The effect of topical cyclosporin on conjunctiva-associated lymphoid tissue (CALT)

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.

The Conjunctiva-Associated Lymphoid Tissue in Chronic Ocular Surface Diseases

Ocular surface diseases (OSDs) represent a widely investigated field of research given their growing incidence and the negative impact on quality of life. During OSDs, cytokines generated by damaged epithelia trigger and deregulate the lymphoid cells composing the eye-associated lymphoid tissues, inducing an immune-mediated chronic inflammation that amplifies and propagates the disease during time. The conjunctiva-associated lymphoid tissue (CALT), given its particular position that permits immune cells covering the cornea, might play a crucial role in the development of OSDs. Despite the recognized inflammatory role of mucosa-associated lymphoid tissues in other stations taking contact with the external environment (gut or bronchus), CALT did not gain the deserved consideration. In the last years, the diffusion of the in vivo confocal microscopy (IVCM) stimulated the interest to CALT, especially in dry eye, ocular allergy, and glaucoma. Though the initial stimuli were different, IVCM documented similar changes, represented by increased lymphoid cells within the diffuse layer, follicles and interfollicular spaces. These findings, which need to be validated by immunohistology, support the CALT stimulation during OSDs. However, while an involvement of the CALT in OSDs is hypothesizable, the exact role of this structure in their pathogenesis remains unclear and warrants further investigations.

Characterization of membranous (M) cells in normal feline conjunctiva-associated lymphoid tissue (CALT)

OBJECTIVE

To characterize conjunctival lymphoid nodules obtained from the nictitans of healthy cats to determine if the follicle-associated epithelium (FAE) of conjunctiva-associated lymphoid tissue (CALT) in this species contains membranous (M)-cells analogous to those described in other regions of mucosa-associated lymphoid tissue (MALT).

METHODS

Lymphoid follicles from nictitan bulbar surfaces of 10 healthy cats (20 eyes total) were examined. Nictitans from five cats were harvested immediately post-mortem and a minimum of 12 lymphoid nodules from each third eyelid were isolated using a Zeiss operating microscope. At least three lymphoid follicles from each eye were examined using light microscopy (LM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) using standard fixation and embedding protocols. Nictitan-lymphoid follicles from another five healthy cats were processed for immunohistochemistry to characterize the distribution of T- and B-lymphocytes present beneath the FAE.

RESULTS

The FAE overlying CALT from 10 healthy cats demonstrated morphology characteristic of M-cells including attenuated apical cell surface with blunted microvilli and microfolds, invaginated basolateral membrane forming a cytoplasmic pocket, and diminished distance between the apical and pocket membrane. Immunohistochemistry of lymphoid tissue subtending the FAE demonstrated B-cell dependent regions in the germinal centers surrounded by T-cell dependent interfollicular zones.

CONCLUSIONS

Healthy feline CALT contains morphologic features analogous to those described in other regions of MALT. Documentation of feline conjunctival M-cells is of clinical relevance in the study of primary infectious, allergic, and autoimmune ocular diseases, as well as a potential means of vaccination or drug delivery.

Ocular drug delivery - a look towards nanobioadhesives

IMPORTANCE OF THE FIELD

A major challenge emanating in the design of topical ophthalmic preparations is their short precorneal residence time. Retention of a drug delivery system in the front of the eye is thus desirable. One solution identified to address this concern is a retentive system that can preferably be delivered in a liquid drop form and ultimately remain attached to the corneal tissue owing to incorporation of a bioadhesive component. Forward-thinking approaches are required to achieve advancements in this approach for the attainment of an effective drug concentration at the site of action. Accordingly, several investigators have identified the benefits of nanotechnology-based drug delivery systems for ophthalmic drug delivery.

AREAS COVERED IN THIS REVIEW

A concerted effort was made to review critically all 'nanobioadhesives', that is, nanosystems designed for ocular drug delivery with the goal of attaining prolonged ocular retention, in a systematic, chronological manner, from their reported point of inception to the present.

WHAT THE READER WILL GAIN

A perspective on possible future trends in this growing field of ocular drug delivery is formulated.

TAKE HOME MESSAGE

The importance of and need for new developments in the field of ocular nanobioadhesives is emphasized.

Ocular defense mechanisms with special reference to the demonstration and functional morphology of the conjunctiva-associated lymphoid tissue in Japanese monkeys

In order to define the histological components of ocular defense, the conjunctiva in Japanese monkeys was studied using a whole mount method, light microscopy, and electron microscopy. We investigated the distribution of the conjunctiva-associated lymphoid tissue (CALT) using stereoscopic observations of the conjunctiva immunostained with human leukocyte antigen (HLA)-DR antibody and /or stained with alcian-blue. The outer surface of the conjunctival fornix was lined by sheets of mucus secreting goblet cells, with small epithelial patches without goblet cells, scattered among them. The patches, termed CALT, consisted of flattened epithelial cells, intraepithelial lymphocytes and dendritic cells, and lymphoid follicles with a germinal center. The CALT in Japanese monkeys was fundamentally similar in structure to those found in other animal species. CALT patches ranged in size ranging from 200 microm to 300 microm in diameter. The number of patches varied from 20 to 40 in the superior eyelid and 10 to 20 in the inferior eyelid. Latex microspheres administrated as eye drops were selectively taken up first by flattened associated epithelial cells covering the surfaces of CALT patches and then by intraepithelial dendritic cells of the CALT. These morphological findings show that CALT patches in the eyelids of primates are focal sites for particulate uptake and contact with lymphoid constituents, indicating that they are inductive sites for the common mucosal immune system as well as important components in ocular defense.

Efficacy of Systemic Cyclosporine A and Amniotic Membrane on Rabbit Conjunctival Limbal Allograft Rejection

PURPOSE

To evaluate the effect of intramuscular cyclosporine A (CsA) and amniotic membrane (AM) on conjunctival limbal allograft survival in a rabbit model.

METHODS

Eighty-two female rabbits (59 New Zealand white rabbits, 23 Dutch pigmented rabbits) were used. The New Zealand white rabbits were divided into 4 treatment groups: group 1 (n=13), conjunctival limbal autograft transplantation; group 2 (n=12), conjunctival limbal allograft transplantation without additional treatment; group 3 (n=18), conjunctival limbal allograft transplantation and human AM; and group 4 (n=16), conjunctival limbal allograft transplantation and systemic CsA (10 mg/kg/day intramuscularly). The 23 Dutch pigmented rabbits were used as limbal stem cell allograft donors. The rejection index, the mean survival time, and the rejection rates were calculated for each group.

RESULTS

After 28 days of follow-up, there were no episodes of limbal rejection in groups 1 and 4, whereas the rejection rate was 100% in groups 2 and 3. There was no significant difference in mean survival time of the rejected grafts between groups 2 and 3.

CONCLUSIONS

A model of rejection of conjunctival limbal transplantation was developed in the rabbit. Intramuscularly injected CsA effectively prevents limbal allograft rejection. Human AM is not useful for this purpose.

Chitosan nanoparticles: a new vehicle for the improvement of the delivery of drugs to the ocular surface. Application to cyclosporin A

Present limitations in the management of extraocular diseases include the inability to provide long-term extraocular drug delivery without compromising intraocular structures and/or systemic drug exposure. In the present study, the potential of chitosan (CS) nanoparticles as a new vehicle for the improvement of the delivery of drugs to the ocular mucosa was investigated. Cyclosporin A (CyA) was chosen as a model compound because of its potential usefulness for the treatment of these local diseases. An ionic gelation technique was conveniently modified in order to produce CyA-loaded CS nanoparticles. These nanoparticles had a mean size of 293 nm, a zeta potential of +37 mV and high CyA association efficiency and loading (73 and 9%, respectively). In vitro release studies, performed under sink conditions, revealed a fast release during the first hour followed by a more gradual drug release during a 24-h period. In vivo experiments showed that, following topical instillation of CyA-loaded CS nanoparticles to rabbits, it was possible to achieve therapeutic concentrations in external ocular tissues (i.e., cornea and conjunctiva) during at least 48 h while maintaining negligible or undetectable CyA levels in inner ocular structures (i.e., iris/ciliary body and aqueous humour), blood and plasma. These levels were significantly higher than those obtained following instillation of a CS solution containing CyA and an aqueous CyA suspension. From these results, we can conclude that CS nanoparticles may represent an interesting vehicle in order to enhance the therapeutic index of clinically challenging drugs with potential application at extraocular level.

Successful treatment of dry eye in two patients with chronic graft-versus-host disease with systemic administration of FK506 and corticosteroids

PURPOSE

We present two cases of severe dry eye in patients with chronic graft-versus-host disease (CGVHD) after hematopoietic stem cell transplantation (SCT) who were successfully treated by the systemic administration of FK506 and corticosteroids.

METHODS AND RESULTS

A 29-year-old man with chronic myelogenous leukemia underwent SCT. Oral and lung CGVHD developed on approximately day 130, and dry eye associated with CGVHD was diagnosed on day 168. The patient began receiving cyclosporin A (150 mg/d) for the treatment of oral and lung CGVHD. Treatment with prednisolone (1 mg/kg/d) began on approximately day 300. Oral and lung GVHD improved slightly, but worsened again although systemic administration of cyclosporin A and prednisolone were continued. Cyclosporin A was discontinued, and systemic administration of FK506 was started on day 376. Forty-four days later, marked improvement in the ocular surface and other organs was observed. However, the dry eye worsened while tapering FK506, with no flare of other affected organs. A 43-year-old woman with myelodysplastic syndrome underwent SCT. She received FK506 for prophylaxis of CGVHD. She had mild dry eye before SCT. Oral and intestinal CGVHD developed, and the dry eye worsened significantly on approximately day 150 while tapering FK506. Treatment with prednisolone (1 mg/kg/d) began, and the dose of FK506 was increased. By day 240, the symptoms of dry eye and the findings of the ocular surface markedly improved, and CGVHD in other organs was completely resolved. However, the improvement in the dry eye was lost when FK506 was tapered for the second time.

CONCLUSION

Systemic administration of FK506 with corticosteroids is an effective treatment of severe dry eye in patients with CGVHD, but long-term administration may be required to achieve a lasting response. These cases also suggest that further investigation into the use of topical FK506 and prednisolone as a maintenance therapy should be pursued.

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.

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.

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.