Abstract
Purpose::
The normal ocular surface is protected by components of the mucosal immune system termed Eye-associated lymphoid tissue (EALT) as described in the human. This consists, following the tear flow, of the lacrimal gland associated lymphoid cells, the conjunctiva-associated lymphoid tissue (CALT) and of the lacrimal drainage associated lymphoid tissue (LDALT). Its occurrence, morphology and topography in the rabbit was investigated in the present study.
Methods::
Whole-mount tissues of the conjunctiva, lacrimal drainage system and lacrimal glands (LG) from 28 young adult rabbits were investigated native in reflected light, in histology, confocal microscopy, scanning (SEM) and transmission electron microscopy (TEM).
Results::
A diffuse lymphoid tissue was continuous from the lacrimal gland along the conjunctiva into the lacrimal drainage system and showed local production of IgA and its transporter SC in all tissues. Lymphoid follicles occurred in the conjunctiva and lacrimal drainage system associated with high endothelial venules (HEV) for regulated lymphocyte immigration. Lymphoblasts, follicular dendritic cells, apoptotic cells and macrophages formed bright germinal centers (GC). The specialized follicle-associated epithelium (FAE) without goblet cells contained groups of lymphoid cells, frequently positive for MHC-class II, located inside cytoplasmic pockets of superficial electron lucent cells. The latter contained sparse cytokeratin bundles and numerous endocytotic vesicles, expressed Vimentin and showed uptake of FITC coated Latex microspheres; the underlying basement membrane was discontinuous from lymphocyte transmigration.
Conclusions::
The rabbit ocular surface hence has an anatomy with an eye-associated mucosal immune system (EALT) similar to the human, which can maintain the afferent and efferent arms of mucosal immunity. It may therefore be a more promising animal model for future experimental studies of ocular surface immune reactions than the frequently used mouse or rat.
Keywords: conjunctiva • immunomodulation/immunoregulation • microscopy: light/fluorescence/immunohistochemistry