Arrangement of the small intestine lymphatic network in the Peyer's patches of the mouse. A light and transmission electron microscopic study.

The lymphatic network in Peyer's patches has been previously studied by scanning electron microscopy in rabbit and sheep. So far, data on the Peyer's patch lymphatic network obtained by light and transmission electron microscopy are still lacking. The present work was carried out on several series of consecutive thick and semithin sections of mouse Peyer's patches. Ultrastructural analyses were performed on ultrathin sections by traditional transmission electron microscopy. Lymph vessels were detected in the parafollicular and subfollicular areas of Peyer's patches. Two independent lymphatic plexuses, the muscularis mucosae lymphatic plexus and the subfollicular plexus, were identified respectively in the mucosal and submucosal layers. These lymphatic plexuses joined outside the patch, both draining into the submucosal lymphatic network of the small intestine. At the ultrastructural level, the muscularis mucosae lymphatic plexus, and the lymph vessels draining into it, showed a close association with bundles of smooth muscle cells. Numerous nerve fibres were detected in proximity to the lymphatic endothelium and, in some cases, synapse-like neuroendothelial associations were observed. We report here the lymph vessel organization observed in mouse Peyer's patches and discuss the meaning of the presence of subendothelial nerve terminals.