Immunohistochemical staining of the human anterior segment. Evidence that resident cells play a role in immunologic responses

Emergent Temporal Signaling in Human Trabecular Meshwork Cells: Role of TRPV4-TRPM4 Interactions

Trabecular meshwork (TM) cells are phagocytic cells that employ mechanotransduction to actively regulate intraocular pressure. Similar to macrophages, they express scavenger receptors and participate in antigen presentation within the immunosuppressive milieu of the anterior eye. Changes in pressure deform and compress the TM, altering their control of aqueous humor outflow but it is not known whether transducer activation shapes temporal signaling. The present study combines electrophysiology, histochemistry and functional imaging with gene silencing and heterologous expression to gain insight into Ca²⁺ signaling downstream from TRPV4 (Transient Receptor Potential Vanilloid 4), a stretch-activated polymodal cation channel. Human TM cells respond to the TRPV4 agonist GSK1016790A with fluctuations in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and an increase in [Na⁺]_i. [Ca²⁺]_i oscillations coincided with monovalent cation current that was suppressed by BAPTA, Ruthenium Red and the TRPM4 (Transient Receptor Potential Melastatin 4) channel inhibitor 9-phenanthrol. TM cells expressed TRPM4 mRNA, protein at the expected 130-150 kDa and showed punctate TRPM4 immunoreactivity at the membrane surface. Genetic silencing of TRPM4 antagonized TRPV4-evoked oscillatory signaling whereas TRPV4 and TRPM4 co-expression in HEK-293 cells reconstituted the oscillations. Membrane potential recordings suggested that TRPM4-dependent oscillations require release of Ca²⁺ from internal stores. 9-phenanthrol did not affect the outflow facility in mouse eyes and eyes from animals lacking TRPM4 had normal intraocular pressure. Collectively, our results show that TRPV4 activity initiates dynamic calcium signaling in TM cells by stimulating TRPM4 channels and intracellular Ca²⁺ release. It is possible that TRPV4-TRPM4 interactions downstream from the tensile and compressive impact of intraocular pressure contribute to homeostatic regulation and pathological remodeling within the conventional outflow pathway.

A Review of Imaging Biomarkers of the Ocular Surface

A biomarker is a "characteristic that is measured as an indicator of normal biological processes, pathogenic processes, or responses to an exposure or intervention, including therapeutic interventions." Recently, calls for biomarkers for ocular surface diseases have increased, and advancements in imaging technologies have aided in allowing imaging biomarkers to serve as a potential solution for this need. This review focuses on the state of imaging biomarkers for ocular surface diseases, specifically non-invasive tear break-up time (NIBUT), tear meniscus measurement and corneal epithelial thickness with anterior segment optical coherence tomography (OCT), meibomian gland morphology with infrared meibography and in vivo confocal microscopy (IVCM), ocular redness with grading scales, and cellular corneal immune cells and nerve assessment by IVCM. Extensive literature review was performed for analytical and clinical validation that currently exists for potential imaging biomarkers. Our summary suggests that the reported analytical and clinical validation state for potential imaging biomarkers is broad, with some having good to excellent intra- and intergrader agreement to date. Examples of these include NIBUT for dry eye disease, ocular redness grading scales, and detection of corneal immune cells by IVCM for grading and monitoring inflammation. Further examples are nerve assessment by IVCM for monitoring severity of diabetes mellitus and neurotrophic keratitis, and corneal epithelial thickness assessment with anterior segment OCT for the diagnosis of early keratoconus. However, additional analytical validation for these biomarkers is required before clinical application as a biomarker.

[The trabecular meshwork: Structure, function and clinical implications. A review of the littérature (French translation of the article)]

Glaucoma is a blinding optic neuropathy, the main risk factor for which is increased intraocular pressure (IOP). The trabecular meshwork, located within the iridocorneal angle, is the main pathway for drainage of aqueous humor (AH) out of the eye, and its dysfunction is responsible for the IOP elevation. The trabecular meshwork is a complex, fenestrated, three-dimensional structure composed of trabecular meshwork cells (TMC) interdigitated into a multilayered organization within the extracellular matrix (ECM). The purpose of this literature review is to provide an overview of current understanding of the trabecular meshwork and its pathophysiology in glaucoma. Thus, we will present the main anatomical and cellular bases for the regulation of aqueous humor outflow resistance, the pathophysiological mechanisms involved in trabecular dysfunction in the various types of glaucoma, as well as current and future therapeutic strategies targeting the trabecular meshwork.

The trabecular meshwork: Structure, function and clinical implications. A review of the literature

Glaucoma is a blinding optic neuropathy, the main risk factor for which is increased intraocular pressure (IOP). The trabecular meshwork, located within the iridocorneal angle, is the main pathway for drainage of aqueous humor (AH) out of the eye, and its dysfunction is responsible for the IOP elevation. The trabecular meshwork is a complex, fenestrated, three-dimensional structure composed of trabecular meshwork cells (TMC) interdigitated into a multilayered organization within the extracellular matrix (ECM). The purpose of this literature review is to provide an overview of current understanding of the trabecular meshwork and its pathophysiology in glaucoma. Thus, we will present the main anatomical and cellular bases for the regulation of aqueous humor outflow resistance, the pathophysiological mechanisms involved in trabecular dysfunction in the various types of glaucoma, as well as current and future therapeutic strategies targeting the trabecular meshwork.

The many faces of the trabecular meshwork cell

With the combined purpose of facilitating useful vision over a lifetime, a number of ocular cells have evolved specialized features not found elsewhere in the body. The trabecular meshwork (TM) cell at the irido-corneal angle, which is a key regulator of intraocular pressure, is no exception. Examination of cells in culture isolated from the human TM has shown that they are unique in many ways, displaying characteristic features of several different cell types. Thus, these neural crest derived cells display expression patterns and behaviors typical of endothelia, fibroblasts, smooth muscle and macrophages, owing to the multiple roles and two distinct environments where they operate to maintain intraocular pressure homeostasis. In most individuals, TM cells function normally over a lifetime in the face of persistent stressors, including phagocytic, oxidative, mechanical and metabolic stress. Study of TM cells isolated from ocular hypertensive eyes has shown a compromised ability to perform their daily duties. This review highlights the many responsibilities of the TM cell and its challenges, progress in our understanding of TM biology over the past 30 years, as well as discusses unanswered questions about TM dysfunction that results in IOP dysregulation and glaucoma.

Human trabecular meshwork cells exhibit several characteristics of, but are distinct from, adipose-derived mesenchymal stem cells

PURPOSE

To support the growing promise of regenerative medicine in glaucoma, we characterized the similarities and differences between human trabecular meshwork (HTM) cells and human mesenchymal stem cells (hMSCs).

METHODS

HTM cells and hMSCs were phenotypically characterized by flow cytometry. Using quantitative polymerase chain reaction, the expression of myoc, angptl7, sox2, pou5f1, and notch1 was determined in both cell types with and without dexamethasone (Dex). Immunosuppressive behavior of HTM cells and hMSCs was determined using T cells activated with phytohemagglutinin. T-cell proliferation was determined using BrdU incorporation and flow cytometry. Multipotency of HTM cells and hMSCs was determined using adipogenic and osteogenic differentiation media as well as aqueous humor (AH). Alpha-smooth muscle actin (αSMA) expression was determined in HTM cells, hMSCs, and HTM tissue.

RESULTS

Phenotypically, HTM and hMSCs expressed CD73, CD90, CD105, and CD146 but not CD31, CD34, and CD45 and similar sox2, pou5f1, and notch1 expression. Both cell types suppressed T-cell proliferation. However, HTM cells, but not hMSCs, upregulated myoc and angptl7 in response to Dex. Additionally, HTM cells did not differentiate into adipocytes or osteocytes. Culture of hMSCs in 20%, but not 100%, AH potently induced alkaline phosphatase activity. HTM cells in culture possessed uniformly strong expression of αSMA, which contrasted with the limited expression in hMSCs and spatially discrete expression in HTM tissue.

CONCLUSIONS

HTM cells possess a number of important similarities with hMSCs but lack multipotency, one of the defining characteristics of stem cells. Further work is needed to explore the molecular mechanisms and functional implications underlying the phenotypic similarities.

A new insight into the cellular regulation of aqueous outflow: how trabecular meshwork endothelial cells drive a mechanism that regulates the permeability of Schlemm's canal endothelial cells

AIM

To test the hypothesis that trabecular meshwork endothelial cells (TMEs) increase the permeability of Schlemm's canal endothelial cells (SCEs) by actively releasing ligands that modulate the barrier properties of SCEs.

METHODS

The TMEs were first irradiated with a laser light and allowed to condition the medium, which is then added to SCEs. The treatment response is determined by both measuring SCE permeability (flow meters) and the differential expression of genes (Affymetrix chips and quantitative polymerase chain reaction (PCR)). The cytokines secreted by the treated cells were identified using ELISA and the ability of these cytokines to increase permeability is tested directly after their addition to SCEs in perfusion experiments.

RESULTS

SCEs exposed to medium conditioned by the light activated TMEs (TME-cm) respond by undergoing a differential expression (DE) of 1,120 genes relative to controls. This response is intense relative to a DE of only 12 genes in lasered SCEs. The TME-cm treatment of SCEs increased the SCE permeability fourfold. The role of cytokines in these responses is supported by two findings: adding specific cytokines established to be secreted by lasered TMEs to SCEs increases permeability; and inactivating the TME-cm by boiling or diluting, abrogates these conditioned media permeability effects.

CONCLUSION

These experiments show that TMEs can regulate SCE permeability and that it is likely that TMEs have a major role in the regulation of aqueous outflow. This novel TME driven cellular mechanism has important implications for the pathogenesis of glaucoma and the mechanism of action of laser trabeculoplasty. Ligands identified as regulating SCE permeability have potential use for glaucoma therapy.

Langerhans cell-like dendritic cells in the cornea, tongue and oesophagus of the chicken (Gallus gallus)

Langerhans cells are dendritic leucocytes which reside mainly within stratified squamous epithelia of skin and mucosa. Their visualization requires the use of ATPase histochemistry, electron microscopy for identifying the unique trilaminar cytoplasmic organelles (the Langerhans cell granules or Birbeck granules), and the expression of major histocompatibility complex class II molecules. Following uptake of antigen, Langerhans cells migrate via the afferent lymphatics to the lymph nodes and undergo differentiation from an antigen-processing cell to an antigen-presenting cell. Using the same approach as that employed in previous studies for the identification of chicken epidermal Langerhans cells, we show here the presence of ATPase-positive and major histocompatibility complex class II-positive Langerhans cell-like dendritic cells at the mucosal surface of the eye, tongue and oesophagus of the chicken. Ultrastructurally, these cells qualified as Langerhans cells except that they lack Langerhans cell granules. Thus, as in mammalian skin and mucosa, chicken mucosa contains mucosal dendritic cells with morphological and phenotypical features for the engagement of incoming antigens within epithelium and lamina propria.

Immunohistochemical studies in equine recurrent uveitis (ERU)

Despite extensive clinical research, the etiology of equine recurrent uveitis (ERU) is still unknown. After an immunologic pathogenesis was established in recurrent uveitis in humans, a similar pathogenic mechanism was assumed to exist in ERU. To investigate whether immunopathologic mechanisms are involved in ERU, 20 eyes of 15 horses with ERU were examined immunohistochemically with a T cell marker, B cell marker, and anti-major histocompatibility complex (MHC) class II antibodies. Twenty-six eyes of 20 horses were used for investigation of MHC class II antigen expression in normal equine eyes. In 18 eyes of 14 horses, the number of T cells in the inflammatory cell population within the uvea was assessed. In 16/18 eyes (89%), the T lymphocyte fraction was > 70%. This cell population was distributed mostly in a diffuse manner throughout the uvea and also within the mantle zone of follicular lymphocytic aggregates. Foci of B lymphocytes could be found within the center of follicular aggregates in three eyes. The expression of MHC class II antigen on resident ocular cells was evaluated in 10 eyes of six horses with ERU. An increase of MHC class II antigen expression in the trabecular meshwork and on the nonpigmented ciliary epithelium was noted as was a deviant expression on proliferating Müller cells and retinal pigment epithelial cells. The predominance of T cells in the inflammatory infiltrates supports the central role of a cell-mediated immune response. Furthermore, the observation of a deviant MHC class II expression on resident ocular cells suggests that aberrant immune regulation may play a role in the pathogenesis of ERU.

The extracellular matrix and its modulation in the trabecular meshwork

The extracellular matrix (ECM) in the trabecular meshwork is is believed to be essential for maintenance of the normal outflow system. Excessive, abnormal accumulations of ECM materials have been noted in the trabecular meshwork of eyes obtained from patients with primary open angle glaucoma. This review summarizes the current knowledge regarding the composition of this matrix and the receptors for ECM proteins in the trabecular meshwork. Modulations of the ECM elements by constituents in the aqueous humor after phagocytic challenges and by glucocorticoids are also described. The ECM is known to regulate cell differentiation and cell behavior in a number of systems. It will thus be of particular interest to establish the relationship between the modulated ECM and the functional status of trabecular meshwork cells and to examine the possible relevance of such modulation to outflow resistance.

The influence of penetrating keratoplasty and cyclosporin A therapy on MHC class II (Ia)-positive cells in the rat iris and choroid

BACKGROUND

The presence of Ia-positive cells (MHC class II equivalent) has been previously reported in the iris and choroid of various species. They have been reported to have both round and dendritic morphologies; the latter may represent classic dendritic cells, potent antigen-presenting cells (APCs). It is possible that the dendritic-like cells play a important role in (auto)immune processes of uveal and other ocular tissues. Using the flat or whole mount technique, the distribution of Ia-positive cells in the rat iris and choroid was investigated following penetrating keratoplasty (PKP) and following treatment with cyclosporin A (CsA).

METHODS

Lewis (LW) rats received corneal buttons from Lewis-Brown Norway (LW-BN) donors and were randomly assigned to the following groups: (i) operated, untreated (n = 24); (ii) operated, CsA-treated (10 mg/kg i.m.; n = 22). Controls were groups (iii) normal LW rats (n = 13); (iv) unoperated, CsA-treated (16 days' treatment; n = 8); (v) anterior perforation of the anterior chamber (n = 3); (vi) eight corneal sutures only (n = 4); (vii) syngeneic operated (LW to LW; n = 4). Animals of groups (i) and (ii) were killed on the 5th, 9th and 13th postoperative days and on appearance of the corneal rejection (group i, day 13; group ii, day 16). Both eyes were enucleated, immediately fixed, and iris-choroid flat mounts were examined for Ia-positive cells using APAAP immunohistochemistry.

RESULTS

In the normal Lewis rat iris, scattered Ia-positive cells of both nondendritic and dendritic morphology were observed. CsA treatment in the unoperated rat did not result in a significant decrease in the percentage of dendritic cells in the iris or choroid. Anterior chamber perforation, the placement of sutures in the cornea and syngeneic PKP resulted in a moderate increase in iris Ia-positive cells. Allogeneic transplantation resulted in a large increase in both types of Ia-positive cells, particularly on day 13 with corneal rejection. In group ii, an initial decrease in Ia-positive cells until day 13 was observed; upon rejection (day 16), the histological picture was similar to that of untreated animals. Alterations in the operated choroid were also apparent following CsA treatment.

CONCLUSION

Corneal transplantation in the Lewis rat results in an increase in Ia-positive cells in the iris; CsA therapy can delay but not prevent this reaction. Changes in choroidal Ia-positive cells following PKP were not apparent, their numbers being affected only by CsA treatment following grafting.

Distinctive distribution of HLA class II presenting and bone marrow derived cells in the anterior segment of human eyes

Cells of bone marrow origin that normally occupy the stroma of the murine iris and ciliary body have been implicated in the immune phenomenon, anterior chamber associated immune deviation (ACAID). Following injection of antigen into the anterior chamber, cells of this type deliver an ACAID inducing signal into the systemic circulation, presumably through the outflow tract. In an effort to identify such cells in man, anterior chambers of 34 human donor eyes of different age groups were stained immunocytochemically with monoclonal antibodies directed at HLA class II molecules, CD 45 (a molecular marker of bone marrow-derived cells) and macrophage-associated membrane molecules (CD 68, CD 14). Within the outflow tissue, the cells of the filtering trabecular meshwork stained with none of those reagents. However, infrequent single, dispersed, dendritic cells were positively stained in the intertrabecular spaces. More numerous labelled cells were found in the anterior- and posterior-most portions of the non-filtering part of the trabecular meshwork. These cells were continuous with stained cells adjacent to the outer wall of Schlemm's canal and to the collector channels. Numerous labelled cells were seen in the vicinity of the intra- and episcleral vessels, the ciliary meshwork, the stroma of the ciliary muscle and epithelial processes, and the iris stroma. With advancing age, increasing numbers of CD 45+, HLA class II expressing cells appeared to accumulate in the so-called uveoscleral pathway. These results indicate that bone marrow-derived cells with the potential to function of ACAID induction reside within human eyes, and that cells of this type are located not only in the stroma of iris and ciliary body, but within the non-filtering portions of the trabecular meshwork and the uveoscleral pathway. The appearance of rare CD 45+ cells "in transit" in the filtering trabecular meshwork is compatible with the view that cells carrying ACAID-inducing signals to the systemic immune apparatus escape from the eye by this route.

Immunohistochemical characterization of dendritic cells and macrophages in the aqueous outflow pathways of the rat eye

Immunohistochemical studies were performed to determine the distribution, phenotype and ontogeny of macrophages and dendritic cells (DCs) in the aqueous humour outflow pathways of the rat eye. Optimal fixation and indirect immunoperoxidase techniques were employed in conjunction with a panel of mAbs on tangential frozen sections of ocular tissues from a total of 37 Wistar Furth rats aged 12-13 days (n = 8), 3 weeks (n = 12), 7 weeks (n = 5) and 15 weeks (n = 12). The density of immunopositive cells was scored qualitatively. A moderate to low density of Ia+ cells with a dendritic morphology were observed in the trabecular meshwork. DCs were also identified in the suprachoroidal space and in the connective tissues of nerves and vessels piercing the sclera, i.e. in association with non-conventional aqueous outflow pathways. The phenotypical and morphological characteristics of these cells would indicate that they may potentially act as antigen presenting cells (APCs). Non-dendritic pleomorphic cells with a macrophage phenotype were also identified in the trabecular meshwork, and bipolar or elongated cells with a macrophage phenotype were a noticeable feature in the perivascular region of collector channels and the limbal episcleral veins. Some macrophage and DC-like cells were observed in intimate association with limbal mast cells. Theories on the mechanisms of Anterior Chamber Associated Immune Deviation (ACAID) have assumed APCs are largely absent from the tissues lining the anterior chamber. Our findings of a low but moderate density of putative APCs in the conventional and non-conventional aqueous humour outflow pathways are discussed in relation to the various theories of ACAID.

Expression of modified low-density lipoprotein receptors by trabecular meshwork cells

We examined the incorporation of fluoresceinated low-density lipoprotein (LDL) and acetylated or acetoacetylated low-density lipoprotein (A-LDL or AA-LDL) by a number of ocular cells in culture. All the cells investigated, including bovine, monkey, human trabecular meshwork cells, human corneal endothelial cells, human corneal stromal cells and human scleral cells, took up fluorescently labeled LDL. The bovine, monkey and human trabecular meshwork cells showed the strongest fluorescence reactions. In addition, we found that the trabecular meshwork cells became fluorescent after incubations with labeled A-LDL or AA-LDL. They were the only cell type examined that possessed this capacity. The fluorescence intensity was markedly diminished by adding to the incubation solution either fucoidin, a competitive inhibitor of modified LDL uptake, unlabeled A-LDL or AA-LDL. The trabecular meshwork cells in situ also became brightly labeled after exposure to fluoresceinated native LDL, A-LDL or AA-LDL. The uptake of modified LDL separated the trabecular meshwork cells from other types of ocular cells, which may be used to aid identification of trabecular meshwork cells in culture as well as in situ. This property also suggested that trabecular meshwork cells may have some functional similarities to macrophages.

Murine trabecular meshwork cells in tissue culture

Trabecular meshwork cells from an inbred strain of mice (A/J) were established in tissue culture. Within 1 hour of enucleation, tissue containing the cornea and the chamber angle was excised and placed in tissue culture. Two to five days later, three cell types grew from the explants. Two of these cell types, corneal endothelium and fibroblasts, grew together, with the fibroblasts preferentially spreading on top of the endothelial cells. The trabecular meshwork cells extended from the explant as a distinct morphological type. The corneal endothelium and its associated fibroblasts were then removed from the culture flask with a sterile cotton swab, leaving a monolayer of pure trabecular meshwork cells. These cells required 3-4 weeks to reach confluency and could be passaged five times. They were actively phagocytic in culture and exhibited immunoreactivity to antibodies against two extracellular matrix components, laminin and collagen type IV. Mouse trabecular meshwork cells also expressed receptors for acetylated low-density lipoprotein, a property shared by trabecular meshwork cells derived from other species. The availability of trabecular meshwork cells from an inbred strain of mice will facilitate future in vivo functional studies of these cells in a syngeneic system, as well as investigations of potential immunoregulatory properties of the trabecular meshwork.

Potential antigen-presenting cells in normal extraocular muscles demonstrated with double immunoenzyme staining

Antigen-presenting cells are of crucial importance for the initiation and regulation of regional immune responses. In a previous study, indirect morphological evidence that morphologically normal human orbital tissues contain HLA-DR-positive macrophages, which may represent antigen-presenting cells, has ben obtained. In the present study, these cells were characterized in detail using double immunoenzyme staining techniques with monoclonal antibodies directed against several well-characterized monocyte/macrophage markers and against HLA-DR gene products. The orbital muscular tissues appear to contain numerous HLA-DR, monocyte/macrophage marker double-stained cells, which are considered to be potential antigen-presenting cells. The cells are widely distributed in the connective tissue of all the orbital muscular tissues studied and consist of several subsets with different phenotypes. Furthermore, site-specific differences were shown between recti muscles and the levator/Müller's muscles with respect to the distribution of HLA-DR and one monocyte/macrophage marker (OKM5). Many of the orbital antigen-presenting cells appear to be of the dendritic type and are considered to be of major importance in regulating local orbital immunity.

Immunopathology of scleritis

Conjunctival and scleral biopsies from 25 patients with necrotizing scleritis and 5 patients with recurrent nonnecrotizing scleritis were studied by histopathologic, immunofluorescence, and immunoperoxidase techniques. Vasculitis with fibrinoid necrosis and neutrophil invasion of the vessel wall was present in 75% of the scleral and 52% of the conjunctival specimens. Vascular immunodeposits were found in 93% of the scleral and 79% of the conjunctival tissue tested by immunofluorescence techniques. A dramatic increase in the number of inflammatory cells over normal controls was detected in both tissues by immunoperoxidase techniques. In the conjunctival epithelium, there were significantly more T-helpers, macrophages, and B cells. In the conjunctival substantia propria, there were significantly more T cells of all types, macrophages, and B cells. Likewise, scleral specimens showed an increase over controls of T cells of all types and macrophages. HLA-DR expression was dramatically increased in both tissues. Immune-complex-mediated vasculitis plays a pivotal role in the pathogenesis of necrotizing scleritis and recurrent nonnecrotizing scleritis. Induced HLA-DR expression on ocular nonimmune cells and T cell controlled responses also may participate.

Electrical and morphological evidence for heterogeneous populations of cultured bovine trabecular meshwork cells

Although trabecular meshwork cells are presumed to play an important role in determining ocular aqueous outflow resistance, little is known about their membrane transport characteristics. As in vivo access by microelectrodes is difficult, we used cell culture techniques to facilitate membrane voltage recording from cultured bovine trabecular meshwork cells. Phase-contrast microscopy revealed the presence of epithelial-like and spindle-shaped cell types. The mean membrane voltage for epithelial cells was -49.7 +/- 0.8 mV (S.E.M., n = 143) and for spindle cells was -70.9 +/- 1.9 mV (S.E.M., n = 48). These cells possess an electrogenic Na+/K(+)-ATPase and a K+ conductance. K transference numbers (tk) for [K+] from 5 to 80 mM were 0.50 for epithelial cells and 0.71 for spindle cells. The epithelial cells lack the electrogenic Na+/HCO3-symport, thereby enabling their differentiation from corneal endothelial cells and confirming previous reports of differences between these cell types. A proportion of spindle cells demonstrated spontaneous and induced fluctuations of membrane voltage. One millimolar Ba2+ (n = 9) induced an immediate depolarization of membrane voltage, with the onset of 'overshooting' action potentials, which were dependent on extracellular Ca2+ and Na+ but were not blocked by tetrodotoxin, 10(-6) M. Spindle cells showed parallel alignment of intracellular smooth muscle specific alpha-isoactin filaments, whereas epithelial cells showed specks of non-fibrous staining. Electron microscopy revealed that epithelial cells had the characteristics of metabolically active cells, with few intermediate filaments (10-12 nm) and microfilaments (6-7 nm) and short cytoplasmic processes. Spindle cells had long cytoplasmic processes and abundant intermediate- and microfilaments. These data provide further evidence for multiple bovine trabecular cell types. The smooth muscle-like spindle cell may represent the previously proposed contractile element of the angle and its action could conceivably alter ocular outflow resistance.

Expression of HLA by the human trabecular meshwork and corneal endothelium

By using immunohistochemical techniques, we demonstrated that HLA class I (A, B and C) and HLA class II (DR), the major histocompatibility antigens in man, are expressed constitutively by cells of the trabecular meshwork/Schlemm's canal system and corneal endothelium, as well as by the conjunctival epithelium, Langerhans cells, vascular endothelium and uvea. Because clinical studies indicate that these antigens are involved in mediating corneal graft rejection and possibly in glaucomatous disease of the eye, the presence of both class I and II HLA in the corneal endothelium and in the trabecular cells has important implications for an understanding of immune disorders in the anterior segment of the eye. The presence of HLA on trabecular cells raises the possibility that these antigens potentiate the recognized role of Langerhans cells at the limbus and that they participate in, and/or regulate, the maintenance and defense of the aqueous outflow pathway. Our findings also open up the possibility of using HLA as a genetic marker in the determination of susceptibility to these disorders in man.

Fibronectin induces migration of bovine trabecular meshwork cells in vitro

The migration of cultured bovine trabecular meshwork cells in response to fibronectin was studied using a 48-well migration chamber. Fibronectin was shown to be a potent chemoattractant for these cells, with a dose optimum of 30 micrograms ml-1. At this dose, the number of migrated cells was approximately 12 times that of the control, which was serum-free medium. Analysis of the migratory response revealed it to be mainly a chemokinesis, but chemotaxis was a substantial component. Electron microscopy demonstrated that adhesion and spreading of cells on the surface of the pore-containing membrane are necessary prerequisites to their migration through a pore. Microspikes are abundant during the movement of cellular processes into and through the pores. The migrated cells are extremely thin with a large surface area, but despite this phenotypic alteration the ultrastructure of migrated cells is unchanged.

Longwave ultraviolet radiation (UVA, 320-400 nm)-induced tan protects human skin against further UVA injury

The protective effect of a UVA (320-400 nm) induced tan against cutaneous injury by further UVA-irradiation was studied by evaluating the histopathologic changes in tanned and untanned normal human buttock skin 24 h after exposure to 2 and 4 minimal erythema doses of UVA. In each subject there were fewer polymorphonuclear leukocytes and less endothelial cell prominence and vessel wall necrosis in the UVA tanned skin than in the untanned UVA-irradiated skin. In the tanned control and tanned UVA-irradiated skin there was a prominent mononuclear cell inflammatory infiltrate that was much greater than in untanned skin. In immunoperoxidase stained tissue sections, the mononuclear cells were predominantly T cells, and in all of the specimens the number of phenotypic helper/inducer cells exceeded the phenotypic cytotoxic/suppressor cells. This demonstrates that a UVA tan provides photoprotection against acute UVA exposure. In addition, tanning, with or without further UVA-irradiation, was associated with a mononuclear cell inflammatory infiltrate.