Sensory innervation of conjunctival lymph follicles in cynomolgus monkeys

The importance of neuroregulation of immunoresponsiveness is recognized, but little is known of the innervation of conjunctival follicles. The access and distribution of nerves in follicles of the palpebral conjunctiva were therefore studied and those of trigeminal nerve origin distinguished.

Serial sections of follicles were prepared for light and selected sections for electron microscopy. Intracranial lesions were made in ophthalmic or both ophthalmic and maxillary nerves several days before fixation in three of the six monkeys used and their distribution in follicles identified by induced degeneration.

Fine nerves penetrated follicles and terminated on arterioles, smaller blood vessels, and rarely on high endothelial venules. Other nerve branches entered the follicle parenchyma, conducted, and terminating in fine reticular fibers. Many terminals were identified as autonomic on morphologic grounds. Few terminals were in direct contact with lymphocytes and none were found in germinal centers. Other fibers terminated in the follicle associated epithelium. A large fraction of the nerve displayed degenerative changes after lesions and epithelial terminals were no longer present.

Nerve distribution is mostly similar to that found in other lymphoid organs with the exception of the epithelial terminals, which are described for the first time in mucosa-associated lymphoid tissue and identified as sensory. Because epithelial terminals virtually were absent from the surrounding unspecialized epithelium, it is likely that those of the follicular epithelium have a specific immune system-related function. They may represent a follicle-alerting mechanism to surface stimuli.