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.     

Improvement of HSV-1 necrotizing keratitis with amniotic membrane transplantation

PURPOSE: Stromal herpes simplex virus keratitis (HSK) is an immune-mediated disease. Previous studies have indicated that T cells, neutrophils, and macrophages contribute to the tissue damage in HSK. It has been shown that human amniotic membrane promotes epithelial wound healing and has diverse anti-inflammatory effects. In this study, the effect of amniotic membrane transplantation (AMT) on corneal wound healing and on inflammation in mice with necrotizing HSK was examined. METHODS: BALB/c mice were corneally infected with 10(5) plaque-forming units (PFU) of HSV-1 (KOS strain). In 16 mice that exhibited severe ulcerating HSK, the cornea was covered with a preserved human amniotic membrane as a patch. Corneas in 16 infected mice remained uncovered and served as a control. On days 2 and 7 after surgery, the amniotic membrane was removed (eight mice in each group), the HSV-1-infected cornea was evaluated clinically, and the eye was enucleated. Tissue sections were analyzed histologically for epithelialization and cellular infiltration and immunohistochemically with anti-CD3 mAb to T cells, anti-CD11b mAb to both macrophages and neutrophils, or anti-F4/80 mAb to macrophages. RESULTS: Profound regression of corneal inflammation and rapid closure of epithelial defects were observed clinically within 2 days in the amniotic membrane-covered eyes, whereas HSV-1 keratitis and ulceration progressed in all mice in the control group (P < 0.001). Histologically, corneal edema and inflammatory infiltration, and immunohistochemically the number of CD3(+), CD11b(+), and F4/80(+) cells in the cornea were markedly decreased at 2 and 7 days after amniotic membrane application, compared with the uncovered control corneas (P < 0.001). CONCLUSIONS: AMT promotes rapid epithelialization and reduces stromal inflammation and ulceration in HSV-1 keratitis. AMT in mice with HSV necrotizing stromal keratitis appears to be a useful model for investigating the effect and the action mechanism of human amniotic membrane.     

OX40-Ig融合蛋白对鼠单纯疱疹性角膜基质炎的抑制作用

目的研究OX40-Ig融合蛋白对鼠单纯疱疹性角膜基质炎(HSK)的免疫抑制作用。方法将1×106PFU的单纯疱疹病毒1型(HSV-1)Mckrae毒株接种于BALB/c鼠的角膜上建立HSK模型;分别于接种病毒的当天、接种后第2、4d将OX40-Ig融合蛋白100μg注射到鼠的腹膜下,观察OX40-Ig融合蛋白对鼠HSK的影响。结果OX40-Ig融合蛋白使鼠外周血中CD4 T细胞减少了78·2%,使鼠HSK发病率由83·3%下降到20·0%。OX40-Ig治疗组的小鼠角膜基质混浊程度较对照组明显减轻,角膜内炎性细胞浸润也明显减少,迟发型超敏反应能力显著下降。结论OX40-Ig融合蛋白能够阻断OX-40/OX-40L协同刺激途径,抑制CD4 T细胞增生,阻止HSK的发病,减轻HSK的严重程度。     

Influence of dimethylfumarate on experimental HSV-1 necrotizing keratitis

Background This study was performed to investigate the influence of fumaric acid esters on the course of herpes stromal keratitis (HSK).Methods The corneas of BALB/c mice were inoculated with 105 plaque-forming units of herpes simplex virus 1 (HSV-1, KOS strain). Groups of mice were treated intraperitoneally with phosphate buffered saline (PBS) (control mice), or with dimethylfumarate (DMF) at 15 mg/kg of body weight dissolved in PBS daily for 28 days pre-infection and for 14 days post-infection. The course of HSV-1 keratitis was studied clinically. Corneal sections were examined for inflammatory cell infiltration. The numbers of CD3, GR-1, CD11b and F4/80-expressing cells infiltrating the corneas were analyzed by immunohistochemistry.Results On day 14 after HSV infection, 72% of the mice in the control group had severe HSK. The development of HSK was reduced by DMF treatment in the DMF group (22%) (P=0.004). The total number of inflammatory cells and infiltration of polymorphonuclear-neutrophils (PMNs) were reduced in the corneas of DMF-treated mice. Compared to the PBS-treated mice, numbers of CD3, CD11b, GR-1 and F4/80-positive cells were reduced in the DMF group of mice.Conclusions The course of experimental herpes stromal keratitis can be improved with systemic fumaric acid ester treatment. The improvement of keratitis correlates with a reduced corneal infiltration of T cells and mononuclear cells.The authors have no financial interest in any of the reagents used in this study     

Herpes simplex virus-specific T cells infiltrate the cornea of patients with herpetic stromal keratitis: no evidence for autoreactive T cells

PURPOSE: Herpetic stromal keratitis (HSK) is a T-cell-mediated inflammatory disease initiated by a herpes simplex virus (HSV) infection of the cornea. Recently, studies in the HSK mouse model have shown that the immunopathogenic T cells are directed against the HSV protein UL6 cross-reacting with an unknown corneal autoantigen. Whether this type of autoimmunity plays a role in human HSK was analyzed. METHODS: T-cell lines (TCLs) were generated from corneal buttons of 12 patients with different clinical stages of HSV-induced necrotizing stromal keratitis (n = 9) or immune stromal keratitis (n = 3). The initiating virus was identified by polymerase chain reaction and immunohistology performed on the corneal buttons. Peripheral blood mononuclear cells (PBMCs) were isolated, and B cell lines (BLCLs) were generated by transformation with Epstein-Barr virus. Proliferative responses of these intracorneal TCLs were determined by culturing T cells with autologous BLCLs infected with HSV-1, HSV-2, wild-type vaccinia virus (VV-WT), or VV expressing HSV-1 UL6 (rVV-UL6). Alternatively, T cells were incubated with PBMCs pulsed with human cornea protein extract. RESULTS: Irrespective of clinical diagnosis or treatment, T cells were recovered from the corneal buttons of all the 12 HSK patients. The intracorneal TCLs of 9 of the 12 HSK patients showed HSV-specific T-cell reactivity. In none of the TCLs, T-cell reactivity against HSV-1 UL6 or human corneal antigens was detected. CONCLUSIONS: These data suggest that the potentially immunopathogenic intracorneal T-cell response in HSK patients is directed to the initiating virus and not to a human corneal autoantigen or HSV-1 UL6.     

单纯疱疹病毒性角膜炎小鼠模型的建立及鉴定

目的：探讨建立不同感染时期HSK小鼠动物模型,为HSK的深入研究建立基础。方法：Balb/c小鼠125只麻醉后在显微镜下用刀片背面尖端于角膜＂#＂字划痕,其中100只小鼠接种HSV-Ⅰ病毒,另25只小鼠不接种病毒作为正常对照组。术后每天用10g/L荧光素钠染色后裂隙灯显微镜下观察角膜病变发生情况,并取角膜表面泪液进行HEK293T细胞检测以确定裂隙灯显微镜下有无病毒复制。对潜伏感染期小鼠模型采用紫外线B光照射以诱导HSK复发。结果：接种HSV-Ⅰ病毒的小鼠模型眼于接种后3d内全部出现急性上皮性角膜炎表现。经阿昔洛韦滴眼液治疗1wk后角膜炎症消失,但角膜和三叉神经节中PCR检测病毒仍为阳性。潜伏感染期小鼠模型经紫外线B光照射后也都在1wk内复发,并表现为以基质型角膜炎为主要临床表现的角膜病变。结论：采用角膜划痕法对Balb/c小鼠接种HSV-Ⅰ病毒和紫外线B光照射可以成功地制作出原发感染期、潜伏感染期和复发感染期等不同感染时期的HSK模型,而且操作相对简单、方便易行。     

Effect of NF-κB Inhibitor PDTC on a Herpetic Stromal Keratitis Mouse Model

 Purpose: To investigate the effect of NF-κB inhibitor PDTC on inflammation response in mice with herpetic stromal keratitis (HSK). Methods: A total of 120 female BALB/c mice aged 4-6weeks were treated by scuffing the epithelium of the right cornea with the pinhead of 30G syringe, and approximately 1 ×106PFU of HSV-1virus was seeded onto the corneal surface.  The eye was then exposed to 170mJ/cm2 of UV light 7 weeks later, in order to induce the relapse of HSK. PDTC eye drops adjusted to various concentrations (0.1mg/ml, 1.0mg/ml and 10mg/ml ) with PBS, PBS only was used on control animals. All animals received PDTC or PBS eye drops 6 times/day, 1 drop/time for 7 consecutive days. Mice were sacrificed: 8h, 1d, 3d and 7d after administration. Corneal tissues were prepared for the detection of IL-1β, IL-4, IL-6 and IL-12 by ELISA and histological study. Results: Neutrophilic leukocytes and lymphocytes were found in the cornea of HSK mice. ELISA results showed fluctuated expressions of IL-1β, IL-4, IL-6 and IL-12. IL-1β and IL-4 of high dose group was significantly lower than that of control group (P<0.05), while IL-6 and IL-12 of high dose group was significantly higher than that of control group (P<0.05). Conclusion: A high concentration of PDTC can suppress certain inflammatory factors in HSK mice while improve the expression of others.     

Topical treatment with antisense oligonucleotides targeting tumor necrosis factor-alpha in herpetic stromal keratitis

PURPOSE: Tumor necrosis factor (TNF)-alpha is a pleiotropic factor that is critical for the development of inflammation. The authors investigated whether topical application of TNF-alpha-antagonizing molecules, antisense oligonucleotides (ASON), might be an effective way of modifying the course of immune-mediated herpetic stromal keratitis (HSK). METHODS: ASON targeting TNF-alpha mRNA were examined for their efficiency in interfering with the production of this cytokine in vitro. In vivo uptake was determined by FITC-labeled ASON. HSV-1 corneally infected mice were injected three times with ASON. Mice from the control groups received unrelated control oligonucleotides (CON) or buffer. The clinical course of HSK, the delayed-type hypersensitivity (DTH) reaction, the uptake of [(3)H]thymidine from cells derived from the spleen, virus-neutralizing antibody titers in the serum, and viral replication in the infected eyes were determined. The eyes were examined histologically. The corneal TNF-alpha content was measured by ELISA. RESULTS: The TNF-alpha ASON reduced the lymphocytic cytokine expression in vitro. In vivo, the FITC-labeled molecules were detected in the cornea even after 10 days. In the TNF-alpha ASON mice the incidence of HSK decreased, and the severity of the disease was diminished. The corneal content of TNF-alpha was reduced, and the number of inflammatory cells was decreased. The other investigated parameters were not significantly altered by TNF-alpha ASON treatment. CONCLUSIONS: The data suggest that TNF-alpha ASON diminishes the release of TNF-alpha from cultured lymphocytes and from lymphocytes in the HSV-1-infected cornea. This topical treatment mitigates the course of HSK, whereas the systemic antiviral effector functions were not impaired.     

Macrophage depletion inhibits experimental choroidal neovascularization

OBJECTIVE: To investigate the role of macrophages in the development of laser-induced choroidal neovascularization (CNV) by selective depletion with liposomal clodronate (Cl(2)MDP-LIP). METHODS: Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice. Animals were treated with intravenous (IV) and/or subconjunctival (SC) Cl(2)MDP-LIP or PBS-LIP at the following time points: 2 days before, immediately after, 2 days before and immediately after, or 2 days after laser injury. CNV responses were compared on the basis of en masse volumetric measurements and fluorescein angiography after laser photocoagulation. Macrophages were identified by immunostaining for F4/80, and vascular endothelial growth factor (VEGF) expression was quantified by ELISA. RESULTS: Macrophages invaded the site of laser injury within 1 day of photocoagulation and peaked at 3 days. IV Cl(2)MDP-LIP significantly decreased the volume of CNV and angiographic leakage when administered 2 days before and/or immediately after laser injury, but not when administered 2 days after injury. SC Cl(2)MDP-LIP significantly decreased lesion volume when coadministered with IV PBS-LIP but not IV Cl(2)MDP-LIP. IV Cl(2)MDP-LIP was significantly more beneficial when administered 2 days before laser injury than immediately after, but combining SC Cl(2)MDP-LIP with IV treatment eliminated this difference. Reduction in CNV volume correlated with VEGF protein levels and number of infiltrating macrophages. CONCLUSIONS: Generalized macrophage depletion reduced the size and leakage of laser-induced CNV and was associated with decreased macrophage infiltration and VEGF protein. These findings define the role of the macrophage as a critical component in initiating the laser-induced CNV response.     

Amniotic membrane transplantation improves herpetic keratitis by local and not by systemic effects

PURPOSE: The immune mediated HSV-1 stromal keratitis (HSK) rapidly improves after amniotic membrane transplantation (AMT). This study investigated whether AMT modulates the T cell response and whether the anti-inflammatory action of AMT is due to local or systemic effects. METHODS: Corneas of BALB/c mice were infected with 10(5) (PFU) of HSV-1. Animals with ulcerating keratitis on day 14 post-infection were divided into 4 groups: group 1 ( n=12): right eye AMT;group 2 ( n=12): right eye tarsorrhaphy; group 3 ( n=8): right eye tarsorrhaphy, left eye AMT;group 4 ( n=8): both eyes tarsorrhaphy.The mice were examined for clinical signs of HSV keratitis after 2 days. Corneal sections were studied histologically and the inflammatory cell infiltration was studied by immunohistochemical staining. DTH response and the HSV-specific 3H-thymidin-uptake were compared between the groups. RESULTS: Compared to group 2, ulceration and stromal inflammation was profoundly improved in group 1 ( p<0.01).The corneas in the AMT mice had fewer inflammatory cells, CD3+,CD4+ and CD8+ cells than the control mice ( p<0.01).There were no significant differences between groups 1 and 2 with respect to the delayed type hypersensitivity reaction (DTH response) and the HSV-specific 3H-thymidin uptake. AMT or tarsorrhaphy on the left eyes in groups 3 and 4 had no influence on the course of keratitis or the T cell response. CONCLUSIONS: Ulcerating herpetic keratitis markedly improves after AMT. Our observations indicate that this is caused predominantly by local and not by systemic AMT-related effects.     

Transplantation of amniotic membrane in murine herpes stromal keratitis modulates matrix metalloproteinases in the cornea

PURPOSE: To study matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) in the corneas from mice with ulcerative herpes stromal keratitis (HSK) treated with amniotic membrane transplantation (AMT). METHODS: The corneas from BALB/c mice were infected with HSV-1. Mice with ulcerative HSK on postinfection (PI) day 14 were used for the experiments. In one group of mice, the corneas were treated with transplantation of amniotic membrane (AMT) that was secured with a tarsorrhaphy, and a control group underwent tarsorrhaphy alone. After 2 days, the appearance of corneal ulcers and stromal inflammation was judged clinically. Corneal sections were studied by immunohistochemistry for the expression of MMP-2, -8, and -9 and TIMP-1 and -2. MMP activity in the corneas was investigated by zymography, and the expression of the enzymes was measured by the Western blot technique. RESULTS: At day 14 PI, the ulcers stained intensely positive for MMP-2, -8, and -9 and TIMP-1 and -2. Ulceration (P < 0.001), stromal inflammation (P < 0.01) and inflammatory cell infiltration (P < 0.001) markedly improved by day 2 after AMT. This was associated with reduced expression (P < 0.01) and activity of MMP-8, and -9 and increased localization of TIMP-1 (P < 0.01), whereas TIMP-2 was not affected. In contrast, high levels of expression of MMP-8 and -9 remained in the cornea after tarsorrhaphy, and the TIMP-1 expression was only slightly upregulated. CONCLUSIONS: Rapid improvement of HSV-1-induced ulcerative keratitis is noted after amniotic membrane transplantation. This may be caused by reduced expression and activity of MMP-8 and -9, increased expression of TIMP-1, and sustained expression of TIMP-2.     

白细胞介素10对小鼠单纯疱疹性角膜基质炎作用的实验研究

研究白细胞介素10(IL-10)在小鼠单纯疱疹性角膜基质炎(herpetic stromal keratitis,HSK)中的作用。方法雌性BALB／c小鼠80只分为2组,每组40只;将单纯疱疹病毒1型接种于小鼠角膜上建立HSK动物模型;分别于鼠角膜接种病毒前的6h、当日及接种后2、4d,向实验组鼠的角膜内注射重组IL-10 20ng,腹腔内注射鼠重组IL-10 500 ng;对照组同步注射生理盐水;观察IL-10对小鼠HSK的发病率、临床特征、角膜病毒滴度、角膜细胞因子含量、角膜病理改变及迟发型超敏反应(DTH)的影响。结果IL-10降低了HSK发病率,减轻了HSK角膜混浊程度、角膜新生血管化程度及角膜内炎性细胞浸润,降低了角膜内IL-2和IL-6的含量,抑制了鼠的DTH反应。IL-10不影响病毒在角膜内的复制和清除。结论IL-10可抑制鼠的DTH反应和HSK的发病进展。     

CD8 T cells mediate transient herpes stromal keratitis in CD4-deficient mice

PURPOSE: To evaluate the role of CD4(+) T cells in the development of murine herpes stromal keratitis (HSK). METHODS: The corneas of wild-type (WT) BALB/c mice and three types of CD4-deficient BALB/c mice (CD4(-/-), CD4-depleted, CD4 and CD8 double-depleted) were infected with different doses of HSV-1 RE, and HSK incidence and severity were monitored. Corneal infiltrates were quantitatively and functionally assayed by flow cytometric analysis of individually digested diseased corneas and documented histologically. RESULTS: At a relatively high infectious dose (1 x 10(5) pfu/cornea): (1) CD4-deficient and WT BALB/c mice had severe HSK with a similar incidence (80%-100%), whereas HSK did not develop in mice deficient in both CD4(+) and CD8(+) T cells; (2) neutrophils were the predominate leukocyte in the corneas of CD4-deficient and WT mice; (3) the corneas of WT mice had activated, HSV-1-specific CD4(+) T cells, but few if any CD8(+) T cells; (4) the corneas of CD4-deficient mice had activated, HSV-1-specific CD8(+) T cells; and (5) HSK in CD4-deficient mice was transient, showing loss of CD8(+) T cells at 2 to 3 weeks after infection (pi) followed by a loss of neutrophils. At a relatively low infectious dose of HSV-1 (10(3) pfu/cornea) severe HSK developed in 80% to 90% of WT mice, but in only 30% to 40% of CD4-deficient mice. CONCLUSIONS: CD4(+) T cells preferentially mediate HSK, but, in their absence, a high infectious dose of HSV-1 can induce histologically similar but transient HSK that is mediated by CD8(+) T cells.     

复发性单疱病毒性角膜炎实验模型的研究

目的：建立一种可靠、实用的复发性单疱病毒性角膜炎（HSK）的实验模型。方法：用单纯病毒I型（HSV－1）Mckrae株行NIH鼠的角膜接种,用人的抗HSV－1血清行鼠的腹腔内注射,使病毒在三叉神经节或角膜内建立起潜伏感染。用紫外线B光照射鼠的角膜,诱导HSK复发。观察诱导HSK复发的成功率、复发性HSK的临床特征、组织学特点。结果：紫外线照射诱导鼠HSK复发的成功率为72．5％,复发性HSK主要表现为基质型角膜炎,组织切片见角膜基质层内有大量的淋巴细胞和一些中性粒细胞浸润。     

Detection of herpes simplex virus type 1, 2 and varicella zoster virus DNA in recipient corneal buttons

AIM: To study the value of polymerase chain reaction (PCR) analysis, to detect viral DNA in recipient corneal buttons taken at the time of penetrating keratoplasty (PKP) in patients with an initial diagnosis of herpetic stromal keratitis (HSK). Since HSK has a tendency to recur, an accurate diagnosis of previous HSK could be the reason to start antiviral treatment immediately, thereby possibly decreasing the number of graft failures due to recurrent herpetic keratitis. METHODS: Recipient corneal buttons and aqueous humour (AH) samples were obtained at the time of PKP from HSK patients (n=31) and from other patients (n=78). Eye bank corneas were also used (n=23). Herpes simplex virus type 1 (HSV-1), type 2 (HSV-2), and varicella zoster virus (VZV) infection were assessed by PCR and antibody detection. RESULTS: The clinical diagnosis HSK could be confirmed by PCR for HSV-1 in 10/31 (32%). In these corneal buttons HSV-2 DNA was detected in 1/31 (3%) and VZV DNA in 6/31 (19%). Intraocular anti-HSV antibody production was detected in 9/28 AH samples tested (32%). In the other patient derived corneas HSV-1 DNA was detected in 13/78 (17%), including eight failed corneal grafts without clinically obvious herpetic keratitis in the medical history. In clear eye bank corneas HSV-1 was detected in 1/23 (4%). CONCLUSIONS: PCR of HSV-1 on corneal buttons can be a useful diagnostic tool in addition to detection of intraocular anti-HSV antibody production. Furthermore, the results were suggestive for the involvement of corneal HSV infection during allograft failure of corneas without previous clinical characteristic signs of herpetic keratitis.     

Sensory Nerve Retraction and Sympathetic Nerve Innervation Contribute to Immunopathology of Murine Recurrent Herpes Stromal Keratitis

PurposeHerpes stromal keratitis (HSK) represents a spectrum of pathologies which is caused by herpes simplex virus type 1 (HSV-1) infection and is considered a leading cause of infectious blindness. HSV-1 infects corneal sensory nerves and establishes latency in the trigeminal ganglion (TG). Recently, retraction of sensory nerves and replacement with “unsensing” sympathetic nerves was identified as a critical contributor of HSK in a mouse model where corneal pathology is caused by primary infection. This resulted in the loss of blink reflex, corneal desiccation, and exacerbation of inflammation leading to corneal opacity. Despite this, it was unclear whether inflammation associated with viral reactivation was sufficient to initiate this cascade of events.MethodsWe examined viral reactivation and corneal pathology in a mouse model with recurrent HSK by infecting the cornea with HSV-1 (McKrae) and transferring (intravenous [IV]) human sera to establish primary infection without discernible disease and then exposed the cornea to UV-B light to induce viral reactivation.ResultsUV-B light induced viral reactivation from latency in 100% of mice as measured by HSV-1 antigen deposition in the cornea. Further, unlike conventional HSK models, viral reactivation resulted in focal retraction of sensory nerves and corneal opacity. Dependent on CD4⁺ T cells, inflammation foci were innervated by sympathetic nerves.ConclusionsCollectively, our data reveal that sectoral corneal sensory nerve retraction and replacement of sympathetic nerves were involved in the progressive pathology that is dependent on CD4⁺ T cells after viral reactivation from HSV-1 latency in the UV-B induced recurrent HSK mouse model.     

Apoptosis in human non-necrotizing stromal herpes simplex keratitis

BACKGROUND: Herpes simplex virus (HSV-1) stromal keratitis is an immune-mediated disease. Recently, it has been shown that infection of cells with HSV-1 induces apoptosis. In this study we investigated the presence of apoptotic cell death in keratectomy specimens from patients with HSV-1 stromal keratitis. PATIENTS AND METHODS: Keratectomy specimens from six patients with HSV-1 non-necrotizing stromal keratitis were chosen and compared to healthy corneas. Paraffin sections were analyzed histologically and cryosections were studied by the immunoperoxidase technique for the presence of HSV-1, Fas and FasLigand (FasL) antigens. Apoptosis was assessed by TUNEL assay (TdT-mediated dUTP nick-end labeling). RESULTS: In healthy corneas, Fas was detected in the epithelium, keratocytes and endothelium; FasL was present in the epithelium and endothelium; TUNEL-positive cells were only found in the superficial epithelial cells. In contrast, inflammatory cells and scars were found in all HSV-diseased corneas; HSV-1 antigen was detected in only one specimen. Cells within inflammatory infiltrations and epithelium were apoptotic. Fas was detected in all corneal cell layers and inflammatory cells. FasL was restricted to areas of inflammation. CONCLUSIONS: The data suggest that apoptosis plays a role in the pathogenesis of HSV keratitis. The Fas-FasL system appears to be involved in the induction of apoptosis. Apoptosis could be involved in the depletion of inflammatory cells in the cornea and may limit the extension of viral replication to the eye.