Cellular and humoral dynamics in the periarterial lymphatic sheaths of rat spleens

Humoral and cellular dynamics in the periarterial lymphatic sheath (PALS) of the splenic white pulp were investigated in regards to the lymph flow and the architecture of the deep lymphatics in rat spleens. The effects of the splenic venous pressure on the lymph flow were also examined. We found a remarkable depletion of lymphocytes in the PALS and strong lymph flow to the deep lymphatics from the red pulp when the spleen was perfused via the splenic artery at a high speed with a high venous pressure. It was evident that lymphocyte depletion in the PALS depended on the venous pressure during the perfusion. Hemorrhage and lymphocyte depletion in the PALS also occurred after the ligature of the splenic vein. The migration of charcoal particles into the PALS via the red pulp was observed after intravenous or direct injection of charcoal particles. However, the bridging channels in the marginal zone (MZ) were always free of charcoal particles. The existence of deep lymphatics was confirmed around the central arteries which were more than 20 microns in diameter. The ligature of the thoracic duct resulted in the dilatation of the deep lymphatics and intercellular spaces which were easily recognized as the termination of the splenic lymphatics. The terminal lymphatics were localized only in the PALS but not in the follicles. Therefore, the PALS might be considered to act as a central station of the extra-vascular pathway which is connected to both the deep lymphatics and the MZ bridging channels.