Organization of the lymphatic vessels and their relationships to blood vessels in rabbit Peyer's patches.

The three-dimensional organization of the lymphatic vessels and their relationship to blood vessels in rabbit Peyer's patches were demonstrated by scanning electron microscopy (SEM) of corrosion casts and of tissues. The interconnected central lacteals in the villi overlying the interfollicular area were connected with the lymphatic plexus in the area. There were many blind-ending lymphatic vessels in the upper part of the interfollicular area. These lymphatics gradually fused and formed perifollicular lymphatic sinuses which surrounded the lateral surfaces and bottoms of the follicles. There were no lymphatic vessels within the dome and the follicle. The perifollicular lymphatic network surrounded the capillary network of the follicle. Between the perifollicular lymphatic networks in the interfollicular area were many high endothelial venules (HEVs) which collected the capillaries in the dome and the follicle. The voluminous perifollicular lymphatic sinuses seemed to have a great potential capacity as both reservoirs and as drainage routes for fluid and lymphocytes. The close association of HEVs with the perifollicular lymphatic vessels seemed to facilitate the prompt drainage of fluid and macromolecules leaking out of HEVs during lymphocyte migration into the lymphatics. That the HEVs are downstream of the capillaries in both the dome and the follicle suggests that substances such as cytokines may be involved in the induction of the post capillary venules into HEVs.