Expression of vascular endothelial growth factor and its receptors in inflamed and vascularized human corneas

PURPOSE: To help further define the possible role of vascular endothelial growth factor (VEGF) in the pathogenesis of corneal neovascularization, the expression of VEGF and of its receptors Flt-1 and Flk-1 was investigated in various inflammatory corneal diseases. METHODS: Polyclonal antibodies to VEGF and its receptors were used for immunohistochemical staining of frozen sections of 38 human corneas with various degrees of neovascularization and inflammation. In addition, a panel of monoclonal antibodies was used to characterize the composition of the inflammatory infiltrates and to confirm the presence of neovascularization. Furthermore, VEGF concentrations were determined in vascularized corneas using a sensitive enzyme-linked immunosorbent assay. RESULTS: VEGF was expressed by epithelial cells, by corneal endothelial cells, by vascular endothelial cells of limbal vessels and of newly formed vessels in the stroma, and weakly by keratocytes. Furthermore, VEGF expression was often markedly increased in inflamed corneas on epithelial cells and on vascular endothelial cells, particularly in the vicinity of macrophage infiltrates, and on fibroblasts in scar tissue. Correspondingly, VEGF concentrations were significantly higher in vascularized corneas compared with normal control corneas (P < 0.001). Expression of both VEGF receptors, Flt-1 and Flk-1, was increased on endothelial cells of newly formed vessels in the stroma of inflamed corneas compared with limbal vessels of normal control corneas. In addition, Flt-1 was also expressed by corneal endothelial cells and by macrophages, whereas Flk-1 expression was lacking. CONCLUSIONS: These results demonstrate that VEGF, Flt-1, and Flk-1 are strongly expressed in inflamed and vascularized human corneas and, thus, may play an important role in corneal neovascularization.     

Lymphatic vessels in vascularized human corneas: immunohistochemical investigation using LYVE-1 and podoplanin

PURPOSE: To determine whether lymphatic vessels exist in vascularized human corneas, by using immunohistochemistry with novel markers for lymphatic endothelium. METHODS: Human corneas exhibiting neovascularization secondary to keratitis, transplant rejection, trauma, and limbal insufficiency (n = 21) were assessed for lymphatic vessel content by conventional transmission electron microscopy and by immunostaining and immunoelectron microscopy with antibodies specific for the lymphatic endothelial markers, lymphatic vessel endothelial hyaluronan receptor (LYVE-1) and the 38-kDa integral membrane glycoprotein podoplanin. In addition, corneas were stained for the lymphangiogenic growth factor VEGF-C, and its receptor VEGFR3 by immunohistochemistry and in situ RNA hybridization, respectively. RESULTS: Thin-walled, erythrocyte-free vessels staining with lymphatic markers (LYVE-1 and podoplanin) were found to constitute 8% of all vessels, to be more common in the early course of neovascularization, to be always associated with blood vessels and stromal inflammatory cells, and to correlate significantly with the degree of corneal hemangiogenesis (r = 0.6; P = 0.005). VEGF-C, VEGFR3, podoplanin, and LYVE-1 colocalized on the endothelial lining of lymphatic vessels. With immunogold labeling, LYVE-1 and podoplanin antigen were found on endothelial cells lining vessels with ultrastructural features of lymph vessels. CONCLUSIONS: Immunohistochemistry with novel lymph-endothelium markers and ultrastructural analyses indicate the existence of lymphatic vessels in vascularized human corneas. Human corneal lymphangiogenesis appears to be correlated with the degree of corneal hemangiogenesis and may at least partially be mediated by VEGF-C and its receptor VEGFR3.     

促红细胞生成素(Epo)及其受体(EpoR)在正常及碱烧伤诱导的鼠新生血管化角膜上的表达(英文)

目的:促红细胞生成素(Epo)是促红细胞生成的因子,由胎儿肝脏和成人肾脏产生,是贫血及缺氧时的一种应答反应。视网膜异常血管形成,如早产儿视网膜病变(ROP),增殖性糖尿病性视网膜病变(PDR)时Epo水平增高,提示Epo在病理性眼部血管生成中的作用。Epo参与视网膜血管生成,但其与角膜新生血管是否有关尚未见报道。本研究旨在探讨Epo/EpoR是否在正常和新生血管化角膜表达及角膜内注射Epo是否可诱发角膜新生血管的产生,从而了解其与角膜新生血管的联系。方法:(1)制备碱烧伤诱导鼠角膜新生血管模型,免疫组织化学的方法检测Epo及EpoR是否在正常角膜及新生血管化角膜表达;(2) Epo的克隆、表达及纯化;(3)角膜基质内分别注射Epo(6μL,1μg)及Epo对照(载体对照)及盐水,第14d观察角膜是否有新生血管产生。结果:Epo及EpoR在正常角膜及碱诱发的新生血管化角膜的角膜上皮细胞,角膜内皮细胞,基质细胞均有表达,并在新生血管化角膜表达加强,同时也在基质内炎症细胞及新生血管均有表达。角膜基质内注射Epo后第14d,6眼中5眼产生新生血管,对照组6眼均未见新生血管。结论:本文首次报道了Epo及其受体表达于正常角膜和新生血管化角膜。角膜内注射注射Epo可诱发角膜新生血管。Epo及其受体系统与角膜新生血管化的形成有关。     

Expression of tissue inhibitor of metalloproteinase-4 in normal human corneal cells and experimental corneal neovascularization

PURPOSE: To study the expression of TIMP-4 in cultured corneal cells and in corneal neovascularization. METHODS: Human limbo-corneal epithelial cells, fibroblasts, and endothelial cells were cultured in serum-free, PMA- or basic fibroblast growth factor (bFGF)-treated condition. Neovascularization in rat cornea was induced by suturing. The expression of TIMP-4 was examined by immunohistochemistry, Western blot and RT-PCR. RESULTS: TIMP-4 was constitutively expressed in cultured human corneal cells. The expression was only mildly enhanced after mitogen treatment. TIMP-4 immunoreactivity was predominantly expressed in normal rat corneal epithelium, and also in ingrowing blood vessels following suturing, which persisted up to day 28. Increased staining in corneal epithelium and blood vessels were also noted in vascularized human corneas. CONCLUSIONS: TIMP-4 is expressed in the cornea, which may play a role in modulating extracellular matrix remodeling associated with corneal wound healing and angiogenesis.     

Endothelin modulation of choroidal blood flow in the rabbit

Based on the previous finding that locally produced nitric oxide (NO) and endothelin (ET) exert competing effects on choroidal resistance vessels, the present study sought to further characterize the pharmacology of ET in the choroid. The specific goal was to quantify the choroidal blood flow responses to acute changes in perfusion pressure before and after administering endothelin 1 (ET1), a non-selective ET antagonist, and selective antagonists for the endothelin A (ETA) and endothelin B (ETB) receptor subtypes. Anesthetized rabbits were instrumented with an ear artery cannula to measure mean arterial pressure (MAP), occluders on the aorta and vena cava to control MAP, and a vitreous cannula to measure intraocular pressure (IOP). Choroidal blood flow was measured by laser Doppler flowmetry with a vitreous fiber optic probe. The protocol entailed changing the ocular perfusion pressure by varying MAP before and after ET1 (0.9 microg kg(-1), i.v., n = 14), non-selective ET blockade (A-182086, 3 mg kg(-1), i.v., n = 10), selective ETA blockade (FR-139317, 3 mg kg(-1), i.v., n = 12), and selective ETB blockade (A-192621, 3 mg kg(-1), i.v., n = 14). ET1 and ETB blockade shifted the choroidal pressure-flow relation downward, while the non-selective antagonist and the selective ETA antagonist had no effect. The choroid had a biphasic response to exogenous ET1 as seen in other tissues (i.e. initial brief dilation followed by prolonged constriction) that was blocked by the non-selective antagonist whereas the ETA antagonist enhanced the dilation and blocked the constriction, and the ETB antagonist blocked the dilation and enhanced the constriction. These results indicate that ETA and ETB receptors are present and mediate opposing effects on choroidal vascular resistance. The results also suggest that endogenous ET preferentially elicits ETB vasodilation, most likely by stimulating endothelial nitric oxide release.     

Comparison of EphA receptor tyrosine kinases and ephrinA ligand expression to EphB-ephrinB in vascularized corneas

PURPOSE: Eph cell surface receptors and their ligands, ephrins, are involved in neuronal patterning and neovascularization. Our purpose is to compare and characterize the expression of ephrinA ligands and EphA receptors to ephrinB ligands and EphB receptors in excised mouse corneal tissue, in corneal epithelial and keratocyte cell lines, and during corneal angiogenesis. METHODS: Mouse corneal epithelial cells and keratocytes were immortalized using SV40T antigen viral infection of primary cultures. The immortalized epithelial cells and keratocytes were cloned and characterized using antibodies to keratin, vimentin, integrin alpha5beta1, and alpha-smooth muscle actin. Basic fibroblast growth factor pellets were implanted to induce corneal neovascularization. The eyes of wild-type, ephrinB2(tlacZ/+), and EphB4(tlacZ/+) heterozygous mice were harvested and sectioned 7 days after pellet implantation. Confocal immunohistochemistry was performed to compare the expression of the Eph/ephrinA family (EphA1-8, ephrinA1-5) and Eph/ephrinB family (EphB1-4, EphB6 ephrinB1-3). RESULTS: EphA1, EphA3, ephrinA1, ephrinA2, EphB1, EphB4, ephrinB1, and ephrinB2 were detected in wild-type mouse corneal epithelial cells and keratocytes. EphA2 was immunolocalized only in epithelial cells. Also, EphA3, ephrinA1, EphB1, EphB4, and ephrinB1 were immunolocalized to the corneal epithelium and stroma. In the vascularized corneas, ephrinB1 was immunolocalized mainly to the keratocytes around the vessels, and ephrinB2, EphB1, and EphB4 were colocalized mainly with CD31 to the vascular endothelial cells. CONCLUSIONS: The characterization of ephrin ligand and Eph receptor expression during cornea angiogensis in this study suggests that the Eph/ephrin family of receptor tyrosine kinases and their ligands may play a role in the regulation of corneal angiogenesis.     

Expression of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) in inflammation-associated corneal neovascularization

Matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) are all implicated in the development of neovascularization. To investigate the possible role of these factors in corneal neovascularization we have analysed the expression of MMP-2, MMP-9 and VEGF in a rat model of inflammation-associated corneal neovascularization. In this model, corneal neovascularization was induced in Long-Evans rats by krypton laser photocoagulation whereafter eyes were enucleated at 1, 4, 7, 10 and 20 days. Slit-lamp biomicroscopy and histologic analysis revealed a gradual development of corneal neovascularization that peaked 7-10 days after treatment when newly formed vessels could be seen throughout the corneal surface reaching deep into the stroma. Antisense and sense riboprobes were generated using DNA complementary to MMP-2, MMP-9 and VEGF, and mRNA expression was analysed using in situ hybridization. The expression of MMP-2 and MMP-9 in untreated corneas was low or absent whereas VEGF was weakly expressed in the corneal epithelium. MMP-2 expression was increased during corneal neovascularization and was mainly localized to the cells infiltrating areas of new vessel formation. Many of these cells appeared to be inflammatory cells. VEGF expression had a similar overall distribution to MMP-2 during neovascularization with the exception that its expression in the corneal epithelium remained and even increased slightly. MMP-9 was prominently expressed at the border of regenerating corneal epithelium in areas with epithelial wounding but was not detected in the vascularized stroma. Together, the results of the present study support a role for MMP-2 and VEGF in inflammation-associated corneal neovascularization whereas MMP-9 instead appears to be involved in corneal epithelial wound-healing.     

角膜移植后角膜新生淋巴管与新生血管间的关联

目的:研究角膜移植后角膜新生淋巴管与新生血管间关联。方法:人角膜取自行二次角膜移植的19名患者。5核苷酸酶-碱性磷酸酶(5-nase-Alkaline phosphatase,5-NA-ALP)双重酶组织化学染色及淋巴内皮细胞受体(lymphatic vessel endothelial receptor,LYVE-1)、内皮细胞黏附因子-1(platelet endothelial cell adhesion modecule-1,PECAM-1)双重免疫组化法标记角膜中的新生血管和淋巴管,并进行淋巴管计数(lymphatic vessels counting,LVC)和血管计数(blood vessels counting,BVC),比较BVC与LVC之间的关联。结果:角膜中存在角膜新生血管12例(63%),存在角膜新生淋巴管5例(26%)。角膜新生淋巴管仅出现在血管化角膜中。角膜移植后BVC与LVC间呈显著性正相关(r=0.725;P<0.01)。结论:人角膜移植后角膜新生淋巴管与新生血管之间存在密切关联。     

血管内皮生长因子及其受体在病变角膜的表达和临床意义的探讨

目的：探讨血管内皮生长因子（vacular endothelial growth factor,VEGF)及其受体flt-l在各种病变角膜的表达和可能的作用。方法：收集正常周边角膜和角膜缘组织11例和各种病变的角膜标本32例。冰冻切片,用免疫组织化学方法检查标本内VEGF及其flt-1,分析其VEGF的表达与临床表现的关系。结果：VEGF在血管化和非血管化角膜标本均为阳性,在角膜上皮和病变基质表达较强;flt-l在大多数标本呈现阳性反应。在基质和内皮病变角膜VEGF表达高于正常角膜的表达（P＜0．05）,在浸润炎症细胞和增殖组织中的表达与角膜混浊程度、新生血管面积呈正相关（P＜0．05）。结论：各种病变角膜均表达了VEGF及其受体,VEGF在角膜损伤的修复和新生血管化可能起着重要作用。     

血管内皮钙黏蛋白对实验性角膜新生血管的作用及机制

目的 探讨血管内皮钙黏蛋白（VE-cadherin）在实验性角膜新生血管发生过程中的作用及机制。方法 动物实验研究。以碱烧伤诱导构建小鼠角膜新生血管模型;RT-PCR法检测VE-cadherin在碱烧伤角膜组织中的表达;碱烧伤1周后角膜局部应用阻断性抗小鼠VE-cadherin抗体进行干预,碱烧伤3周后大体观察角膜新生血管的发生情况以及全角膜铺片CD31荧光组织化学法检测角膜组织新生血管的面积;RT-PCR检测烧伤角膜组织内caspase-3 mRNA的表达;流式细胞术检测角膜组织血管内皮细胞凋亡数目;体外实验进一步验证VE-cadherin对血管内皮细胞（HREC）血管网形成的影响。采用成组t检验方法处理数据。结果 碱烧伤3周后,VE-cadherin抗体干预组角膜新生血管数目较对照组明显减少。RT-PCR结果显示VE-cadherin抗体干预组caspase-3基因水平表达增高;进一步流式细胞术检测结果显示VE-cadherin抗体干预后,角膜组织内凋亡的血管内皮细胞明显增多。体外实验证实VE-cadherin抗体明显抑制HREC细胞系血管网的形成。结论 VE-cadherin钙黏蛋白能通过维护细胞间黏附以及抑制细胞的凋亡等作用保护实验性角膜新生血管内皮细胞的生长,从而维持新生血管的发生发展。     

内皮素-1对体外培养人小梁网细胞纤维连接蛋白及Ⅰ型胶原表达的影响

目的观察内皮素-1（ET-1）对人小梁网细胞（TMCs）细胞外基质纤维连接蛋白（FN）、Ⅰ型胶原（COL Ⅰ）的影响。方法取死亡24h内尸眼小梁网组织,行TMCs原代和传代培养,并用FN、层黏连蛋白（LN）、神经元特异性烯醇化酶（NSE）和Ⅷ因子相关抗原（FⅧRAg）鉴定为人TMCs后,取传3代的人TMCs,给予不同浓度ET-1（10^-9、10^-8、10^-7mol／L）孵育72h后,免疫荧光和Western blot观察ET-1对TMCs中FN、COLⅠ表达的影响;然后取传3代的人TMCs,分别给予10^-7mol／L ET-1、10^-7mol／L ET-1＋10^-7mol／L ETA受体拈抗剂、10^-mol／L ET-1＋10^7mol／L ETB受体拈抗剂后孵育72h,Western blot观察ET受体拮抗剂对FN、COL Ⅰ表达的影响。结果研究受到伦理委员会的批准,取材前征得供体家属的知情同意。培养的细胞形态多样,含少许色素颗粒,FN、LN、NSE染色均呈阳性反应,FⅧRAg呈阴性反应。人TMCs与10^-9～10^-7mol／L ET-1共孵育后FN表达上调（F=18．41,P〈0．05）;与10^-8mol／L、10^-7mol／L ET-1共孵育后COLⅠ表达上调（F=39．81,P〈0．05）,并呈浓度依赖性,10^-7mol／L时作用最明显;给予ETA受体拮抗剂后,与ET-1组相比,FN、COLⅠ的表达均降低（qFN=7．213,P〈0．05;qCOLⅠ=6．187,P〈0．05）,但给予ETB受体拮抗剂后,FN、COLⅠ的表达均无明显变化。结论ET-1能够促进体外培养的人TMCs中FN、COLⅠ的表达,其机制可能是通过激动ETA受体而非ETB受体发挥作用的。     

Corneal lymphangiogenesis correlates closely with hemangiogenesis after keratoplasty

AIM: To examine the relationship between corneal lymphangiogenesis and hemangiogenesis after keratoplasty. · METHODS: Nineteen human corneas were obtained from 19 patients undergoing a second corneal transplantation in Zhongshan Ophthalmic Center in 2005. Blood and lymphatic vessels in human transplanted corneas were identified by lymphatic vessel endothelial receptor (LYVE-1) and platelet endothelial cell adhesion modecule-1 (PECAM-1) immunohi- stochemistry, and double enzyme-histochemistry; then the association of corneal blood vessel counting (BVC) with lymphatic vessel counting (LVC) was examined. · RESULTS: Corneal hemangiogenesis was present in 12 cases (63%), and lymphangiogenesis occurred in 5 cases (26%) human transplanted corneas. In addition, corneal lymphangiogenesis was only present in vascularized corneas. LVC was strongly and positively correlated with BVC(r=0.725, P <0.01). · CONCLUSION: Corneal lymphangiogenesis develops after keratoplasty and strongly associates with hemangiogenesis.     

Activation of ocular surface mast cells promotes corneal neovascularization

PurposeMast cells, historically known for their effector function in the induction of allergic diseases, reside in all vascularized tissues of the body in particular proximity to blood and lymphatic vessels. As neighboring sentinel cells to blood vessels, mast cells have been associated with angiogenesis. Here we assess the direct contribution of mast cells to neovascularization at the ocular surface.MethodsCorneal neovascularization was induced by placing a single figure-of-eight intrastromal suture 1 mm from the limbus in mast cell-deficient (cKit^W-sh), C57BL/6, and Balb/c mice. Corneas were harvested at 6 h post-suture to quantify cKit⁺FcεR1⁺ mast cells using flow cytometry and tear wash was collected within 6 h to measure β-hexosaminidase and tryptase. Neovascularization was assessed using slit-lamp biomicroscope and immunohistochemistry analysis of corneas harvested on day 4 post-suture. To investigate the effects of mast cells on blood vessel growth, mast cells were co-cultured with vascular endothelial cells (VECs), and tube formation and proliferation of VECs were measured. 2% cromolyn was administered locally to inhibit mast cell activation in vivo.ResultsPlacement of corneal suture activates ocular surface mast cells, which infiltrate into the cornea adjacent to new vessels. Mast cell-deficient mice develop significantly fewer new vessels following suture placement. Mast cells directly promote VEC proliferation and tube formation, partly through secreting high levels of VEGF-A. Pharmacological inhibition of mast cell activation results in significantly less corneal neovascularization.ConclusionOur data demonstrate that ocular surface mast cells are critical to corneal neovascularization, suggesting mast cells as a potential therapeutic target in the treatment of corneal neovascularization.     

Unique homologous siRNA blocks hypoxia-induced VEGF upregulation in human corneal cells and inhibits and regresses murine corneal neovascularization

PURPOSE: To determine whether RNA interference (RNAi) could block hypoxia-induced upregulation of vascular endothelial growth factor (VEGF) in human corneal epithelial cells in vitro and inhibit and regress injury-induced murine corneal neovascularization in vivo. METHODS: siRNA selected on the basis of target sequence homology between mouse and human VEGF was placed into expression cassettes and transfected into human corneal epithelial cells. Hypoxia-induced VEGF synthesis was assayed. Also, the effect of a plasmid capable of directing the expression of an siRNA against VEGF when injected into mouse corneas 8 hours before alkali-mechanical trauma was studied. Leukocyte count, VEGF protein levels, and degree of neovascularization in corneas were compared with that of a control siRNA plasmid. Plasmids were injected 1 week after injury to assess the ability of RNAi to regress corneal neovascularization. RESULTS: Hypoxia-induced VEGF mRNA synthesis and protein secretion by human corneal epithelial cells was efficiently suppressed by an siRNA targeted against a sequence uniquely identical for the mouse and human VEGF genes. Intrastromal delivery of a plasmid expressing this siRNA before murine corneal injury suppressed corneal VEGF by 55.7% versus control (P = 0.014), leukocyte infiltration by 69.5% (P < 0.001), and neovascularization 1 week after injury by 72.3% (P = 0.001). At the regression time point, treated corneas had 72.8% less neovascularization (P < 0.001). CONCLUSIONS: RNAi significantly suppresses expression of VEGF induced by hypoxia in human corneal epithelial cells in vitro. In vivo, intrastromal delivery of a plasmid expressing siRNA against VEGF suppresses injury-induced VEGF expression, leukocyte infiltration, and angiogenesis and was able to regress corneal neovascularization.     

角膜新生淋巴管与血管内皮生长因子C

角膜新生淋巴管（CL）存在于血管化角膜上，常引起并加重角膜混浊和角膜移植排斥反应，是重要的致盲原因之一。血管内皮生长因子C（VEGF—C）是血管内皮生长因子（VEGF）家族成员之一，是VEGFR-2和VEGFR-3受体的配体。VEGF-C通过与VEGFR-3结合促进淋巴管增生，是一个特异性的淋巴管生长因子，在CL形成中起着重要的作用。就近年来CL研究进展及与VEGF—C的关系进行综述。     

Endothelin-3 regulation of retinal hemodynamics in nondiabetic and diabetic rats

PURPOSE: To investigate the mechanisms of action of endothelin (ET)-3 on the regulation of retinal hemodynamics in diabetic and nondiabetic rats. METHODS: Retinal blood flow changes were measured using video fluorescein angiography. Measurements were made before and after intravitreal injections of different ET-3 concentrations in nondiabetic rats and rats with streptozotocin (STZ)-induced diabetes. The effect of ET-3 on retinal blood flow was also investigated in nondiabetic rats after pretreatment with N:(G)-monomethyl-L-arginine (L-NMMA), a nitric oxide synthase (NOS) inhibitor; BQ-788, an ET receptor B (ETB) antagonist; and BQ-123, an ET receptor A (ETA) antagonist. Control animals were injected intravitreally with vehicle alone. RESULTS: In nondiabetic rats, ET-3 induced a dose-dependent rapid increase in retinal blood flow 2 minutes after intravitreal injection (maximal at 10(-)(8) M, P < 0. 01) followed 15 and 30 minutes after ET-3 injection by dose-dependent decreases in retinal blood flow (maximal effect at 10(-)(6) M, P < 0.05). The ET-3-stimulated retinal blood flow increase was inhibited by 10(-)(4) M BQ-788 (P < 0.01) and 10(-)(3) M L-NMMA (P < 0.05). The ET-3-stimulated decrease in retinal blood flow at later times (15 minutes) was inhibited (P < 0.03) by 10(-4) M BQ-123. In diabetic rats, baseline retinal blood flows were decreased compared with nondiabetic rats (P < 0.01), showed dose-dependent increases 2 minutes after ET-3 injection (P < 0.03), and at later times remained significantly increased (P < 0.05) in contrast to flows in nondiabetic rats. CONCLUSIONS: The ET-3-induced initial rapid retinal blood flow increase in nondiabetic rats is mediated by the ET-3/ETB and NOS action. The subsequent retinal blood flow decrease is mediated by ET-3/ETA action. Diabetic rats showed comparable ET-3-induced retinal blood flow increases indicating normal ET-3/ETB action. However, at later times, retinal blood flow remained increased, suggesting an abnormal ET-3/ETA action.     

Corneal lymphangiogenesis: evidence,mechanisms, and implications for corneal transplant immunology

PURPOSE: The normal cornea is devoid of blood and lymphatic vessels but can become vascularized secondary to a variety of corneal diseases and surgical manipulations. Whereas corneal (hem)angiogenesis, i.e., the outgrowth of new blood vessels from preexisting limbal vessels, is obvious both clinically and histologically, proof of associated corneal lymphangiogenesis has long been hampered by invisibility and lack of specific markers. This has changed with the recent discovery of the lymphatic endothelial markers vascular endothelial growth factor receptor 3, LYVE-1 (a lymphatic endothelium-specific hyaluronan receptor), Prox 1, and Podoplanin. METHODS: We herein summarize the current evidence for lymphangiogenesis in the cornea and describe its molecular markers and mediators. Furthermore, the pathophysiologic implications of corneal lymphangiogenesis for corneal transplant immunology are discussed. RESULTS: Whereas corneal angiogenesis in vascularized high-risk beds provides a route of entry for immune effector cells to the graft, lymphangiogenesis enables the exit of antigen-presenting cells and antigenic material from the graft to regional lymph nodes, thus inducing alloimmunization and subsequent graft rejection. CONCLUSIONS: Antilymphangiogenic strategies may improve transplant survival both in the high- and low-risk setting of corneal transplantation.     

Muc4 expression during blood vessel formation in damaged rat cornea

PURPOSE: To determine the timing of Muc4 expression during the association of endothelial cells to form blood vessels in the rat corneal stroma after corneal wounding. METHODS: Corneal damage was inflicted using brief cauterization with silver nitrite. Contralateral and wounded corneas were examined at time periods after wounding by immunohistochemistry and immunofluorescence for Muc4 and for the blood vessel endothelial cell marker von Willebrand Factor. RESULTS: Blood vessels and von Willebrand Factor-stained cells were very sparse in corneal stroma from unwounded corneas. In contrast, aggregates of von Willebrand Factor-stained cells were prevalent in wounded corneas at days 4-5 and 7-10. Muc4 expression was limited at days 4-5, but extensive at days 7-10. CONCLUSION: Muc4 expression develops in endothelial cells during the mid-stages of cell aggregation and blood vessel formation.