Mucosa specific lymphocytes in the human conjunctiva, corneoscleral limbus and lacrimal gland

Mucosa-Associated Lymphoid Tissue and Tertiary Lymphoid Structures of the Eye and Ear in Laboratory Animals

Mucosa-associated lymphoid tissue (MALT) of special senses is poorly described and can be confused with nonspecific mononuclear cell infiltrates and tertiary lymphoid structures (TLS). In the eye, MALT consists mostly of conjunctiva-associated lymphoid tissue (CALT) and lacrimal drainage-associated lymphoid tissue (LDALT). In humans, CALT and LDALT are important components of the normal eye-associated lymphoid tissue (EALT), but EALT is less frequently described in ocular tissues of animals. The EALT are acquired postnatally in preferential mucosal sites, expand with antigenic exposure, form well-developed lymphoid follicles, and are reported to senesce. Lymphoid follicles that are induced concurrently with chronic inflammation are more appropriately considered TLS but must be differentiated from inflammation in MALT. Less understood is the etiology for formation of lymphoid tissue aggregates in the ciliary body, limbus, or choroid of healthy eyes in animals and humans. In the healthy eustachian tube and middle ear of animals and humans, MALT may be present but is infrequently described. Concurrent with otitis media, lymphoid follicles in the eustachian tube are probably expanded MALT, but lymphoid follicles in the middle ear may be TLS. The purpose of this comparative review is to familiarize toxicologic pathologists with MALT in the special senses and to provide considerations for differentiating and reporting eye and ear MALT from immune or inflammatory cell infiltrates or inflammation in nonclinical studies, and the circumstances for reporting TLS in compartments of the eye and ear.

Interleukin-13 maintains the stemness of conjunctival epithelial cell cultures prepared from human limbal explants

To use human limbal explants as an alternative source for generating conjunctival epithelium and to determine the effect of interleukin-13 (IL-13) on goblet cell number, mucin expression, and stemness. Human limbal explants prepared from 17 corneoscleral rims were cultured with or without IL-13 (IL-13+ and IL-13-, respectively) and followed up to passage 2 (primary culture [P0]-P2). Cells were characterized by alcian blue/periodic acid-Schiff (AB/PAS) staining (goblet cells); immunofluorescent staining for p63α (progenitor cells), Ki-67 (proliferation), MUC5AC (mucin, goblet cells), and keratin 7 (K7, conjunctival epithelial and goblet cells); and by quantitative real-time polymerase chain reaction for expression of the p63α (TP63), MUC5AC, MUC4 (conjunctival mucins), K3, K12 (corneal epithelial cells), and K7 genes. Clonogenic ability was determined by colony-forming efficiency (CFE) assay. Using limbal explants, we generated epithelium with conjunctival phenotype and high viability in P0, P1, and P2 cultures under IL-13+ and IL-13- conditions, i.e., epithelium with strong K7 positivity, high K7 and MUC4 expression and the presence of goblet cells (AB/PAS and MUC5AC positivity; MUC5AC expression). p63α positivity was similar in IL-13+ and IL-13- cultures and was decreased in P2 cultures; however, there was increased TP63 expression in the presence of IL-13 (especially in the P1 cultures). Similarly, IL-13 increased proliferative activity in P1 cultures and significantly promoted P0 and P1 culture CFE. IL-13 did not increase goblet cell number in the P0-P2 cultures, nor did it influence MUC5AC and MUC4 expression. By harvesting unattached cells on day 1 of P1 we obtained goblet cell rich subpopulation showing AB/PAS, MUC5AC, and K7 positivity, but with no growth potential. In conclusion, limbal explants were successfully used to develop conjunctival epithelium with the presence of putative stem and goblet cells and with the ability to preserve the stemness of P0 and P1 cultures under IL-13 influence.

Neutrophil and T-Cell Homeostasis in the Closed Eye

Purpose

This study sought to examine the changes and phenotype of the tear neutrophil and T-cell populations between early eyelid closure and after a full night of sleep.

Methods

Fourteen healthy participants were recruited and trained to wash the ocular surface with PBS for at-home self-collection of ocular surface and tear leukocytes following up to 1 hour of sleep and a full night of sleep (average 7 hours), on separate days. Cells were isolated, counted, and incubated with fluorescently labeled antibodies to identify neutrophils, monocytes, and T cells. For neutrophil analysis, samples were stimulated with lipopolysaccharide (LPS) or calcium ionophore (CaI) before antibody incubation. Flow cytometry was performed.

Results

Following up to 1 hour of sleep, numerous leukocytes were collected (2.6 × 105 ± 3.0 × 105 cells), although significantly (P < 0.005) more accumulated with 7 hours of sleep (9.9 × 105 ± 1.2× 106 cells). Neutrophils (65%), T cells (3%), and monocytes (1%) were identified as part of the closed eye leukocyte infiltration following 7 hours of sleep. Th17 cells represented 22% of the total CD4+ population at the 7-hour time point. Neutrophil phenotype changed with increasing sleep, with a downregulation of membrane receptors CD16, CD11b, CD14, and CD15, indicating a loss in the phagocytic capability of neutrophils.

Conclusions

Neutrophils begin accumulating in the closed eye conjunctival sac much earlier than previously demonstrated. The closed eye tears are also populated with T cells, including a subset of Th17 cells. The closed eye environment is more inflammatory than previously thought and is relevant to understanding ocular homeostasis.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

The association of lacrimal gland inflammation with alopecia areata

PURPOSE

To describe the association of lacrimal gland inflammation with alopecia areata.

METHODS

We reviewed the medical records of 4 patients diagnosed with lacrimal gland inflammation who had an antecedent or subsequent episode of alopecia. Data was collected on the presentation age, gender, medical history, disease onset, symptoms and signs, imaging, histopathology, systemic evaluation, management and outcome. Pathology and imaging results were correlated with clinical findings.

RESULTS

Three patients were Asian and one Caucasian. Two developed alopecia after presentation for lacrimal inflammation. The remaining two had a history of alopecia totalis (2 years and 10 years). Three of the 4 patients presented or developed other systemic disorders, including seizures, thrombocytopenia, optic neuritis, ulcerative colitis, allergic rhinitis, lymphadenopathy, vasculitic rash and positive p-ANCA values. All received oral corticosteroids, with the addition of methotrexate therapy in one for relapsing inflammation.

CONCLUSIONS

Lacrimal gland inflammation and alopecia areata are autoimmune processes that can be seen in association with each other.

Ocular Mucosal Immunity

Mucosal immunity defends the ocular surface against antigenic challenge and microbial invasion. The principal effector site is the lacrimal gland, where immunoglobulin A (IgA) antibodies are produced. Nasal-associated lymphoid tissue and posterior cervical lymph nodes function as major inductive sites for tear IgA responses. Neural connections and systemic hormones maintain the integrity and function of the ocular surface. Neuroenzyme activities in the lacrimal gland are influenced by ocular infections, leading to reduced expression of acetylcholine and modulation of receptors on acinar cells and on plasma cells, thereby decreasing fluid and immunoglobulin secretion. T lymphocyte-dependent responses result in production of interleukin-4 in lacrimal glands, thereby influencing cholinergic enzyme activity affecting immune processes and lacrimal physiology. Furthermore, neuropeptides released into lymphoid structures or inflamed tissues are chemotactic for antigen-presenting cells and affect their interactions with T cells. Thus, in developing therapeutic approaches for treating dry-eye conditions and vaccination strategies to elicit protective ocular mucosal immune responses, the entire lacrimal functional unit should be considered.

Topographical distribution and characterization of epithelial cells and intraepithelial lymphocytes in the human ocular mucosa

The conjunctiva plays a key role in the protection of the ocular surface by initiating and regulating immune responses. In this study, we analyze the relative proportion of intraepithelial lymphocytes (IELs), apoptotic cells, and proliferative state in three different topographical regions of the normal human conjunctiva. Superior tarsal, superior bulbar, and inferior tarsal-bulbar-fornical conjunctival cells were collected by brush cytology from 63 healthy donors. Flow cytometry analysis showed higher levels of CD3⁺ and CD8⁺ IELs in both upper tarsal and bulbar conjunctiva than in the inferior tarsal-bulbar-fornix, where the CD19⁺ B cells were increased. For all zones two different cell populations (by cell size and complexity) were present in the apoptosis assay. The more complex cells were reduced within the inferior tarsal-bulbar-fornix when compared with the superior bulbar and tarsal areas. Less complex cells were more predominant in the inferior conjunctiva and were mainly alive. The mean proliferation index of the conjunctival epithelium was significantly lower in the superior bulbar conjunctiva than in superior tarsal and inferior fornical conjunctivas. These findings suggest that each topographical zone from normal human conjunctiva has a unique profile of immunophenotype, viability, and proliferative state that could be related to a differentiated regional functionality.

NK cells promote Th-17 mediated corneal barrier disruption in dry eye

BACKGROUND

The conjunctiva contains a specialized population of lymphocytes that reside in the epithelium, named intraepithelial lymphocytes (IEL).

METHODOLOGY/PRINCIPAL FINDINGS

Here we characterized the IEL population prior to and after experimental desiccating stress (DS) for 5 or 10 days (DS5, DS10) and evaluated the effect of NK depletion on DS. The frequency of IELs in normal murine conjunctiva was CD3(+)CD103(+) (~22%), CD3(+)γδ(+) (~9.6%), CD3(+)NK(+) (2%), CD3(-)NK(+) (~4.4%), CD3(+)CD8α (~0.9%), and CD4 (~0.6%). Systemic depletion of NK cells prior and during DS led to a decrease in the frequency of total and activated DCs, a decrease in T helper-17(+) cells in the cervical lymph nodes and generation of less pathogenic CD4(+)T cells. B6.nude recipient mice of adoptively transferred CD4(+)T cells isolated from NK-depleted DS5 donor mice showed significantly less corneal barrier disruption, lower levels of IL-17A, CCL20 and MMP-3 in the cornea epithelia compared to recipients of control CD4(+)T cells.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results show that the NK IELs are involved in the acute immune response to desiccation-induced dry eye by activating DC, which in turn coordinate generation of the pathogenic Th-17 response.

Homeostatic control of conjunctival mucosal goblet cells by NKT-derived IL-13

Although the effects of the interleukin 13 (IL-13) on goblet cell (GC) hyperplasia have been studied in the gut and respiratory tracts, its effect on regulating conjunctival GC has not been explored. The purpose of this study was to determine the major IL-13-producing cell type and the role of IL-13 in GC homeostasis in normal murine conjunctiva. Using isolating techniques, we identified natural killer (NK)/natural killer T (NKT) cells as the main producers of IL-13. We also observed that IL-13 knockout (KO) and signal transducer and activator of transcription 6 knockout (STAT6KO) mice had a lower number of periodic acid Schiff (PAS)+GCs. We observed that desiccating stress (DS) decreases NK population, GCs, and IL-13, whereas it increases interferon-γ (IFN-γ) mRNA in conjunctiva. Cyclosporine A treatment during DS maintained the number of NK/NKT cells in the conjunctiva, increased IL-13 mRNA in NK+ cells, and decreased IFN-γ and IL-17A mRNA transcripts in NK+ and NK- populations. C57BL/6 mice chronically depleted of NK/NKT cells, as well as NKT cell-deficient RAG1KO and CD1dKO mice, had fewer filled GCs than their wild-type counterparts. NK depletion in CD1dKO mice had no further effect on the number of PAS+ cells. Taken together, these findings indicate that NKT cells are major sources of IL-13 in the conjunctival mucosa that regulates GC homeostasis.

Effect of chronic topical glaucoma medications on aerobic conjunctival bacterial flora

PURPOSE

To investigate whether the chronic topical medications affect aerobic conjunctival bacterial flora of patients with glaucoma and to compare their findings with the findings of the controls.

METHODS

Eighty-one patients and 67 healthy control subjects participated in this case-control study. Duplicate conjunctival swab specimens were collected from each patient at the microbiology laboratory and were investigated for the presence of aerobic bacteria. All bacterial species from isolated colonies were identified.

RESULTS

Thirty seven (45.7%) of the 81 patients and 25 (37.3%) of 67 controls had positive conjunctival cultures. Coagulase-negative Staphylococcus was the most commonly isolated bacterial species in both groups. There were no statistically significant differences between the prevalence of other conjunctival cultures testing positive for any of the isolated organisms. The patients were also evaluated with respect to the presence of a systemic illness. Age, sex, presence of diabetes and asthma, duration of antiglaucomatous medication, and number of medications used did not have an effect on culture positivity in both groups when evaluated by logistic regression model.

CONCLUSIONS

The conjunctival culture positivity was higher in patients with glaucoma than in the healthy controls and in patients with diabetes than in patients without diabetes, although both were statistically insignificant. Aerobic conjunctival flora of the patients using topical glaucoma medications and the controls did not differ. Further studies are needed to comment on the clinical importance of these findings.

Both Th1 and Th17 are immunopathogenic but differ in other key biological activities

The role of Th17 lymphocytes in immunopathogenic processes has been well established, but little is known about their basic cell features. In this study, we compared polarized Th1 and Th17 for key biological activities related to pathogenicity and trafficking. Th1 and Th17 lineages were derived from TCR-transgenic CD4 murine cells specific against hen egg lysozyme. When adoptively transferred into mice expressing hen egg lysozyme in their eyes, both Th1 and Th17 induced ocular inflammation but with slight differences in histological pathology. PCR analysis revealed selective expression of IFN-gamma or IL-17 in eyes of Th1 or Th17 recipients, respectively. Additionally, Th1 and Th17 were found to differ in three other key activities: 1) Th17 cells were inferior to Th1 cells in their capacity to trigger massive lymphoid expansion and splenomegaly; 2) the proportion of Th1 cells among infiltrating cells in inflamed recipient eyes declined rapidly, becoming a minority by day 7, whereas Th17 cells remained in the majority throughout this period; and 3) remarkable differences were noted between Th1 and Th17 cells in their expression of certain surface markers. In particular, reactivated Th1 expressed higher levels of CD49d and alpha(4)beta(7) (mucosal homing) in vitro and higher levels of CXCR3 (Th1 trafficking) in vivo. Reactivated Th17, however, expressed higher levels of alpha(E)beta(7) (epithelial tissue homing) and CD38 (activation, maturation and trafficking) in vitro, but in vivo Th17 expressed higher levels of alpha(4)beta(7) and CCR6 (lymphocyte trafficking). These data reveal that Th1 and Th17 cells differ in several key biological activities influencing migration and pathogenic behavior during inflammatory disease.

Influence of the eye-associated lymphoid tissue (EALT) on inflammatory ocular surface disease

Certain similarities exist in the pathophysiological processes and clinical features of advanced stages of various inflammatory ocular surface diseases, suggesting that common pathways contribute to these diseases. In this article, common pathways are analyzed with a focus on the role of the physiological resident mucosal immune system of the ocular surface, termed eye-associated lymphoid tissue (EALT). This is physiologically protective but if it is deregulated it can mediate an inflammatory immune answer. Common events in inflammatory ocular surface disease lead to a vicious circle of immune-modulated inflammation, with degenerative remodeling and loss of function.

Drainage of tears: impact on the ocular surface and lacrimal system

The human efferent tear ducts are part of the lacrimal system. Because little knowledge exists concerning the physiology of the nasolacrimal system, and hence its patho- physiology, the nasolacrimal system has received almost no consideration as a possible factor in dry eye. The human nasolacrimal ducts consist of the upper and the lower lacrimal canaliculus, the lacrimal sac, and the nasolacrimal duct. As a draining and secretory system, the efferent tear ducts play a role in tear transport and nonspecific immune defense. Moreover, components of tear fluid are absorbed in the nasolacrimal passage and are transported into a surrounding vascular system. This system is similar to a cavernous body that is subject to autonomic control and regulates tear outflow. Tear duct-associated lymphoid tissue (TALT) is present in the efferent tear ducts, displaying the cytomorphological and immunophenotypic features of mucosa-associated lymphoid tissue (MALT). Under normal conditions, tear fluid components are constantly absorbed into the blood vessels of the surrounding cavernous body. These vessels are connected to the blood vessels of the outer eye and could act as a feedback signal for tear fluid production, which ceases if these tear components are not absorbed. In this way, dry eye could be initiated. Defective stimulation of TALT could result in abnormal immune deviation at the ocular surface, leading to an autoimmunological response that causes dry eye pathology.

Effect of inflammation on lacrimal gland function

The lacrimal gland is the main contributor to the aqueous layer of the tear film. It secretes proteins, electrolytes and water, which helps to nourish and protect the ocular surface. Lacrimal gland secretion is primarily under neural control, which is achieved through a neural reflex arc. Stimuli to the ocular surface activate afferent sensory nerves in the cornea and conjunctiva. This in turn activates efferent parasympathetic and sympathetic nerves in the lacrimal gland to stimulate secretion. Sex steroid hormones are also important regulators of lacrimal gland functions. A decrease or lack of lacrimal gland secretion is the leading cause of aqueous tear deficient dry eye syndrome (DES). It has been suggested that DES is an inflammatory disorder that affects the ocular surface and the lacrimal gland. In several pathological instances, the lacrimal gland can become a target of the immune system and show signs of inflammation. This can result from autoimmune diseases (Sjögren's syndrome), organ transplantation (graft versus host disease), or simply as a result of aging. The hallmarks of lacrimal gland inflammation are the presence of focal lymphocytic infiltrates and increased production of proinflammatory cytokines. The mechanisms leading to lacrimal gland dysfunction are still poorly understood. Apoptosis, production of autoantibodies, hormonal imbalance, alterations in signaling molecules, neural dysfunction, and increased levels of proinflammatory cytokines have been proposed as possible mediators of lacrimal gland insufficiency in disease states.

Cell populations and adhesion molecules expression in conjunctiva before and after bone marrow transplantation

We were interested to analyse the composition of the cellular infiltrate and adhesion molecules expression in the conjunctiva before and at least one hundred days after autologous and allogenic bone marrow transplantation (BMT) and its relation with the presence of dry eye. We used immunohistochemistry on cryopreserved human conjunctiva with monoclonal antibodies to T-lymphocytes (CD3, CD4 and CD8), B-lymphocytes (CD19), macrophages (CD14), natural killer cells (NK, CD57), intercellular adhesion molecule 1 (ICAM-1), E-selectin, vascular cell adhesion molecule-1 (VCAM-1), lymphocyte function associated antigen-1 (LFA-1), very late antigen-4 (VLA-4), interleukin 2 receptor (IL2r, CD25) and HLA-DR. Our autologous recipients had no graft-versus-host disease (GVHD) but allogenic patients had chronic GVHD. After autologous BMT the conjunctiva had significantly more: (1) T lymphocytes (CD3+, CD4+, CD8+) in the epithelium; (2) CD4+ and CD14+ cells in the stroma; and (3) VLA-4 expression in the stroma than before BMT. After allogenic BMT, the conjunctiva exhibited a significant increase of: (1) CD3+ and CD14+ cells in the epithelium; (2) T lymphocytes (CD3+, CD4+, CD8+) and CD14+ cells in the stroma; and (3) VLA-4 and LFA-1 expression in the stroma than before BMT. After the engraftment, the comparison between autologous and allogenic recipients revealed that: (1) there were no significant differences in adhesion molecule expression; (2) the epithelium of autologous recipients had significantly more CD3+ cells; and (3) the stroma of allogenic patients had significantly more CD3+ and CD8+ cells. Among allogenic recipients, CD14+ cells were significantly increased both in the epithelium and in the stroma of patients with signs or symptoms of dry eye in comparison with patients without ocular involvement. Additionally, those having keratoconjunctivitis sicca (KCS) had CD4/CD8 ratios significantly higher than those without KCS. In conclusion, in the conjunctiva after autologous BMT a subclinical cell mediated immune reaction seems to take place. The conjunctivitis of chronic GVHD is complex, with T cells and macrophages dramatically contributing to the process.

The role of eye-associated lymphoid tissue in corneal immune protection

Because the cornea is optimized for refraction, it relies on supporting tissues for moistening and nutrition and in particular for immune protection. Its main support tissue is the conjunctiva, in addition to the lacrimal gland, the latter which provides soluble mediators via the tear film. The cornea and conjunctiva constitute a moist mucosal surface and there is increasing evidence that apart from innate defence mechanisms, also lymphoid cells contribute to the normal homeostasis of the corneal surface. A Medline-based literature search was performed in order to review the existing literature on the existence, composition and functions of mucosa-associated lymphoid tissue (MALT) at the ocular surface for corneal protection. The existence of lymphoid cells at the ocular surface and appendage has been known for many years, but for a long time they were believed erroneously to be inflammatory cells. More recent research has shown that in addition to the known presence of lymphoid cells in the lacrimal gland, they also form MALT in the conjunctiva as conjunctiva-associated lymphoid tissue (CALT) and in the lacrimal drainage system as lacrimal drainage-associated lymphoid tissue (LDALT). Together this constitutes an eye-associated lymphoid tissue (EALT), which is a new component of the mucosal immune system of the body. When the topographical distribution of CALT is projected onto the ocular surface, it overlies the cornea during eye closure and is hence in a suitable position to assist the corneal immune protection during blinking and overnight. It can detect corneal antigens and prime respective effector cells, or distribute protective factors as secretory IgA.

[Dry eye disease as a complex dysregulation of the functional anatomy of the ocular surface. New concepts for understanding dry eye disease]

INTRODUCTION

Dry eye disease is a disorder of the tear film that results in epithelial damage and in a disruption of the normal homeostasis at the ocular surface. It is widespread and causes symptoms ranging from discomfort to blindness.

METHODS

A review of the existing literature was used to compare different past and recent concepts for the understanding of dry eye disease with a focus on aspects of the integrating functional anatomy of the ocular surface.

RESULTS

The understanding of the pathogenesis of dry eye disease has proceeded from the mere recognition of a lack of tears to a consideration of their quality and to the concept of wetting of the ocular surface. However, several other aspects as epithelial differentiation, innervation, hormonal status or immune protection contribute to the intact functional anatomy of the ocular surface. Recently it has been recognized that immunologically regulated mechanisms of inflammation represent a primary or secondary pathogenetic factor for dry eye disease. This is conceivably regulated by the cells of the physiological mucosal immune defence system, the eye-associated lymphoid tissue (EALT). Androgens represent an important trophic factor for the ocular surface and their deficiency predisposes to inflammation.

CONCLUSION

Dry eye disease represents a complex dysregulation of the functional anatomy of the ocular surface that can start from different alterations (e.g. insufficient secretion, defects in wetting or innervation). Immune-based inflammation is able to interconnect and negatively reinforce these different pathomechanisms, resulting in a vicious circle.

[Eye-associated lymphoid tissue (EALT) is continuously spread throughout the ocular surface from the lacrimal gland to the lacrimal drainage system]

INTRODUCTION

Components of the mucosal immune system (MALT) have been identified in the conjunctiva (as CALT) and the lacrimal drainage system (as LDALT). Their structural and functional relation with the established immune protection by the lacrimal gland is unclear.

MATERIAL AND METHODS

Macroscopically normal and complete tissues of the conjunctiva, lacrimal drainage system and lacrimal gland from human body donors were investigated by analysis of translucent whole mounts, and using histology, immunohistology as well as scanning and transmission electron microscopy.

RESULTS

A typical diffuse lymphoid tissue, composed of effector cells of the immune system (T-lymphocytes and IgA producing plasma cells) under an epithelium that contains the IgA transporter SC, is not isolated in the conjunctiva and lacrimal drainage system. It is anatomically continuous from the lacrimal gland along its excretory ducts into the conjunctiva and from there via the lacrimal canaliculi into the lacrimal drainage system. Lymphoid follicles occur in a majority (about 60%) and with bilateral symmetry. The topography of CALT corresponds to the position of the cornea in the closed eye.

CONCLUSION

These results show that the MALT of the lacrimal gland, conjunctiva and lacrimal drainage system constitute an anatomical and functional unit for immune protection of the ocular surface. Therefore it should be integrated as an "eye-associated lymphoid tissue" (EALT) into the MALT system of the body. EALT can detect ocular surface antigens by the lymphoid follicles and can supply other organs and the ocular surface including the lacrimal gland with specific effector cells via the regulated recirculation of lymphoid cells.

Ocular surface epithelium induces expression of human mucosal lymphocyte antigen (HML-1) on peripheral blood lymphocytes

BACKGROUND/AIMS

Peripheral blood CD8+ lymphocytes that home to mucosal surfaces express the human mucosal lymphocyte antigen (HML-1). At mucosal surfaces, including the ocular surface, only intraepithelial CD8+ lymphocytes express HML-1. These lymphocytes are retained in the intraepithelial compartment by virtue of the interaction between HML-1 and its natural ligand, E-cadherin, which is expressed on epithelial cells. The purpose of this study was to determine whether ocular surface epithelial cells (ocular mucosa) could induce the expression of human mucosal lymphocyte antigen on peripheral blood lymphocytes.

METHODS

Human corneal and conjunctival epithelial cells were co-cultured with peripheral blood lymphocytes. Both non-activated and activated lymphocytes were used in the experiments. After 7 days of incubation, lymphocytes were recovered and analysed for the antigens CD8/HML-1, CD4/HML-1, CD3/CD8, CD3/CD4, CD3/CD25, CD8/CD25, and CD4/CD25 by flowcytometry.

RESULTS

Significant statistical differences were observed in the CD8/HML-1 expression when conjunctival epithelial cells were co-cultured with non-activated and activated lymphocytes (p = 0.04 for each) and when corneal epithelial cells were co-cultured with non-activated lymphocytes (p = 0.03). Significant statistical difference in CD4/HML-1 expression was observed only when conjunctival epithelial cells were co-cultured with activated lymphocytes (p = 0.02).

CONCLUSION

Ocular surface epithelial cells can induce the expression of human mucosal lymphocyte antigen on CD8+ (and to some extent on CD4+) lymphocytes. This may allow the retention of CD8+ and CD4+ lymphocytes within the epithelial compartment of the conjunctiva and play a part in mucosal homing of lymphocytes.

Development of organised conjunctival leucocyte aggregates after corneal transplantation in rats

AIM

To investigate the development of lymphoid aggregates in the conjunctiva after corneal transplantation in rats.

METHODS

LEW or PVG strain corneas were transplanted orthotopically to PVG rats. Cornea and conjunctiva were examined clinically for up to 42 days. Eyes were removed with attached conjunctiva on days 10 and 15 after transplantation (before and during rejection), together with normal eyes, fixed, paraffin embedded, and examined immunohistochemically.

RESULTS

Clinically, the temporal half of the upper palpebral conjunctiva of recipients of 10/19 allografts and 1/10 isografts developed pronounced swelling, correlating with inflammation and rejection. Histologically, the swelling comprised leucocytic aggregates with an altered overlying epithelium. Aggregates contained granulocytes, macrophages, and cells expressing major histocompatibility complex (MHC) class II, CD4, and CD8, all more numerous in allograft associated conjunctiva. Class II+ cells were more abundant at the surface, whereas macrophages and T cells were more numerous in the deeper stroma. There were few B cells. There was greater CD54 expression by vascular endothelium in allograft associated aggregates. Cells expressing TNFalpha and IFNgamma but not IL1beta were present in stromal and superficial areas.

CONCLUSIONS

Corneal transplantation in rats induces the development of organised conjunctival leucocytic aggregates in a fixed location that are significantly more pronounced in recipients of allografts compared with isografts and show characteristics of a Th1 type immune response. These aggregates have characteristics of conjunctiva associated lymphoid tissue and may be sites of presentation of graft antigens and lymphocyte proliferation at the ocular surface.

Image fusion analysis of 99m Tc-HYNIC-octreotide scintigraphy and CT/MRI in patients with thyroid-associated orbitopathy: the importance of the lacrimal gland

The aim of this study was to describe the anatomical structures that show uptake of the somatostatin analogue octreotide in patients with thyroid-associated orbitopathy (TAO). The study population comprised a series of 20 TAO patients attending the out-patient thyroid clinic and 12 patients presenting head or neck tumours. Scintigraphy was carried out with our newly developed tracer, technetium-99m labelled EDDA-HYNIC-TOC ((99m)Tc-TOC). Morphological imaging was done with either magnetic resonance imaging or X-ray computed tomography without contrast medium. Both imaging procedures were done within an interval of 3-4 weeks. For the image fusion procedure, specific external reference markers were used for each imaging modality. The markers were screwed onto a reference frame, which was held in place via a vacuum-fixed mouthpiece. The anatomical structure showing tracer uptake that was most frequently recognised was the lacrimal gland, followed by the retronasal area, cervical lymph structures, salivary glands, the anterior insertion points of the extra-ocular muscles and discrete areas of the neck extensor muscles. The lacrimal gland and the retronasal area showed the highest and most frequent uptake of (99m)Tc-TOC in TAO patients, whereas such uptake did not occur in the retrobulbar space. In spite of knowledge of these results of image fusion, no changes in the involved structures could be detected on morphological imaging. It is concluded that binding of (99m)Tc-TOC is more frequently localised to the anterior compartment of the eye and to the neck. The previously used term "orbital" uptake should be abandoned and replaced by a descriptive term relating to the anatomically recognised structure showing tracer accumulation, i.e. the lacrimal gland. The uptake of octreotide by lymphoid and salivary glands opens a new field of investigation related to the physiology of somatostatin.

Structural and cellular architecture of conjunctival lymphoid follicles in the baboon (Papio anubis)

Conjunctival lymphoid follicles (CLFs), present in normal individuals, undergo hyperplasia upon conjunctival infection by a specific array of pathogens; infection-associated enlargement of draining preauricular lymph nodes suggests that conjunctival follicles participate in the afferent limb of acquired immune responses for the ocular surface. The present study was performed to delineate the structural and lymphoid anatomy of CLFs in the baboon (Papio anubis), a non-human primate conjunctival model with close similarity to the human. Conjunctiva from both eyes, along with mesenteric lymph node, spleen, tonsil, and ileum controls were harvested from ten baboons at necropsy, and studied by histochemical and immunohistochemical methods. Baboon conjunctival follicles were identified as dense oval collections of leukocytes in the substantia propria with infiltration into a thinned overlying conjunctival epithelium. Goblet cells were universally absent, the overlying mucin layer was attenuated, and the follicle-associated epithelium (FAE) demonstrated comparatively diminished alkaline phosphatase expression. The basement membrane overlying each follicle appeared discontinuous. CD4-positive T lymphocytes were distributed in parafollicular areas and to a lesser degree in follicle germinal centers. B lymphocytes formed the predominant cell in follicles, and also heavily infiltrated the FAE. B cell IgM expression was prominent in germinal centers, while IgD staining occurred in a horseshoe-shaped distribution in the follicle mantle zone. Although B cell IgA expression was noted in the non-follicular conjunctiva, IgA expression was inconspicuous within conjunctival follicles. S-100- and CD1a-positive dendritic cells were found in FAE, while fascin-positive mature dendritic cells appeared in the deeper areas of each follicle. CD68-positive macrophages were dispersed throughout the follicles. CD35-positive follicular dendritic cells were observed only in germinal centers. CLFs appear highly organized consistent with a role in the adaptive immune response to conjunctival pathogens.

Loss of tear duct-associated lymphoid tissue in association with the scarring of symptomatic dacryostenosis

OBJECTIVE

To determine whether organized mucosa-associated lymphoid tissue (MALT) is a normal component of the human efferent tear ducts or is acquired in reaction to chronic inflammation.

DESIGN

Nonrandomized comparative (cadaver controlled) study with histopathologic correlations.

MATERIALS

Tissue specimens from nasolacrimal ducts of 38 patients undergoing endonasal dacryocystorhinostomy in postinflammatory dacryostenosis with signs of chronic inflammation were analyzed using histologic examination and immunohistochemical studies. Only tissue specimens revealing proliferative sclerotic forms of chronic fibrosis were chosen for the study. Eighty specimens from the lacrimal systems of body donors served as controls.

TESTING

Tissue specimens from each lacrimal system were prepared and processed with paraffin, sectioned, stained using different histologic methods with an array of specific antibodies, and examined by light microscopy.

MAIN OUTCOME PARAMETERS

The distribution of intraepithelial and subepithelial defense cells was analyzed to identify plasma cells, secretory immunoglobulins, lymphocytes, dendritic cells, and organized mucosa-associated lymphoid tissue.

RESULTS

The presence of secretory immunoglobulin A was demonstrated in subepithelial plasma cells and in the cytoplasm of apical epithelial cells in both chronically inflamed and healthy lacrimal systems. In more than one third of cases from body donors, but in only a few biopsy specimens from patients, organized lymphoid tissue was found with the cytomorphologic and immunophenotypical features of MALT. All other cases showed a diffuse infiltrate of defense cells within the lamina propria.

CONCLUSIONS

The development of tear duct-associated lymphoid tissue (TALT) is a common feature that is often found in symptomatically normal nasolacrimal ducts. Because TALT seems to be lost associated with the scarring of symptomatic dacryostenosis, it is unlikely that the presence per se of TALT leads to scarring. Future studies are needed to explain the development of TALT.

The conjunctival lymphoid follicle in mucosal immunology

The conjunctiva forms a continuous mucosal surface from the eyelid margin to the cornea, and makes contact with airborne antigens and those on the adjacent eyelid skin and preocular tear film. Conjunctival lymphoid follicles (CLF) undergo hyperplasia upon conjunctival infection by a specific array of pathogens; infection-associated enlargement of draining preauricular lymph nodes suggests that CLF participate in the afferent limb of acquired immune responses for the ocular surface. In this review, we examine the evidence for classification of CLF as part of the common mucosal immune system, and explore the possible therapeutic implications.

Single dose intranasal administration of retinal autoantigen generates a rapid accumulation and cell activation in draining lymph node and spleen: implications for tolerance therapy

BACKGROUND/AIMS

A single intranasal delivery of retinal autoantigen suppresses effectively experimental autoimmune uveoretinitis (EAU). To further unravel underlying mechanisms the authors wished to determine, firstly, the kinetics of antigen delivery and, secondly, the early cellular responses involved in the initial stages of nasal mucosal tolerance induction.

METHODS

Flow cytometry, cell proliferation assays, and microscopy were used to track antigen following a single, intranasal dose of Alexa-488 labelled retinal antigen.

RESULTS

A rapid accumulation of antigen within both superficial cervical lymph nodes (SCLN) and spleen was observed after 30 minutes. Significant proliferative responses to IRBP were elicited by 48 hours indicating that systemic priming of naive T cells to retinal antigen had occurred. Cell activation was further confirmed by immunoprecipitation studies, which demonstrated phosphorylation of STAT4 but not STAT6 in both lymph nodes and spleen. However, at 24 hours, STAT4 heterodimerisation with STAT 3 was only observed in spleen.

CONCLUSIONS

The results provide novel evidence that following a single intranasal application rapid transfer of antigen occurs. Resulting T cell proliferation develops consequent to differential cell signalling in SCLN and spleen. Further understanding of these underlying cellular mechanisms, in particular as is inferred by the results the contribution of local versus systemic tolerance induction, may assist in strategies to clinically apply mucosal tolerance therapy successfully.

Lymphocyte lineages at mucosal effector sites: rat salivary glands

Development of T cell lineages and the role of the thymus as a source of immature T cells in parotid (PG) and submandibular salivary glands (SMG) were studied in Fischer 344 rats using the Thy-1/CD45RC/RT6 expression model. In addition, the phenotypes of salivary gland lymphocytes were compared with other conventional and extrathymic populations. PG mononuclear cells consisted of T cells (38%), B cells (29%), and NK cells (4%). SMG had 19% T cells, 7% B cells, 37% NK cells, and an unusual population of CD3(-)/RT6(+) cells. In comparison with lymph node (LN), both PG and SMG were enriched in immature (Thy-1(+)) and activated (Thy-1(-)/CD45RC(-)/RT6(-)) T cells. Unchanged percentages of Thy-1(+) T cells in PG and SMG following short-term adult thymectomy indicated that immature salivary gland T cells had an extrathymic source. In contrast, thymectomy eliminated LN recent thymic emigrants. SMG had T cells with characteristics of extrathymic populations, expressing TCRgammadelta(+) (28%), the CD8alphaalpha homodimer (11%), and NKR-P1A (66%). Many SMG T cells expressed integrin alpha(E)beta(7). PG T cells resembled those isolated from LN in respect to TCR and CD8 isoform usage, but were enriched in alpha(E)beta(7)(+) T cells and in NKT cells. Thus, salivary gland mononuclear cells are composed of a variety of subpopulations whose distributions differ between SMG and PG and are distinct from LN. These studies provide a basis for further investigation of regionalization in the mucosal immune network and are relevant to the design of vaccine regimens and intervention during pathological immune processes.

Development of T cell lineages in rat lacrimal glands

PURPOSE

The purpose of this study was to examine T cell development in rat lacrimal glands, determine whether the thymus is the source of immature T cells in this tissue and compare lacrimal gland T lymphocytes with other T cell subpopulations.

METHODS

Mononuclear cells were isolated from lacrimal glands of normal or thymectomized female Fischer 344 rats and stained for flow cytometric analysis.

RESULTS

The lacrimal gland T lymphocyte population included large percentages of cells with an activated phenotype and also subpopulations of immature, naive and memory T cells. The numbers of immature (Thy-1(+)) lacrimal gland T cells were unchanged following short-term adult thymectomy. In comparison, spleen had large percentages of naive T cells, only a small subpopulation of activated T cells, and similar percentages of immature (Thy-1(+)) T cells, which were nearly eliminated after thymectomy. Lacrimal gland T cells had small subpopulations of TCRgammadelta(+) and CD8alphaalpha( +) T cells, a large subpopulation of NKT cells and many integrin alphaEbeta7( +) T cells.

CONCLUSIONS

Lacrimal gland T cells are composed of a variety of subpopulations whose composition is distinct from splenocytes. The marked reduction of immature splenic T cell percentages eleven days after adult thymectomy indicates that these cells were mostly derived from thymic precursors. In contrast, the unchanged percentages of immature lacrimal gland T cells following thymectomy indicate that they may have an extrathymic source. These studies provide a foundation for further investigation into the cellular basis of lacrimal gland immunobiology.

Clinical and pathologic findings in human keratolimbal allograft rejection

OBJECTIVE

To characterize the clinical and pathologic features of cadaveric keratolimbal allograft (KLAL) rejection.

DESIGN

The study design is descriptive.

PARTICIPANTS

Four patients (five eyes) with KLAL rejection are reported.

INTERVENTION

All patients were subjected to slit-lamp biomicroscopy, treatment of rejection, and ultimately required repeat KLAL surgery. In three patients (four eyes), specimens obtained at the time of repeat surgery were subjected to immunohistochemical staining against the following immune and surface human antigens: CD4, CD8, CD19, CD3, DR, CK19, CK3, and vimentin.

RESULTS

Signs of allograft rejection included intense sectoral injection, diffuse or perilimbal conjunctival injection, edema, and infiltration of the KLAL grafts, leading to punctate epithelial erosions, epithelial defects, and surface keratinization. Rejected specimens revealed T-lymphocyte infiltration (CD4:CD8, 2:1) with strong HLA-DR (MHC class II) expression. The epithelium stain results were positive for cytokeratin 19 and weakly positive to absent for cytokeratin 3. The epithelial stain results were weakly positive for vimentin in only one specimen.

CONCLUSIONS

KLAL rejection is a newly recognized entity. Pathologic findings of rejected specimens indicate that this is a T-cell mediated rejection phenomenon. The pattern of cytokeratin staining provided little evidence that the epithelium covering KLALs had a corneal phenotype. The scarcity of vimentin-positive epithelial cells suggests that the stem-cell/transient-cell pool was probably depleted. Early recognition of clinical rejection is important, as treatment with immunosuppressive therapy may reverse the process.

In vivo behavior of peptide-specific T cells during mucosal tolerance induction: antigen introduced through the mucosa of the conjunctiva elicits prolonged antigen-specific T cell priming followed by anergy

The mucosa of the conjunctiva is an important site of entry for environmental Ags as well as Ags emanating from the eye itself. However, very little is known about T cell recognition of Ag introduced through this important mucosal site. We have characterized the in vivo process of CD4 T cell recognition of Ag delivered via the conjunctival mucosa. Application of soluble OVA to the conjunctiva of BALB/c mice induced potent T cell tolerance. APC-presenting OVA peptide in vivo was only found in the submandibular lymph node and not in other lymph nodes, spleen, or nasal-associated lymphoid tissue. Similarly, in TCR transgenic DO11. 10 adoptive transfer mice, OVA-specific CD4+ T cell clonal expansion was only observed in the submandibular lymph node following conjunctival application of peptide. These experiments thus define a highly specific lymphatic drainage pathway from the conjunctiva. OVA-specific T cell clonal expansion peaked at day 3 following initiation of daily OVA administration and gradually declined during the 10-day treatment period, but remained elevated compared with nontreated adoptive transfer mice. During this period, the T cells expressed activation markers, and proliferated and secreted IL-2 in vitro in response to OVA stimulation. In contrast, these cells were unable to clonally expand in vivo, or proliferate in vitro following a subsequent OVA/CFA immunization. These results suggest that Ag applied to a mucosal site can be efficiently presented in a local draining lymph node, resulting in initial T cell priming and clonal expansion, followed by T cell anergy.

Human conjunctiva contains high endothelial venules that express lymphocyte homing receptors

Lymphocyte trafficking into tissues has been shown to occur across vessels with specialized endothelial cells called high endothelial venules. High endothelial venules naturally occur in lymph nodes and mucosal lymphoid tissues. The presence of high endothelial venules in the conjunctiva has not been demonstrated previously and the purpose of this study was to determine whether there is such a specialized vasculature to facilitate lymphocyte trafficking in conjunctiva associated lymphoid tissue.Samples of conjunctiva from four different individuals were analysed morphometrically for the presence of high endothelial venules by light and electron microscopy, and by immunohistochemistry using antibodies specific for high endothelial venules and for two adhesion molecules namely, Vascular Adhesion Protein-1 and Mucosal Addressin Cell Adhesion Molecule-1, expressed on high endothelial venules found in other tissues. Blood vessels with anatomical features of high endothelial venules were demonstrated in relation to conjunctival follicles and in the lamina propria. Immunohistochemical studies showed positive staining of vessels with anti-high endothelial venule antibodies, and with antibody against Vascular Adhesion Protein-1 but not with antibody against Mucosal Addressin Cell Adhesion Molecule-1. This study reveals that some of the blood vessels associated with conjunctival follicles and lamina propria have features of high endothelial venules. These vessels may play a significant role in lymphocyte homing to the conjunctiva and Vascular Adhesion Protein-1 (but not Mucosal Addressin Cell Adhesion Molecule-1) is one of the vascular addressin/adhesion molecules.

Lymphocyte subsets in conjunctival mucosa-associated-lymphoid-tissue after exposure to retinal-S-antigen

PURPOSE

To evaluate the immune cell subsets in conjunctival mucosa-associated-lymphoid-tissue (C-MALT) following challenge with antigen.

METHODS

Ten adult female Lewis rats were studied. Five rats received one drop (5 microL) of retinal S-antigen (500 microg/mL in phosphate buffered saline, PBS) instilled into the lower fornix twice daily for 10 consecutive days. Five rats received PBS only and served as controls for the experiment. Two days after the last instillation the animals were sacrificed and the orbital contents prepared for immunohistological staining. A panel of monoclonal antibodies was used: CD5, CD4, CD8, CD25, and CD45RA. The number of positive cells were counted in sections of epibulbar, forniceal, and tarsal conjunctiva.

RESULTS

There was a significant increase in the number of CD8+ T lymphocytes in the conjunctiva of animals receiving retinal S-antigen when compared to control animals.

CONCLUSION

Conjunctival instillation of retinal S-antigen causes an immune response in the C-MALT with a significant increase in the CD8+ T lymphocyte subset in this tissue. This response may be involved in the induction of tolerance to the encountered antigen.

Antimicrobial defensin peptides of the human ocular surface

BACKGROUND/AIMS

The antimicrobial activity of the tear film exceeds the activity of its known constituents. The authors postulate that this excess activity is the result of antimicrobial peptides called defensins, and they aimed to look for defensins in the human eye.

METHODS

Evidence of defensin production was sought by reverse transcriptase polymerase chain reaction (RT-PCR). Intron spanning primers were designed for beta defensins 1 and 2, and alpha defensins 5 and 6. RT-PCR was performed on cornea, conjunctiva, and lacrimal gland samples, and reaction products were size fractionated and sequenced to confirm their identity. A monoclonal antibody was utilised for the detection of alpha defensins 1, 2, and 3 in tissue sections and in immunoblots of tears.

RESULTS

RT-PCR revealed beta defensin 1 message in samples of conjunctiva, cornea, and lacrimal gland. beta Defensin 2 message was detected in the conjunctiva and cornea but was absent from the lacrimal gland. alpha Defensin 5 and 6 message was absent in these tissues but alpha defensins 1, 2, and 3 were detected in normal tears, lacrimal gland, and inflamed conjunctiva by immunochemistry.

CONCLUSION

The data suggest the human eye innately produces a spectrum of antimicrobial defensin peptides. Defensins hold therapeutic potential in ocular infections as they have a broad spectrum of antimicrobial activity (bacteria fungi and viruses ) and accelerate epithelial healing.

Intranasal administration of retinal antigens induces transient T cell activation and apoptosis within drainage lymph nodes but not spleen

Mechanisms of mucosal tolerance induction, including anergy/deletion and active suppression are frequently described as mutually exclusive; dependent upon nature, dose and route of antigen administration. We have previously described induction of low-dose tolerance with administration of retinal autoantigens via the nasorespiratory tract which is antigen-specific, suppresses both cell mediated immunity and ultimately tissue destruction in experimental autoimmune uveoretinitis (EAU) and is mediated by splenic-derived regulatory cells. The present data further shows that splenocytes or fractionated splenic T cells, which secrete IL-4 and IL-10 when stimulated with retinal antigen in vitro, and not regional drainage lymph node cells transfer tolerance to naïve animals. Analysis of apparent mechanistic differences shows that during intranasal antigen administration, the proportion of CD4(+)T cells within drainage lymph nodes increases, concurrent with a burst of IFN-gamma. Following subsequent antigen challenge, T cells downregulate alphabetaTCR expression and undergo apoptosis in regional drainage lymph nodes. An increase in functional Th2 cytokine activity was noted in both Con-A and retinal antigen stimulated lymph node cultures in tolerized animals. T cells from tolerized animals secreted IL-4, whereas IL-10 was secreted predominantly by the non-T cell population present equally in control and tolerized animals. Therefore, spleen derived regulatory cells which suppress Th1 responses and T cell deletion/apoptosis in regional drainage lymph nodes are mechanisms which co-exist in tolerant rats. Th2 cytokine production after immunization appears consequential to tolerance-induced Th1 suppression.

Prolonged survival of corneal allografts incubated in alloantibody fragments

BACKGROUND

In this study, we determined the binding characteristics of F(ab')2 alloantibody fragments to corneal antigens and assessed the capacity of these antibody fragments to protect corneal allografts from immune attack.

METHODS

Goat anti-rabbit alloantibodies were pepsin-digested and labeled with 125I, and the time course of association and dissociation of the F(ab')2 fragments was determined. Corneal allografts were incubated in unlabeled F(ab')2 fragments and transplanted into allogeneic recipients, and the graft survival times were recorded.

RESULTS

Binding of radiolabeled F(ab')2 fragments to rabbit cornea cells reached a maximum at 12 hr. At 32 degrees C (rabbit corneal temperature), the radiolabel eluted rapidly from the cornea, reaching baseline at 72 hr. At 4 degrees C (corneal graft storage temperature), significant amounts remained associated with the cornea at 96 hr. Mean survival time for grafts incubated in F(ab')2 anti-rabbit fragments was significantly greater than that of grafts incubated in nonimmune F(ab')2 fragments. Three of the corneal allografts incubated in goat F(ab')2 anti-rabbit fragments survived for 100 days, whereas the longest surviving control allograft incubated in goat F(ab')2 nonimmune fragments was rejected on day 24. Preincubation of corneas in unlabeled, immune F(ab')2 fragments followed by incubation in radiolabeled, immune F(ab')2 fragments suggested that antigen masking was not a factor in the prolongation of graft survival.

CONCLUSION

Based on the binding and release kinetics and the graft survival times, it appears that the protective effect of immune F(ab')2 fragments extends well beyond the binding interval of the antibody fragments to corneal cell membranes.

Comparative anatomy of mammalian conjunctival lymphoid tissue: a putative mucosal immune site

Organized mucosa-associated lymphoid tissue (O-MALT) is defined by mucosal lymphoid follicles with unique overlying lymphoepithelia, and classically appears in tissues with a simple columnar epithelium. Within follicle-associated epithelium, goblet cells are characteristically absent, replaced by ultrastructurally distinct antigen-absorptive cells, termed M cells (or microfold cells) for the appearance of their apical cell membranes. To determine if mammalian conjunctiva, with its stratified squamous epithelium, can be considered as a site of O-MALT, we compared the light and electron microscopic anatomy of conjunctiva from fourteen species of non-human adult mammals, and the conjunctiva of human adults harvested at autopsy. Lymphoid follicles in the conjunctiva were demonstrated in all mammals studied except for mice and rats. In those mammals with conjunctival lymphoid follicles, the follicle-associated conjunctival epithelium was notable for an absence of goblet cells. Transmission electron microscopy demonstrated an intimate association of lymphocytes with surface epithelial cells, but epithelial cell morphology was uniform overlying the follicle, and other ultrastructural features of M cells were absent. Therefore, conjunctival lymphoid follicle-associated stratified squamous epithelium demonstrates some but not all features of O-MALT lymphoepithelia. Further studies are necessary to determine what role conjunctival lymphoid tissue may play in mucosal immunity.

Anatomy of mammalian conjunctival lymphoepithelium

Ocular surface immune mechanisms are subservient to the fine function of the eye. A clear cornea with a smooth, well-lubricated facade is prerequisite to lucid vision. Hence, corneal inflammation and post-inflammatory scarring are intolerable, and the cornea contains a minimum of lymphoid elements. Although conjunctival dysfunction and consequent tear film deficiency can malign the corneal surface, conjunctival inflammation is tolerated to a considerable degree. In contrast to the human cornea, human conjunctiva contains an abundance of lymphoid tissue. Certain aspects of human conjunctival immunology elicit little debate. Langerhans cells are abundant in conjunctival epithelium. Isolated CD8+ suppressor/cytotoxic T cells predominate in conjunctival epithelium, while T cells in the substantia propria distribute equally between CD4+ T helper cells and CD8+ cells. Yet the presence of plasma cells in human conjunctiva, the expression of secretory component by human conjunctival epithelium, and the function of human conjunctival lymphoid follicles are in dispute. Confusion may derive in part from the use of inappropriate animal models; rodent conjunctiva does not appear to be a worthy facsimile for human conjunctiva. Discrepancies between different human studies likely result from variance in subject age, biopsy site and extent, histologic or histochemical technique, and perhaps the degree of inflammation present at the time of biopsy. Careful immunohistochemical and in situ molecular assays on well-defined loci within the conjunctiva of comparable human subjects may resolve such questions in the future. Organized mucosa-associated lymphoid tissue is rigorously defined as mucosal lymphoid follicles with an ultrastructurally distinct overlying lymphoepithelium. Based on available evidence, the epithelium overlying mammalian conjunctival lymphoid follicles does not contain distinct M cells. Whether zonal differences in morphology reflect real differences in the capacity to sample tear film antigens for presentation to the mucosal immune system remains to be established.

E-cadherin distribution and epithelial basement membrane characteristics of the normal human conjunctiva and cornea

The conjunctival mucosa has several similarities to the mucosal immune system of the gut and bronchus. Like the gut and bronchial mucosa, the conjunctiva is capable of inducing tolerance to encountered antigens and possesses a repertoire of CD8+ intraepithelial lymphocytes (IELs) bearing the human mucosal lymphocyte-1 antigen (HML-1) which has been shown to be an alpha E beta 7 integrin. The epithelial cells surface ligand for HML-1 is E-cadherin. The distribution of E-cadherin in the normal human conjunctiva and cornea is not known. We investigated E-cadherin distribution in the conjunctiva and cornea by immunohistochemistry. E-cadherin was found to be present in all layers of the conjunctival epithelium but not in corneal epithelium. In the conjunctiva it may act as a ligand for the HML-1+ IELs. The specific location of IELs along the basal cells of the conjunctiva compared with the generalised distribution of E-cadherin through all layers, indicates that factors other than E-cadherin binding determine the distribution of HML-1+ IELs. We performed electron microscopy on de-epithelialised conjunctival and corneal samples. We demonstrated the presence of epithelial basement membrane pores in the conjunctiva but not in the cornea. Lymphocyte migration from the substantia propria to the intraepithelial compartment appears to occur through these pores, which may also serve as a conduit for antigen presentation by epithelial antigen presenting cells (APCs) to lymphocytes in the substantia propria.

Mucosal defense of the outer eye

A combination of mechanical, anatomical, immunological, and microbiological factors prevent infection of the outer eye. Mechanical and anatomical factors include the intact epithelium of the conjunctiva and cornea and the constant blinking action of the eyelids. Tear components that play a role in eye defense include lysozyme, immunoglobulins, lactoferrin, and betalysin. The normal bacterial flora of the conjunctiva may also have an inhibitory effect on the survival of more pathogenic species. The eye is linked to the common mucosal immune system, thus gaining the benefits of a system of microbial defense which is primed in the gastrointestinal tract, where a continuing large antigen load is capable of stimulating ongoing immune protection. The relative roles of the various factors contributing to prevention of eye infection remain to be fully defined.

Phenotypic analysis of resident lymphoid cells in the conjunctiva and adnexal tissues of rat

The conjunctival associated lymphoid tissue is considered to be an integral part of the mucosal immune system. Under normal circumstances immune mechanisms in mucosal associated lymphoid tissue of the gut and bronchus can selectively suppress, rather than enhance, immune responsiveness to encountered antigens, inducing a state of tolerance. It is possible that conjunctival associated lymphoid tissue can also induce a state of tolerance to encountered antigens. Such a response may be exploited to modulate immune mediated ocular disease. Enhanced tolerance may protect the host against foreign antigen. Alternatively, under certain circumstances when the normal immune system is altered or disrupted the mucosal tissue may act to induce sensitisation and trigger immune mediated disease. The rat is frequently used as an animal model of immune mediated eye disease, but the normal profile of immune cells in the rat conjunctiva has not been studied. This information is essential for meaningful interpretation in the experimental situation. In this study we examined the immunophenotype of lymphoid tissue associated with the conjunctiva, lacrimal gland and Harderian gland of the Lewis rat. CD4+, Ia+ and the monocyte/macrophage population of cells were found predominantly in the substantia propria of the conjuctiva and interstitial connective tissue of the glands. CD8+ cells were distributed mainly in relation to the conjunctival and glandular epithelium. Goblet cells stained strongly with the monoclonal antibody (MAb) MRC OX-39, which is a marker for IL-2 receptors. The overall pattern of distribution of immunocompetent cells in the rat was found to be similar to that reported in humans.

Characterisation of the normal conjunctival leukocyte population

Lymphoid cells are present in normal mucosal tissue as scattered cells or organised into MALT. Knowledge of the non-pathological conjunctival lymphoid tissue is a vital basis for the further study of ocular surface inflammatory disorders. Therefore, we used immunohistochemistry to examine the leukocyte population of tarsal and bulbar conjunctiva from normal patients with no ocular or systemic inflammatory disease. CD3+ T cells were the most frequently occurring, and macrophages the second most frequently occurring, conjunctival cell type and were seen in the epithelium and substantia propria. There were greater numbers of leukocytes in the bulbar than in the tarsal area and this reached statistical significance for CD3+ T cells and CD57+ NK cells. In both bulbar and tarsal conjunctiva, B cells and neutrophils were seen in the epithelium and substantia propria, but plasma cells, NK cells and mast cells were present only in the substantia propria. No eosinophils were seen. CD8+ cells outnumbered CD4+ cells in the epithelium (CD4:CD8 0.3) but this was reversed in the substantia propria (CD4:CD8.1.3 tarsal, 2.0 bulbar). Most epithelial T cells and half the stromal T cells were CD45Ro+. IL-2R (CD25) staining was infrequent in the tarsal but not the bulbar area. The greater number and activation of T cells in the bulbar region may relate to greater antigen exposure. HLA-DR+ cells were mainly macrophages, but also included dendritic cells in the epithelium and a few epithelial cells. The conjunctival lymphocytes do have certain features of MALT cells, apart from mucosal recirculation, homing and promotion of sIgA production. Conjunctival IEL, like gut IEL, are predominantly CD8+, are found in the basal epithelium, are HML-1+, and have very high expression of CD45Ro. Substantia propria lymphocytes have more equal CD4 and CD8 numbers and frequently express CD45Ro. We found only one example of organised conjunctival lymphoid tissue in our study and suggest that the presence of CALT in humans is not universal.