Lymph pathways associated with three types of follicle structure found in gut-associated lymphoid tissue of horse ileum.

In the horse ileum, lacteals in the villi are continuous with prelymphatic intercellular channels and a plexus of lymphatic sinuses in the lamina propria that encircle the domes of the follicle/dome structures and proprial follicles. These sinuses may act as the major entry site for many of the lymphocytes migrating from gut-associated lymphoid tissue via the lymphatic system. Vessels from this plexus penetrate the muscularis mucosae and lymph flows into lymphatic vessels within the interfollicular tissue between the follicles of both follicle/dome structures and lymphoglandular complexes (LGCs). No lymphatic vessels leave the follicles, but intercellular pathways of the follicles are continuous with those in the surrounding interfollicular tissue and follicular sinuses around the base of the follicles. These pathways appear to provide the only available lymphatic route for lymphocytes leaving LGCs to enter the lymphatic system. Lymph from the interfollicular tissue enters deep submucosal lymphatic vessels, containing prominent valves, which drain into other vessels transporting lymph from the surface of the ileum.