ABSTRACT
The epithelia of the ocular surface, the corneal and conjunctival epithelia, as well as the epithelium of the efferent tear ducts, together with the meibomian glands and main and accessory lacrimal glands and lids, comprise a physiological system that was recently summarized under the term lacrimal-ocular surface system (LOS) (1). The LOS is organized to maintain the clarity of the cornea-a homeostatic set-point. Like the systems that represent epithelial interfaces between the internal and external environments, i.e. the gastrointestinal, integumentary, and respiratory systems, the LOS collaborates with the innate and adaptive immune system to respond to microbial invasion. One venue of this collaboration is comprised of the lacrimal glands, conjunctiva, and efferent tear ducts, which are
populated by IgA-producing plasma cells and whose epithelia actively transport secretory IgA into the nascent tear fluid (Fig. 1) (2).
