基质金属蛋白酶2、9和血管内皮生长因子在碱烧伤小鼠角膜组织中的表达

采取滤纸片放置法,用1mol／L的NaOH在小鼠角膜中央进行碱烧伤,建立动物模型。取烧伤前和烧伤后的小鼠角膜制备组织切片,用抗MMP2、抗MMP9和抗VEGF的抗体分别进行免疫组化染色,检测它们在碱烧伤前后的小鼠角膜组织中的蛋白表达情况;提取碱烧伤前和碱烧伤后不同时间点的小鼠角膜组织的总RNA并进行逆转录,以获得的逆转录产物作为模板,用特异的引物和探针进行实时定量PCR,分别检测MMP2、MMP9和VEGF在碱烧伤前后的小鼠角膜组织中转录水平的变化;提取碱烧伤前后小鼠角膜的蛋白组分,用明胶底物酶谱的方法检测其中MMP2和MMP9的活性变化。结果表明,浸透1mol／L的NaOH的滤纸小片,对小鼠角膜进行碱烧伤可以有效地诱导角膜新生血管形成,烧伤后3-4d就有明显的新生血管形成,至第8、9d左右开始退行。免疫组化结果显示,正常角膜中没有MMP9和VEGF表达,MMP2表达极低;碱烧伤后3种因子的表达均上升。实时定量PCR的结果显示MMP2在碱烧伤后表达升高,第3d达到最高随后下降;MMP9在正常角膜组织中没有表达,碱烧伤后第1d达到最高之后开始下降;VEGF在正常角膜中也没有表达,碱烧伤后第4d达到高峰之后开始下降。以上结果说明碱烧伤后的角膜组织中MMP2、MMP9和VEGF的表达均经历先上升后下降的变化,与角膜愈合及新生血管发育和退化过程相吻合。     

Cells that emerge from embryonic explants produce fibers of type IV collagen

Double immunofluorescence staining experiments designed to examine the synthesis and deposition of collagen types I and IV in cultured explants of embryonic mouse lung revealed the presence of connective tissue-like fibers that were immunoreactive with anti-type IV collagen antibodies. This observation is contrary to the widely accepted belief that type IV collagen is found only in sheet-like arrangements beneath epithelia or as a sheath-like layer enveloping bundles of nerve or muscle cells. The extracellular matrix produced by cells that migrate from embryonic mouse lung rudiments in vitro was examined by double indirect immunofluorescence microscopy. Affinity-purified monospecific polyclonal antibodies were used to examine cells after growth on glass or native collagen substrata. The data show that embryonic mesenchymal cells can produce organized fibers of type IV collagen that are not contained within a basement membrane, and that embryonic epithelial cells deposit fibers and strands of type IV collagen beneath their basal surface when grown on glass; however, when grown on a rat tail collagen substratum the epithelial cells produce a fine meshwork. To our knowledge this work represents the first report that type IV collagen can be organized by cells into a fibrous extracellular matrix that is not a basement membrane.     

Hemidesmosome formation by embryonic chick corneal epithelium in vitro

This study was undertaken in order to determine whether 15-day embryonic chick corneal epithelial cells can form hemidesmosomes when cultured on a variety of substrata. It was found that hemidesmosomes were formed on gelatin films, hydrated collagen gels, lens capsule, scraped corneal stroma, matrix produced by corneal endothelial cells and untreated tissue culture plastic. Hemidesmosomes were found after 5 days in cultures produced from either dissociated epithelial cells or whole epithelial explants. Hemidesmosomes occurred both singly and in groups and their morphology varied between well-defined structures with attachment plaques, sub-basal dense plates and connections to intracellular filamentous networks, and more rudimentary forms. The presence of extracellular material was often associated with the hemidesmosomes, although it was also possible to find hemidesmosomes where this material was absent. This work suggests that, in the embryonic chick cornea, extracellular structures such as anchoring filaments and anchoring fibres often associated with mature hemidesmosomes are not essential for hemidesmosome formation.     

Particular structure of the anterior third of the human true vocal cord.

The histological aspects of the true vocal cord mucosa change in the anterior third compared with the posterior two thirds. The anterior third is characterized by an epithelium where the ridges, marked in the posterior two thirds, are very slight or even absent. The underlying basement membrane, which is thin in the posterior two thirds, here appears particularly thick. At the ultrastructural level in this area, beneath a normally thickened basal lamina, a thick layer of finely granulated electron-dense material, interspersed with thin and randomly scattered collagen fibrils and proteoglycan filaments, is detectable. Beneath this thickened basement membrane, a layer of small undulated collagen fibril bundles with very numerous interspersed oxytalan fibres is found. The collagen fibrils, small in diameter (30-40 nm), seem to continue with the collagen fibrils of the basement membrane. In this layer numerous blood vessels with a very thick, delaminated basement membrane are also observed. The underlying area is characterized by the vocal cord ligament, composed by large compact collagen fibril bundles with interspersed elastic fibres. The particular features of the thick basement membrane, the thick-walled and delaminated vessels and the modular distribution of the elastic system together may well form the basic structure enabling the functional integration of the vocal ligament into the overlying mucosa and the underlying vocal muscle.     

Differential roles for two gelatinolytic enzymes of the matrix metalloproteinase family in the remodelling cornea.

We have documented changes in collagenolytic/gelatinolytic enzymes of the matrix metalloproteinase family (MMP) in remodelling rabbit cornea. MMP-2 (65 kDa gelatinase) in the proenzyme form is synthesized by the cells of the normal corneal stroma. After keratectomy the level of MMP-2 is increased in the stroma and enzyme appears in both pro- and activated forms. In addition, corneal cells synthesize MMP-9 (92 kDa gelatinase) in the proenzyme form after keratectomy; expression occurs in both the epithelial as well as stromal corneal layers. Changes in expression of both enzymes are precisely localized to the repairing portion of cornea, but demonstrate important differences in timing that correlate with the timing of specific events of matrix remodelling. Our data suggest that each of the gelatinases plays a different role in tissue remodelling after injury. We hypothesize that MMP-2 performs a surveillance function in normal cornea, catalyzing degradation of collagen molecules that occasionally become damaged. After wounding, this enzyme appears to participate in the prolonged process of collagen remodelling in the corneal stroma that eventually results in functional regeneration of the tissue. MMP-9 expression does not correlate with stromal remodelling, but we suggest that the enzyme might play a part in controlling resynthesis of the epithelial basement membrane.     

Reconstitution of human epidermis in vitro is accompanied by transient activation of basal keratinocyte spreading

Frozen human cadaver skin obtained from the skin bank was thawed and incubated in serum-free medium for 1–2 days, after which the original epidermis could be removed mechanically. Transmission electron microscopic observations showed that the dermal matrix remaining behind contained intact bundles of collagen fibrils but no live cells and that a continuous lamina densa persisted in the basement membrane region. Indirect immunofluorescence analyses demonstrated linear staining of the basement membrane region by antibodies against laminin and type IV collagen and discontinuous staining with antibodies against fibronectin. Scanning electron microscopic observations revealed a normal topographical arrangement of dermal matrix papilla and interspersed crypts on the surface of the matrix. Epidermal cells placed on the dermal matrix attached in 1–2 h and spread by 24 h. After 1 week of culture the epidermis was reconstituted, at which time approximately 30% of the epidermal cells were basal keratinocytes and the remainder were more differentiated keratinocytes. A high degree of differentiation of the reconstituted epidermis was shown by the formation of hemidesmosomes along the basement membrane, the formation of desmosomes characterized by intercellular dense lines, and the presence of a cell layer containing keratohyalin granules. At various times during epidermal reconstitution, cells were harvested and tested in short-term assays for adhesion to fibronectin substrata. During the first several days there was a transient activation of basal keratinocyte spreading analogous to the modulation of keratinocyte spreading that we have observed during epidermal reconstitution in vivo.     

兔机械性角膜上皮损伤后伤口愈合的形态学动态变化

目的观察兔机械性角膜上皮损伤后伤口愈合的形态学动态变化。方法选取新西兰大白兔12只,随机分为A、B两组,均建立机械性角膜上皮损伤模型（刮除直径为8mm的角膜中央上皮）,术后给予盐酸林可霉素滴眼液滴眼,3次/日,1滴/次。A组在建模后第0、1、4、7天共4个时间点采用前节裂隙灯照相系统进行眼表照相,并计算损伤面积。B组在建模后第1、4、7天,按随机数字表法取2只兔的实验眼角膜,行透射电镜及病理检查。结果前节裂隙灯照相系统记录了不同观察时间点损伤范围（伤口愈合面积）的动态变化。造模后第1天,角膜上皮全层缺如,损伤边缘处上皮细胞胞膜向损伤区内伸出褶皱的伪足;造模后第4天,上皮自周边向缺损区域爬行生长,覆盖整个角膜,可见2～3层细胞,主要为基底细胞和多角细胞,细胞连接松驰;造模后第7天,再生上皮分化较完全,约5～6层细胞,极向齐,连接较紧密,可见均匀分布的半桥粒结构。结论兔机械性角膜上皮损伤后伤口愈合的动态形态学变化包括上皮细胞向心性移行、增殖,以及随后的分化,连接。     

Immunohistochemical study of basement membrane reconstruction by an epidermis-dermis recombination experiment using cultured chick embryonic skin: induction of tenascin.

The production of extracellular matrix components such as laminin, Type IV collagen, fibronectin, and tenascin during the formation of basement membrane in cultured epidermis-dermis recombinant skin of 13-day-old chick embryo was analyzed immunohistochemically. The epidermis and dermis were separated from each other by treatment with EDTA and/or dispase. The basal lamina of the basement membrane was thus removed from both epidermis and dermis. The isolated epidermis was overlaid onto the isolated dermis, i.e., recombined, and then cultured for 1-7 days in a chemically defined medium (BGJb) on a Millipore filter. Immunofluorescence labeling was used for light microscopy and HRP or colloidal gold labeling for electron microscopy. In specimens from 2-day cultures, positive sites of anti-laminin and anti-fibronectin reaction were observed light microscopically as patches which, at the electron microscopic level, corresponded to fragments of the basal lamina located immediately beneath and in the vicinity of the attachment plaques of the hemidesmosomes. The staining pattern became continuous 7 days after recombination. Fluorescence labeling of laminin and fibronectin appeared somewhat earlier than that of Type IV collagen and tenascin. All of the four components were found localized primarily in the basal lamina. Furthermore, fibronectin and tenascin were also distributed in the extracellular matrix of the dermis. The expression of tenascin, which does not exist in the basement membrane of 13-day-old intact embryonic skin, was induced in vitro. These results suggest that hemidesmosomes may play an important role in the reconstruction of the basement membrane and that various components of the basement membrane appeared at different times during the reconstruction.     

Evolution of metaplastic squamous cells of alveolar walls in pulmonary fibrosis produced by paraquat

Sequential histologic, ultrastructural, immunohistochemical and morphometric studies were made of the evolutional changes of metaplastic and regenerating alveolar epithelial cells in monkeys from 3 days to 8 weeks after paraquat administration. In the early proliferative phase, many alveoli were lined by single-layered and stratified squamous epithelium and bronchiolized epithelium (i.e., presumably derived from bronchi and bronchioles). The regenerating epithelial cells had well developed bundles of actin-like filaments, which were arranged parallel to the basal surfaces of the cells and were associated with zonulae adherentes; these cells also had intermediate filaments and some desmosomes, but lacked basement membranes, hemidesmosomes and anchoring fibrils. They covered either denuded, wavy and disrupted original epithelial basement membranes or areas of developing intraalveolar fibrosis. In zones of squamous epithelial cell metaplasia associated with intraalveolar fibrosis, fibronexus-like structures appeared to be responsible for the initial adhesion of the cells to the underlying connective tissue. In later phases, single-layered and stratified squamous epithelial cells disappeared, and only bronchiolized epithelial cells, with hemidesmosomes and anchoring fibrils on their basal surfaces, were found in fibrotic alveoli. Although bronchiolized and squamous metaplastic epithelial cells are generally thought to be formed as late events in pulmonary damage, such cells play an important role in early, temporary repair of damaged alveoli.     

Basement membrane component changes in skeletal muscle transplants undergoing regeneration or rejection

The basement membrane of myofibers plays an important role during orderly regeneration of skeletal muscle after injury. In this report, changes in various basement membrane components were analyzed in skeletal muscle grafts undergoing regeneration (autografts) or immune rejection (allografts). The immunofluorescence technique using specific antibodies against laminin, types IV and V collagen, heparan sulfate proteoglycan, fibronectin, in combination with binding of concanavalin A (ConA) was used to monitor basement membranes. In normal muscle, these components were localized in the pericellular region of myofiber corresponding to its basement membrane. After transplantation, the majority of myofibers underwent degeneration as a result of ischemic injury, followed by regeneration from precursor myosatellite cells. Various components of basement membrane zone disappeared from the degenerating myofibers, leaving behind some unidentifiable component that still bound ConA. A new basement membrane appeared around the regenerated myotubes which persisted during maturation of the regenerating muscle. In rejected skeletal muscles, the immunoreactivity of various components persisted even after the disappearance of myotubes and myofiber cytoplasm. In addition, an accumulation of fibronectin was seen throughout the rejected muscle with the onset of immune rejection. These results demonstrate that the major basement membrane components disappear and reappear sequentially during myofiber degeneration and regeneration. Such a turnover is not seen in rejected skeletal muscles. Thus, the myofiber basement membrane is not a static structure as previously thought but one which changes chemically during degeneration and regeneration. This feature of basement membrane may be important in the orderly regeneration of skeletal muscle after injury.     

Keratinocyte-Targeted Expression of Human Laminin γ2 Rescues Skin Blistering and Early Lethality of Laminin γ2 Deficient Mice

Laminin-332 is a heterotrimeric basement membrane component comprised of the α3, ß3, and γ2 laminin chains. Laminin-332 modulates epithelial cell processes, such as adhesion, migration, and differentiation and is prominent in many embryonic and adult tissues. In skin, laminin-332 is secreted by keratinocytes and is a key component of hemidesmosomes connecting the keratinocytes to the underlying dermis. In mice, lack of expression of any of the three Laminin-332 chains result in impaired anchorage and detachment of the epidermis, similar to that seen in human junctional epidermolysis bullosa, and death occurs within a few days after birth. To bypass the early lethality of laminin-332 deficiency caused by the knockout of the mouse laminin γ2 chain, we expressed a dox-controllable human laminin γ2 transgene under a keratinocyte-specific promoter on the laminin γ2 (Lamc2) knockout background. These mice appear similar to their wild-type littermates, do not develop skin blisters, are fertile, and survive >1.5 years. Immunofluorescence analyses of the skin showed that human laminin γ2 colocalized with mouse laminin α3 and ß3 in the basement membrane zone underlying the epidermis. Furthermore, the presence of “humanized” laminin-332 in the epidermal basement membrane zone rescued the alterations in the deposition of hemidesmosomal components, such as plectin, collagen type XVII/BP180, and integrin α6 and ß4 chains, seen in conventional Lamc2 knockout mice, leading to restored formation of hemidesmosomes. These mice will be a valuable tool for studies of organs deficient in laminin-332 and the role of laminin-332 in skin, including wound healing.     

Hemidesmosomes and anchoring fibril collagen appear synchronously during development and wound healing

Bullous pemphigoid antisera and monoclonal antibodies to type VII collagen were used to localize hemidesmosomes and anchoring fibrils, respectively, in tissues of developing eyes and healing corneal wounds of New Zealand white rabbits. In the 17-day fetal rabbit eye, both antibodies colocalize to the epithelial-stromal junction of the lid and conjunctival region, but neither binds to the cornea, and electron microscopy demonstrates hemidesmosomes only where the antibodies bind. By 20 days of fetal development, the antibodies colocalize in cornea, and, by electron microscopy, hemidesmosomes are shown to be present as well. In healing 7-mm corneal wounds, both antibodies colocalize at the wound periphery within 66 h. By electron microscopy, hemidesmosomes along small segments of basal lamina are also shown to be present at the wound periphery at this time. These demonstrations of the synchronous assembly of hemidesmosomes and anchoring fibrils support the hypothesis of linkage of hemidesmosomes through the basement membrane to anchoring fibrils.     

In vitro and post-transplantation differentiation of human keratinocytes grown on the human type IV collagen film of a bilayered dermal substitute

Using human type IV and type I + III collagens and a new, nontoxic cross-linking procedure, we have developed a cell-free bilayered human dermal substitute for organotypic culture and transplantation of human skin keratinocytes. We have studied the formation of the basement membrane, and the differentiation of keratinocytes grown on the type IV collagen layer of this dermal substitute, in vitro and after grafting onto nude mice. These studies demonstrated the formation of essential constituents of the basement membrane in culture: hemidesmosomes and deposition of extracellular matrix on the top of the type IV collagen were observed as early as 6 days after plating of human keratinocytes. Although the keratinocytes formed a well-organized multilayered epithelium, they exhibited limited differentiation when grown submerged in liquid medium. However, the multilayered sheet obtained after 14 days in submerged culture was composed of a regular basal cell layer, several nucleated suprabasal cell layers containing granular cells, and several dense, anucleated cell layers. The grafting experiments have shown a good biocompatibility of the dermal substitute. It is repopulated by fibroblasts, newly synthesized collagen, vessels, and a few mononuclear cells. At Day 14 after grafting, the type IV collagen layer was still present and very dense, and the basement membrane appeared as in culture, with numerous well-structured hemidesmosomes and deposition of extracellular matrix resembling lamina densa. At Day 55 after transplantation, even if the epidermal graft did not exhibit all the characteristics of the normal epidermis in vivo, it was very close to it. At this stage, the basement membrane was complete, with structures clearly indicative of anchoring fibrils. This new dermal substitute offers many advantages. It is stable and easy to handle. Its production is standardized. The oxidation induced by periodic acid led to a nontoxic cross-linked matrix. This dermal substitute is the first one entirely composed of human collagens. The type I + III collagen underlayer is reorganized when grafted. It supports a type IV collagen top layer which offers an excellent substrate for keratinocytes, favors their anchorage, and favors the formation of the basement membrane in vitro. This dermal substitute could be useful for wound coverage or as an in vitro model for toxicological and pharmacological studies.     

Absence of type IV collagen in the centre of the corneal epithelial basement membrane

Summary Type IV collagen is the basic structural component of all basement membranes (BM), and forms the backbone to which other BM components attach. We have found that in the centre of the adult human cornea the epithelium does not display a type IV collagen immunoreactive BM. In fetal corneas (14 and 22 weeks of gestation), however, the epithelial BM shows uninterrupted type IV collagen immunoreactivity. In similar experiments laminin immunoreactivity was observed in the entire corneal epithelial BM, in fetal as well as adult corneas. Ultrastructurally, a normal BM with a lamina lucida and a lamina densa can be observed in the conjunctiva. The adult corneal centre, however, shows epithelium without a lamina densa. Focal deposits of electron-dense material are observed in conjunction with hemidesmosomes and anchoring fibres.These observations indicate that in the development of the eye, the cornea is initially covered with an epithelium which attaches to a normal BM. Later on, however, the BM type IV collagen disappears from the corneal centre. Assuming that highly differentiated epithelium cannot produce a BM, this could be due to the high level of differentiation of central corneal epithelium, which is generated in the limbal proliferation zone. Alternatively, the acellular Bowman's layer might lack triggers to induce type IV collagen production by the epithelial cells.     

Laminin chains in the basement membranes of human thymus

Summary In recent studies, the α2 chain of laminin (Ln) has been suggested to be the only laminin α chain expressed in mouse and human thymus. We have now used chain-specific monoclonal antibodies and indirect immunofluorescence microscopy to study the expression of laminin chains in samples of foetal and 6-year-old human thymus. The subepithelial basement membrane of the capsule of foetal 16- to 18-week thymus presented a bright immunoreactivity for Ln α1, α3, β1, β3 and γ1 chains but not for α2 chain, suggesting the expression of laminins-1 and-5. Most cortical and medullary epithelial cells, including Hassall's corpuscles, however, lacked laminin immunoreactivity. Immunoreactivity for Ln β2 chain was only seen in basal laminae of larger blood vessels. In thymic specimens from 6-year-old children, immunoreactivity for the laminin α1, α3, β1, β3 and γ1 chains was invariably found in subepithelial basement membrane of the capsule and that for laminin α2 chain was now also distinct but more heterogeneous. Furthermore, the thymic subepithelial basement membrane of the capsule at all stages showed immunore-activity for collagen type VII, forming the anchoring fibres in epithelial basement membranes. The subcapsular thymic epithelium also showed immunoreactivity for the BP 230 antigen and β₄ integrin subunit, both components of hemidesmosomes. The present results show that the thymic subepithelial basement membrane of the capsule presents properties which are commonly seen in stratified and combined epithelia, and are compatible with suggestions of the antigenic similarity of thymic epithelial cells and keratinocytes.     

AN ELECTRON MICROSCOPE STUDY OF THE EPITHELIUM IN THE NORMAL MATURE AND IMMATURE MOUSE CORNEA

1. An electron microscope study at high resolution of the corneal epithelium of the normal mature and immature mouse revealed new information regarding the submicroscopic appearance of these cells. 2. Two thin dense lines separated by a less dense area constituted the structure of the limiting surface membrane of epithelial cells; the thickness of this membrane was about 80 A. 3. Some differences in the appearance of the cytoplasm and mitochondria of cells from the immature mouse cornea and the appearance of the cytoplasm and mitochondria of cells from the adult mouse cornea were observed. 4. The basement membrane appeared as a dense band about 600 A wide separating the basal epithelial cells from the substantia propria. Suggestions of periodicity were seen in some phosphotungstic acid-treated specimens. 5. Round bodies believed to be bacteria were seen on the surface of the outer epithelial cells in the adult mouse cornea but not in the immature, unopened eye.     

Staining of proteoglycans in mouse lung alveoli. II. Characterization of the Cuprolinic Blue-positive, anionic sites

Summary The nature of Cuprolinic Blue-positive anionic filaments in mouse lung alveoli has been characterized. The contrast of filaments in the alveolar basement membrane of type I epithelial cells was lost on treatment with nitrous acid and pronase (without prefixation). In contrast, neither neuraminidase, chondroitinase ABC or AC, norStreptomyces hyaluronidase had any effect. Treatment with pronase (after prefixation) and 2.0m MgCl₂ (after prefixation) also had no effect, indicating that the filaments are heparan sulphate proteoglycans. The filaments in the alveolar basement membrane of type II epithelial cells and in the capillary basement membrane of the endothelial cells were also nitrous acid sensitive, but chondroitinase ABC-insensitive. A model in which the whole alveolus contains a single layer of heparan sulphate-containing proteoglycan monomers is proposed. Furthermore, the collagen fibril associated filaments remained unaffected after treatment with nitrous acid, neuraminidase orStreptomyces hyaluronidase, or after digestion with pronase (after prefixation) and treatment with 2.0m MgCl₂ (after prefixation). These filaments, however, could no longer be detected when digestion with chondroitinase ABC or pronase (without prefixation) was applied; chondroitinase AC treatment clearly affected the filaments, although they still were visible. These results indicate that the filaments are dermatan sulphate-containing proteoglycans. Some functional aspects of the proteoglycans are discussed.     

Hemidesmosomes of normal and regenerating mouse corneal epithelium

Hemidesmosomes of normal mouse corneal epithelium observed in tangential thin sections, occupy 14% of the basal plasma membrane. They consist of linear chains of densities with an orientation that is not random with respect to the radial axis of the cornea, tending to parallel it. During the repair of a small epithelial defect, cells of the corneal epithelium peripheral to the defect show chains of hemidesmosomes arranged parallel to the direction of migration of the epithelial sheet. This is parallel to the radius, like the orientation of the normal chains. Cells of the area that was denuded of epithelium, and is being resurfaced, show no hemidesmosomes. During repair of a large defect of the corneal epithelium hemidesmosomes are present on the cells covering the denuded area but they are small, few in number compared to the normal, and many are not arranged in chains. These small hemidesmosomes appear to be points of attachment of very fine basal filaments, possibly actin.     

The Role of Free Radicals in Paraquat-Induced Corneal Lesions

Paraquat is a synthetic bipyridylium salt widely used as herbicide and defoliant. Enzyme-catalyzed redox-cycling of paraquat generates oxygen radicals. The toxic, even lethal, effects of paraquat are due to free radical-mediated tissue injury. Ocular lesions, sometimes quite severe, have been observed following accidental splashing of paraquat solutions onto the eyes.

These studies were designed to document the generation of paraquat free radicals in corneal tissue, and to describe the histological nature of the corneal injuries in experimental animals (rabbits and monkeys). The EPR spectrum of rabbit corneas, 30 min. after intrastromal injection of paraquat, showed the signal of the free radical of paraquat. Ultrastructural studies of corneas 8 days after intrastromal injections (100μl) of paraquat solutions showed that the initial lesions occur at the epithelium/basement membrane interface. In rabbit cornea, dose dependent lesions were observed, i.e. whereas 50 mM paraquat caused only minimal damage to the epithelial basement membrane, 75 mM caused complete dissolution to the basement membrane with some damage to stromal collagen, and loss of epithelium with stromal ulceration and severe inflammatory response were observed with 150 mM paraquat. Monkey corneas were less susceptible than those of rabbits to the effects of paraquat. No lesions were observed following intrastromal injections of 50 mM or 75 mM paraquat. With higher concentrations of paraquat (100 mM and 150 mM) the primary injuries were to the proximal and lateral plasma membranes of basal epithelial cells; basement membrane alterations were detected only adjacent to areas of significant plasma membrane damage. The underlying Bowman's membrane and stroma were not affected. Anatomical differences between the corneas of rabbit and monkeys as well as possible biochemical differences may account for the species differences observed.