Abstract
Purpose:
In the human ocular surface, the conjunctiva, lacrimal gland and lacrimal drainage system have an Eye-Associated Lymphoid Tissue (EALT). As part of the mucosal immune system it maintains immunological homeostasis and modulates inflammatory ocular surface disease. Rat and mouse however, which are common animal models for ocular inflammatory mechanisms, lack EALT but instead have NALT. It is discussed whether this may functionally replace EALT in these animal models.
Methods:
NALT was obtained from 10 normal young adult DA and Lewis rats, as well as of BL/6 Mice according to the ARVO Statement for the Use of Animals in Ophthalmic and Visual Research regulations. Tissues were photo-documented, embedded, sectioned & stained for histology and compared to human tissues.
Results:
EALT in man consists of diffuse lymphoid tissue from the lacrimal gland throughout the conjunctiva (as CALT) and along the lacrimal drainage system (as LDALT). Lymphoid follicles with antigen-transporting M-cells, germinal centers and T-cell zones in CALT and LDALT can serve for antigen uptake and effector cell production. Rats and Mice have a large NALT arranged in two voluminous tissue strands on the bottom of the two nasal cavities, left and right, separated from the oral cavity by the hard palate and connected to the eye by the lacrimal drainage system. It consists of diffuse lymphoid tissue along the respiratory epithelial part and of a strand of central follicles covered by a typical FAE without goblet cells.
Conclusions:
The central and the mucosal immune system have different functions and favour inflammation or tolerant immune reactions, respectively. Although end stages of ocular inflammation in rat and mouse may resemble certain aspects of human disease, they can probably not reflect the fine tuning of immunity that occurs in human EALT prior to disease outbreak. Investigation of NALT may be a useful tool for inflammatory research in rat and mouse.<br /> Grant support: DFG KN317/11<br /> Financial interest: None