Ileal Peyer's patches in pigs: intercellular and lymphatic pathways

The lymphatics of Peyer's patches disseminate immunological information from the gut and thus play a key role in protection of the body against environmental pathogens. The aim of this project was to describe the lymphatic pathways of these Peyer's patches in pigs, and the mucosal intercellular spaces which lead to these lymphatics.

Ileal tissue from living or freshly killed pigs was examined by light microscopy or electron microscopy, or was injected with Mercox (CL-2B, Japan Vilene Hospital, Tokyo) for scanning electron microscopy of corrosion casts.

Intercellular fluid between intestinal epithelial cells passes through pores in the basal lamina to mix with that in the intercellular spaces and prelymphatic intercellular channels of the lamina propria and follicle domes. From there, lymph enters lacteals in the villi, or a branching network of vessels within the lamina propria. Small lymphatics penetrate the muscularis mucosae and are continuous with (1) lymphatic vessels which pass directly to the deep submucosa between follicles, or (2) lymphatic sinuses which lie adjacent to the follicles. This differs from the situation in sheep and rabbits. Basal lymphatics beneath the follicles convey lymph to vessels which leave the surface at the serosa.

The differences in the structure and arrangement of the lymphatics of Peyer's patches between pigs, sheep, and rabbits will require further investigation to determine if such variation between species has an effect on the distribution of immune products to effector sites.