Latanoprost does not affect immune privilege of corneal allografts

The present study determined whether topical latanoprost, a prostaglandin (PG) F(2alpha) analog, influences the induction of anterior chamber-associated immune deviation (ACAID), corneal neovascularization (NV) or survival of corneal allografts in mice. BALB/c mice received topical latanoprost or PGE(2) once or multiple times daily starting 4 weeks prior to or the day of anterior chamber injection of C57BL/6 splenocytes. Induction of allo-specific ACAID was assessed by ear challenge with C57BL/6 splenocytes 1 week after subcutaneous immunization. In a separate experiment, orthotopic corneal transplantation was performed using C57BL/6 mice as donors and BALB/c mice as recipients. Recipients were randomized in a masked fashion to receive topical latanoprost or PGE(2). Graft fate was assessed clinically under surgical microscopy. Presence of MHC class II(+) CD11c(+) or CD11b(+) cells in normal BALB/c mouse eyes following latanoprost or PGE(2) administration was assessed immunohistochemically. Control mice received topical 20% dimethyl sulfoxide or no treatment. Allo-specific ACAID was induced after 2 or 6 weeks of once daily treatment with latanoprost, and was induced even after 6 weeks of multiple treatments with latanoprost. Conversely, mice receiving PGE(2) failed to develop ACAID. Opacity and corneal NV scores for allografts treated with latanoprost were statistically indistinguishable from those for control allografts (p>0.05), whereas all allografts treated with PGE(2) were rejected. Opacity and NV scores were significantly higher in these allografts than in controls (p<0.05). A number of MHC class II(+) CD11c(+) cells were present in the central cornea after PGE(2) treatment. Topical application of latanoprost does not influence induction of ACAID or graft outcomes including opacity and NV, whereas PGE(2) does. Immune privilege of corneal allograft is maintained after topical latanoprost application in mice.     

Lymphoma allografts abrogate immune privilege within the anterior chamber of the eye

Immune privilege is extended to allogeneic tissues placed into the anterior chamber of the eye and results in part from the induction of anterior chamber-associated immune deviation (ACAID)--a condition in which the host is capable of making humoral antibodies and cytotoxic T cells specific for the antigens in question, but is selectively suppressed in its capacity to generate delayed-type hypersensitivity (DTH). Privilege is extended only transiently to tissue differing at the major histocompatibility complex; by contrast, privilege is complete for tissues offering multiple minor H incompatibilities, but no MHC disparity. During examination of host responses to tumor cell lines in this latter category, it was observed that privilege was extended to all histologic categories of tumors examined except T cell lymphomas. Moreover, the capacity of minor H incompatible tumors to maintain immune privilege and sustain prolonged survival within the anterior chamber could be abrogated if T cell lymphomas were placed into the anterior chamber of the contralateral eye. Thus, T cell lymphomas exert a systemic influence which robs the anterior chamber of its immune privilege. It is concluded that this systemic effect is intimately related to lymphokines produced by T cell lymphoma allografts. Since immune privilege seems to be a physiologic property of the anterior chamber, it is suspected that local features within this site conspire to insure that antigens placed therein interact with the immune system in a manner that bypasses lymphokine production, thus allowing for the induction of ACAID and selective suppression of DTH.     

免疫赦免在小鼠角膜移植排斥中的作用研究

目的:阐明同种异体小鼠角膜移植术后免疫排斥反应及免疫赦免的相关性。方法:建立小鼠原位角膜移植及同种异体小鼠角膜移植实验模型。观察原位移植与同种异体移植术后角膜植片发生排斥的情况,对比两种移植术后植片的存活率,了解小鼠角膜移植术后发生排斥反应与免疫赦免反应之间的关系。结果:小鼠原位角膜移植术后植片100%存活;同种异体小鼠角膜移植术后存活率为25%。结论:小鼠角膜移植术后免疫排斥并非绝对,免疫赦免在角膜移植术中发挥重要作用。     

T cell subsets in the immune rejection of murine heterotopic corneal allografts

Using a previously described murine heterotopic corneal allograft model, we examined the roles of delayed-type hypersensitivity (DTH) and cytotoxic T lymphocytes (CTL) in corneal allograft rejection. We have previously shown that normal C57BL/6 mice consistently reject heterotopic corneal allografts within 14 days of grafting. These hosts develop antigen-specific CTL responses but no evidence of DTH reactivity. The absence of DTH suggested that this T cell subset was unnecessary for corneal allograft rejection. The present studies using T cell-deficient mice selectively reconstituted with specific T cell subsets confirmed this suspicion. T cell-deficient (i.e., adult thymectomized, lethally irradiated, bone marrow-reconstituted = ATXBM) C57BL/6 mice were selectively reconstituted with the following categories of syngeneic lymph node cells (LNC): BALB/c skin-immune LNC treated with anti-Lyt 1 antibody + complement; BALB/c skin- or cornea-immune LNC treated with anti-Lyt 2 antibody + complement; or BALB/c cornea- or skin-immune LNC not treated with antibody. ATXBM mice reconstituted with syngeneic Lyt 1-depleted, BALB/c skin-immunized LNC failed to develop DTH, yet rapidly rejected BALB/c corneal allografts. Similarly, ATXBM mice reconstituted with Lyt 1-depleted cornea-immune LNC did not demonstrate DTH responses but were able to reject 100% of the corneal allografts in an accelerated fashion. By contrast, corneal allograft rejection was significantly delayed in ATXBM mice reconstituted with cornea-immune LNC partially depleted of Lyt 2+ T cells. Collectively, the results indicate that: heterotopic corneal allografts can be rejected in the absence of DTH; heterotopic corneal allografts fail to induce allospecific DTH; and partial depletion of Lyt 2+ CTL leads to a prolongation of heterotopic corneal allograft survival. Thus, the primary T cell-dependent immune effector elements responsible for heterotopic corneal allograft rejection appears to reside in the cytolytic T lymphocyte population.     

Ocular immune privilege in the year 2010: ocular immune privilege and uveitis

The phrase "immune privilege" was coined by Peter Medawar to describe the absence of an immune response to allografts placed into the anterior chamber of the eye or brain. We now understand that immune privilege is more than a passive microenvironment with a distinctive anatomical structure that holds back immunity. The ocular microenvironment actively engages the immune system with immunosuppressive biochemical mechanisms. The unique characteristics of ocular immune privilege appear designed to protect the eye from damage while preserving foveal vision, thus providing the host with a definite survival advantage. However, the protection is not always sufficient and the eye becomes susceptible to uveitis. Uveitis is an intraocular inflammatory disorder that encompasses a wide range of underlying etiologies. It may be idiopathic or associated with systemic disease or infection. Understanding the biochemistry of immune privilege has the potential to identify its weaknesses that allow for immunity to break through.     

前房相关免疫偏离对碱烧伤眼角膜移植的影响

目的观察诱导供体特异性的前房相关免疫偏离(ACAID)是否有助于角膜植片在碱烧伤高危眼中的存活。方法用1mol/L的NaOH烧灼新西兰白兔单眼角膜中央建立高危眼模型,然后将动物随机分为诱导组和对照组,1个月后进行角膜移植。诱导组在角膜移植前10d前房植入供体肌肉诱导供体特异性ACAID,对照组未处理。观察诱导组与对照组相比角膜植片存活时间是否延长。结果与对照组相比,诱导ACAID组角膜植片平均存活时间延长,两组植片存活率的差异具有显著统计学意义。结论诱导供体特异性ACAID有助于碱烧伤高危眼角膜植片的存活。     

Rejection of corneal allografts

Corneal graft rejection is the major cause of penetrating keratoplasty failure. It is a complex immunological process that involves recognition of alloantigens from the corneal graft by the host's immune system, leading to an efferent immune response against the graft. Each layer of the cornea can undergo rejection, endothelial rejection being the most severe form. In some cases, rejection will lead to corneal graft failure. Many donor- and host-related risk factors contribute to corneal graft rejection. Corticosteroid therapy, topical or systemic, is the gold-standard in the preventive and curative treatment of rejection. Other immunosuppressive agents are promising but require further evaluation. Early detection of rejection is essential to establish an aggressive treatment and reduce the risk of graft failure. Prevention of rejection is also based on tissue matching between donor and recipient. In high-risk patients, ABO compatibility decreases the risk of rejection. HLA compatibility could positively influence corneal graft survival in some cases.     

Ocular immune privilege in the immunosuppressive intraocular microenvironment

Immune privilege exists in the normal eye (anterior chamber, vitreous cavity, subretinal space): when foreign tissue/cellular grafts are placed in the eye, rejection is largely, if not completely, avoided. The ineffectiveness of the immune response in this circumstance results from eye-dependent alterations in (a) the induction of systemic immunity to graft antigens, and (b) the expression of cell-mediated immunity within the eye. Recent evidence indicates that eye-derived factors, present in the intraocular microenvironment, modify the afferent and efferent limbs of the immune response. Studies of aqueous humor as a prototype of the intraocular microenvironment have demonstrated that this fluid profoundly inhibits antigen-driven T cell activation such that proliferation and lymphokine production are curtailed. Moreover, aqueous humor modifies the functional properties of conventional antigen presenting cells (APC) such that exogenous antigens are processed uniquely. When antigen-pulsed APC exposed to aqueous humor are injected intravenously, they induce Anterior Chamber Associated Immune Deviation (ACAID). Several factors in aqueous humor have been implicated as immunosuppressants: transforming growth factorbeta, alpha-melanocyte stimulating hormone, vasoactive intestinal peptide, calcitonin gene related peptide, and hydrocortisone (because Cortisol binding globulin is virtually absent). In certain experimentally-induced ocular disorders, resident ocular cells fail to secrete immunosuppressive factors constitutively, and this may explain why immune privilege is also lost.     

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.     

细菌性眼内炎的免疫赦免及免疫应答机制

细菌性眼内炎是能导致视力严重受损的眼科重症,即使采取了及时和积极的药物及手术干预,仍会造成眼部组织不可逆的损伤.对细菌性眼内炎的研究热点是研究眼部组织对感染的免疫反应及病原微生物和宿主组织间分子和细胞的相互作用.目前国内外对细菌性眼内炎免疫应答机制的研究包括免疫赦免、固有免疫反应、补体系统、Fas配体、炎性细胞浸润、细胞因子及细胞间黏附因子的作用等方面.     

Leukocyte adhesion molecules in rejected corneal allografts

Leukocyte adhesion molecules are believed to play a key role in the selective recruitment of different leukocyte populations to inflammatory sites. In this study, we investigated the presence and distribution of intercellular ad hesion molecule-1 (ICAM-1), E-selectin (endothelial leukocyte adhesion molecule-1) and vascular cell adhesion molecule-1 (VCAM1) in 12 rejected corneal allografts and compared the presence of these adhesion molecules with the composition of the associated inflammatory infiltrates. ICAM-1 was focally expressed on corneal epithelial cells and its expression was increased on keratocytes, corneal and vascular endothelial cells particulary at the site of dense infiltration with mononuclear leukocytes. E-selectin was present on endothelial cells of vessels in the stroma of rejected corneal allografts which were characterized by dense infiltration with T cells and macrophages. VCAM-1 was predominantly expressed on inflammatory cells of the macrophage/monocyte lineage, but only sporadically on vascular endothelial cells in thet stroma of vascularized rejected corneal allografts. Our results suggest that ICAM-1, E-selectin and VCAM-1 may all be involved in the pathogenesis of corneal allograft rejection, particulary in the generation of the inflammatory infiltrates.     

眼免疫赦免的细胞和分子基础

眼的免疫赦免是一极其复杂和动态的免疫调节过程。这一机制是眼生物进化过程的一种生理适应,对于维持视觉器官的完整性、免受免疫性炎症反应的破坏,以及为眼组织移植提供适宜的微环境起着重要的作用。就眼免疫赦免和前房相关免疫偏离（ＡＣＡＩＤ）中的眼局部因素、维持眼免疫赦免的细胞和分子基础等问题进行了讨论。     

Ocular inflammation with varicella-zoster virus and immune privilege

Mice with experimental acute retinal necrosis (ARN) induced by herpes simplex virus fail to acquire virus-specific delayed hypersensitivity (DH), even though they produce antiviral antibodies. We investigated whether there was a similar correlation for patients with varicella zoster virus(VZV)-induced ARN or patients with anterior uveitis caused by VZV. Patients with acute, VZV-induced ARN, with anterior uveitis with dermatitis(herpes zoster ophthalmicus, ZO-AU), or with anterior uveitis without dermatitis(zoster sine herpete, ZSH-AU) were skin-tested with VZV to evaluate DH. All patients with VZV-induced skin disease alone(control group) displayed intense DH when tested with VZV antigen. In contrast, subsets of patients with ARN or ZO-AU displayed absent VZV-specific DH. Patients with the most severe ARN or ZO-AU had the lowest DH responses to VZV antigens. Serum anti-VZV antibody titers were higher in ARN patients than in normal subjects, and anti-viral titer correlated inversely with intensity of anti-VZV DH responses. VZV-specific DH responses were restored in patients who recovered from ARN or from anterior uveitis caused by VZV. Patients with ZSH-AU also failed to display VZV-specific DH. Absence of DH reactivity to VZV antigens appears to be a concomitant feature of VZV-uveitis of high intensity.     

同种异体大鼠角膜移植物TRAIL及其受体DR4的表达与免疫排斥反应的关系

目的观察大鼠角膜移植术后角膜组织中肿瘤坏死因子相关凋亡诱导配体（TNF-related apoptosis-inducing ligand，TRAIL）及其死亡受体4（death receptor4，DR4）的表达情况，分析其与角膜移植免疫排斥反应的关系。方法实验对象分为移植组和对照组，移植组采用大鼠同种异体穿透性角膜移植模型，术后每日观察排斥反应指数的变化，分别于术后不同时间点（7d、10d、14d）取角膜植片，采用免疫组织化学法（SABC法）检测TRAIL及DR4蛋白表达情况，并与对照组正常大鼠角膜组织TRAIL及DR4蛋白表达情况相比较。结果TRAIL及DR4主要表达于正常角膜上皮层，在基质层及内皮层有极少量表达；而移植组急性排斥期角膜植片各层TRAIL及DR4表达均增高，阳性表达主要集中在植片伤口附近的上皮层及浅层基质。结论与正常角膜相比，同种异体角膜移植术后急性排斥期植片各层TRAIL及DR4蛋白表达均增高，由此推测TRAIL及其受体DR4与角膜移植急性免疫排斥反应的发生发展有关。     

Thrombospondin plays a vital role in the immune privilege of the eye

PURPOSE: The role of thrombospondin (TSP)-1 in TGF-beta activation and T-cell suppression was studied in the retinal pigment epithelial (RPE) cells, a monolayer of pigmented cells that line the subretinal space, an immune-privileged site in the eye. METHODS: Posterior eyecups were prepared by excising the anterior segment, lens, and retina from enucleated eyes of C57BL/6, thrombospondin-1 knockout (TSP-1KO), and TGF-beta2 receptor II double-negative (TGF-beta2 RII DN) mice, leaving behind a healthy monolayer of RPE resting on choroid and sclera. Serum-free medium was added to these RPE eyecups, and, after various time intervals, supernatants (SNs) were removed and tested. RESULTS: SNs of an ex vivo culture of RPE cells from C57BL/6 mice were shown to inhibit both antigen and anti-CD3 activation of T cells, partially due to constitutive production of TGF-beta and to the ability of RPE to activate the latent form of TGF-beta. Activation of TGF-beta was entirely dependent on TSP-1, also produced by RPE. SNs of RPE from TSP-1KO mice failed to inhibit T-cell activation. Ovalbumin (OVA)-specific delayed hypersensitivity (DH) was not impaired when OVA was injected either into the subretinal space or into the anterior chamber of TSP-1KO mice before OVA immunization. Moreover, experimental autoimmune uveoretinitis was significantly more intense in eyes of TSP-1KO mice and failed to undergo spontaneous resolution unlike wild-type mice. CONCLUSIONS: Production of both TSP-1 and active TGF-beta by RPE is essential to the creation and maintenance of immune privilege in the subretinal space and that the immune privilege limits the severity and duration of retinal inflammation due to autoimmunity.