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

Abstract

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 μm to 300 μm 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.