post-inoculation. By densitometry, at day 11, the intensity of expression of V beta 8.2 and V beta 8.3 message was significantly greater in the eyes of C.AL-20 mice; V beta 8.1 was expressed only in C.B-17 mice. There were obvious differences in the TCR V beta expression between HSK-susceptible and HSK-resistant mice. The differences in the intensity of the message expressed by V beta 8 family members between the two strains could be correlated to previous experiments that showed V beta 8.1,2+ T cells as the main infiltrating cells in the corneas of HSK-susceptible mice by day 11 and 14 after challenge with HSV-1.

Resistance to herpes stromal keratitis conferred by an IgG2a-derived peptide

Not all peripheral tissue antigens enter the thymus and it is unclear how the immune system remains tolerant to this class of self antigen. As tolerance to self peptides can generate gaps in the T-cell repertoire for cross-reactive foreign antigens, we investigated whether this mechanism might also diminish autoimmune reactions to similar peptides expressed by peripheral tissues. Herpes stromal keratitis (HSK) is a virally induced autoimmune reaction against corneal tissues mediated by T cells, and is a leading cause of human blindness. Resistance to HSK in mice is associated with allotypic variation in immunoglobulin genes, possibly because circulating immunoglobin-derived peptides can cross-tolerize T cells specific for corneal tissue autoantigens. Here we show that HSK is mediated by T-cell clones specific for corneal self antigens which also recognize an allotype-bearing peptide derived from IgG2a, and that exposure of HSK-susceptible mice to a soluble form of this peptide confers resistance to HSK. Shared expression of peptide subsequences between sequestered tissue proteins and circulating proteins may be important for maintenance of self-tolerance and prevention of autoimmunity.

Immunisation against HSV-1 keratitis with a synthetic gD peptide

The authors tested the protective efficacy of, and the immune response to, immunisation with a synthetic peptide of glycoprotein D (gD) of HSV-1 in a murine model of herpes stromal keratitis (HSK). HSV-1 susceptible A/J mice were immunised subcutaneously with a peptide corresponding to the N-terminal epitope gD(5-23) prior to corneal HSV-1 challenge. Divergent immunisation protocols were compared for their protective potency, their ability to prevent the establishment of latency in the trigeminal ganglion, and their effect on the immune system. Low dosages (31 micrograms) of gD(5-23) protected against encephalitis and HSK. Protective efficacy was higher when gD(5-23) was coupled to the carrier protein keyhole limpet haemocyanin (KLH) and was emulsified with adjuvant. Latent infection was found in all control mice but in only 50-75% of immunised mice. The most potent protection was correlated with anti-HSV-1 neutralising antibodies of IgG1 and IgG2a isotypes, but free gD(5-23) protected in the absence of anti-HSV-1 antibodies. Our results suggest that immunisation with gD(5-23) stimulates both humoral and cellular immune mechanisms which protect against HSV-1 keratitis.

CD4+V beta 8+ T cells mediate herpes stromal keratitis

T lymphocytes are critical in mediating herpes simplex stromal keratitis (HSK). Using immunohistologic methods, we studied the T cell subsets and the T cell receptor variable region (TCR V beta) repertoire of T cells in the eye after corneal infection with HSV (KOS strain). We investigated the possibility that there might be differential V beta preferential usage in HSK resistant and susceptible BALB/c congenic mice that differ only in a small region associated with the Igh-1 gene locus. The inflamed corneas of HSK susceptible C.AL-20 mice were mainly infiltrated by CD4+ cells and by V beta 8 expressing cells. Such T cells were not seen in the corneas of resistant C.B-17 mice. Our results indicate that CD4+V beta 8+ cells are involved in mediating HSV-1 stromal keratitis.

The role of natural killer cells in the development of herpes simplex virus type 1 induced stromal keratitis in mice

Natural killer (NK) cells and acquired cell-mediated immunity effector cells (delayed type hypersensitivity (DTH) and cytotoxic T lymphocytes (CTL)) have been reported to play a vital role in the defence of the host against tumour and viral infections in locations other than the eye. A vigorous cellular inflammatory response to viral infections of the cornea, however, with the attendant damage to the corneal clarity, has obvious evolutionary disadvantages, and a substantial body of evidence indicates that in animals (e.g. mice) which are highly susceptible to inflammatory destruction of the cornea following corneal encounter with herpes simplex virus, it is the animal's immunological/inflammatory response which is responsible for the corneal damage. We examined the role of natural killer cells in the development of herpes stromal keratitis (HSK) in NK-deficient (C57BL/6J-bgj (beige)) mice and their NK-competent (C57BL/6J (black) relatives. The beige (NK-deficient) mice were just as resistant to HSK as were the black mice. We also studied the effects of NK cell depletion of BALB/c Igh-1 disparate congenic mice. C.AL-20 (Igh-1d) mice are ordinarily highly susceptible to necrotising HSK. In vivo NK-cell depletion in these mice significantly decreased the incidence and severity of HSK in these animals (p < 0.0005). Corneas from untreated C.AL-20 mice contained T cells, macrophages and NK cells. The corneal infiltrate from NK-depleted C.AL-20 mice consisted of T cells and macrophages but no NK cells. These data indicate that NK cells are participants in the development of HSK in the murine model of this disease.

Immunization with replication-defective mutants of herpes simplex virus type 1: sites of immune intervention in pathogenesis of challenge virus infection

Replication-defective mutants of herpes simplex virus type 1 (HSV-1) were used as a new means to immunize mice against HSV-1-mediated ocular infection and disease. The effects of the induced immune responses on pathogenesis of acute and latent infection by challenge virus were investigated after corneal inoculation of immunized mice with virulent HSV-1. A single subcutaneous injection of replication-defective mutant virus protected mice against development of encephalitis and keratitis. Replication of the challenge virus at the initial site of infection was lower in mice immunized with attenuated, wild-type parental virus (KOS1.1) or replication-defective mutant virus than in mice immunized with uninfected cell extract or UV-inactivated wild-type virus. Significantly, latent infection in the trigeminal ganglia was reduced in mice given one immunization with replication-defective mutant virus and was completely prevented by two immunizations. Acute replication in the trigeminal ganglia was also prevented in mice immunized twice with wild-type or mutant virus. The level of protection against infection and disease generated by immunization with replication-defective mutant viruses was comparable to that of infectious wild-type virus in all cases. In addition, T-cell proliferative and neutralizing antibody responses following immunization and corneal challenge were of similar strength in mice immunized with replication-defective mutant viruses or with wild-type virus. Thus, protein expression by forms of HSV-1 capable of only partially completing the replication cycle can induce an immune response in mice that efficiently decreases primary replication of virulent challenge virus, interferes with acute and latent infection of the nervous system, and inhibits the development of both keratitis and systemic neurologic disease.

The role of Igh-1 disparate congenic mouse T lymphocytes in the pathogenesis of herpetic stromal keratitis

The corneal destruction associated with herpes simplex keratitis (HSK) is primarily the result of the host's immune response to herpes simplex virus type-1 (HSV-1) infection. We examined the role of T cells and T cell subsets in the pathogenesis of HSK. Naive and immune T cells and HSV-1 immune CD4+ and CD8+ subsets from Igh-1 disparate BALB/c congenic mice were adoptively transferred into athymic BALB/c nude mice, which normally do not develop HSK. The results demonstrated that while the transfer of naive T cells from either HSK-susceptible C.AL-20 (Igh-1d) or HSK-resistant C.B-17 (Igh-1b) mice had little influence on HSK development, transfer of either CD3+ or CD4+ HSV-1 immune T cells from C.AL-20 mice resulted in the development of severe HSK in all of the recipients. Transfer of the same cell populations from C.B-17 mice resulted in the development of only a mild keratitis in 50% of the recipients. Transfer of CD8+ cells from either donor strain did not result in stromal disease in any recipient mouse. These results clearly demonstrate the pivotal role of CD4+ T cells in the development of necrotizing herpes stromal keratitis, and further demonstrate that CD8+ T cells are not essential in HSK development in the BALB/c system.

Herpetic stromal keratitis in the reconstituted scid mouse model

Infections of the cornea with herpes simplex virus type 1 cause inflammatory lesions which frequently lead to blindness. The disease is suspected to be immunopathological in nature. To establish this point and to study possible mechanisms involved, corneal infections in C.B-17 scid/scid and cell-reconstituted scid mice were investigated. Whereas unreconstituted scid mice failed to develop herpetic stromal keratitis (HSK) and died of encephalitis, mice reconstituted with T lymphocytes generated severe lesions. T cells of the CD4+ subset were found to be essential mediators of the HSK lesion, while T cells of the CD8+ subset protected mice from lethality. The results confirm that HSK is an immunopathological disease and that scid mice provide a convenient model that should prove valuable in establishing the biochemical mechanisms by which HSK is mediated.

Herpes simplex keratitis: role of viral infection versus immune response

The cumulative clinical and experimental data regarding the role of viral infection versus the immune response in the pathogenesis of herpes simplex stromal keratitis and central disciform endotheliitis are discussed. Ultrastructural and viral isolation studies have been performed in only a limited number of cases of human stromal keratitis and disciform endotheliitis. Virus has been isolated from the minority of corneas cultured, whereas viral particles have been demonstrated in selected cases of stromal keratitis, most of which had been treated with steroids at some point in time. The possibility of corneal latency in cases of quiescent herpetic stromal keratitis will require further systematic study. Review of the experimental and clinical findings suggests a dialectical role of the immune response in limiting viral infection, while contributing to corneal opacification and scar formation.

Immunomodulation of experimental murine herpes simplex keratitis: II. Glycoprotein D protection

Subcutaneous immunization with purified HSV-1 glycoprotein D (gD) protects susceptible A/J mice against keratitis and encephalitis following corneal HSV-1 challenge. Mice were immunized with gD, in complete Freund's adjuvant, 3.0 micrograms/mouse followed by two booster doses of 1.5 micrograms/mouse at weeks 2 and 4. Control groups of A/J mice were injected with either complete Freund's adjuvant (unimmunized controls) or live HSV-1 MP strain (immunized controls). All mice were challenged ocularly at week 5 with HSV-1, F strain (6.5 x 10(3) PFU) after corneal scarification. None of the 16 animals immunized with gD developed stromal keratitis; only 3 out of 12 animals immunized with live HSV-1 developed a stromal keratitis; 13 out of 16 CFA primed unimmunized mice developed severe stromal keratitis within 14 days post corneal challenge, and 3 out of 16 control CFA primed animals died within 16 days post corneal challenge. At the time of sacrifice (3 weeks post corneal challenge), the ipsilateral trigeminal ganglia were removed and assayed for latent HSV-1 using cocultivation on Vero cell monolayers. The results of these experiments indicate that immunization with gD produces protection against latent ganglionic infection in 56% of the immunized animals, and provides protection against keratitis and death following HSV corneal challenge.

Immunomodulation of experimental murine herpes simplex keratitis: I. UV-HSV protection

A/J mice were immunized subcutaneously with ultraviolet light (UV) inactivated herpes simplex virus type-1, MP strain (HSV-MP). Control A/J mice were immunized subcutaneously either with media (unimmunized controls) or with live HSV-MP (immunized controls). Immunized and control mice were challenged ocularly with either MP or mP strain HSV-1 after corneal scarification and were followed for 3 weeks post corneal challenge. The mice were observed during this time period for signs of herpes simplex keratitis (HSK), lid lesions and encephalitis. At the time of sacrifice, the ipsilateral trigeminal ganglia were removed and assayed for latent HSV-1 using cocultivation on Vero cell monolayers. The results of these studies demonstrated that immunization with UV inactivated HSV (UV-HSV) gave the same protection against keratitis and encephalitis as immunization with live virus. Furthermore, the cocultivation assays indicated that immunization with either live HSV-1 or UV inactivated HSV-1 protected against the establishment of latency.

Passive transfer of anti-HSV-1 IgG protects against stromal keratitis in mice

Cellular immune mechanisms are felt to play a primary role in modulating responses to herpes simplex virus (HSV) infections, but the role of anti-HSV antibody is less clear. We first investigated the effects of passive transfer of murine serum containing anti-HSV antibody and then fractionated IgG subclasses on the development of HSV stromal keratitis in mice. Both immune sera and fractionated IgG's from these sera were effective in preventing stromal keratitis in susceptible mice. Non-IgG immunoglobulins and other serum proteins are unnecessary and inadequate in transferring protection; transfer of sera depleted of IgG had no influence on the development of keratitis. These results suggest an important role for anti-HSV antibody in modulating destructive corneal responses to HSV.

Herpes simplex virus type 1 induces anterior chamber-associated immune deviation (ACAID) in mouse strains resistant to intraocular infection

Inoculation of herpes simplex virus Type 1 into the anterior chamber of BALB/c mice induces a characteristic ocular infection involving primarily the anterior segment of virus-injected eyes and the retina of contralateral uninjected eyes. In the BALB/c strain, which is susceptible to herpetic retinitis, anti-HSV delayed hypersensitivity responses are actively suppressed, although anti-HSV antibody responses remain intact. We previously demonstrated that C57B1/6 mice, as well as (BALB/c X C57B1/6) F1 are highly resistant to HSV-1 retinitis. Studies have now been performed to determine the relationship between systemic immune responses to HSV and the resistance of C57B1/6 and the (BALB/c X C57B1/6) F1 to develop retinitis after inoculation of HSV into one anterior chamber. Despite the resistance to herpetic retinitis by B6 and F1 mice, both strains developed a pattern of systemic immune responses to HSV similar to those observed in the susceptible BALB/c mice. Therefore, resistance to retinal infection with HSV-1 does not appear to correlate with the pattern of systemic cell-mediated or humoral immune responses to intracameral HSV-1.