Regulation of the inflammatory component in chronic dry eye disease by the eye-associated lymphoid tissue (EALT).

PURPOSE

The physiologically protective mucosal immune system of the ocular surface consists of lymphocytes, accessory leukocytes and soluble immune modulators. Their involvement has also been observed in inflammatory ocular surface diseases, including dry eye syndrome, and we have attempted here to describe their interaction.

METHODS

Our own results regarding the mucosal immune system of the human ocular surface are discussed together with the available literature on mucosal immunity and inflammatory ocular surface disease.

RESULTS

The mucosa of the ocular surface proper (conjunctiva and cornea) is anatomically continuous with its mucosal adnexa (the lacrimal gland and lacrimal drainage system) and contains a mucosal immune system termed 'eye-associated lymphoid tissue' (EALT). This extends from the periacinar lacrimal-gland-associated lymphoid tissue along the excretory ducts into the conjunctiva-associated lymphoid tissue (CALT) and further into the lacrimal drainage-associated lymphoid tissue (LDALT). EALT consists of continuous diffuse lymphoid effector tissue and of interspersed follicles for effector cell generation in CALT and LDALT. Typical events in ocular surface disease include alteration and activation of epithelial cells with loss of epithelial integrity, production of inflammatory cytokines, and potential presentation of non-pathogenic and self-antigens - leading to a loss of immune tolerance. Events in the deregulation of physiologically protective EALT, resulting vicious circles, and eventual self-propagating immunomodulated inflammatory disease processes are explained, discussed and visualized by schematic drawings.

CONCLUSION

Deregulation of EALT can orchestrate a self-propagating inflammatory mucosal disease process if the capacity of natural compensatory factors is overridden and if the disease is not limited by timely diagnosis and therapy.