THE KINETICS OF LYMPHOCYTE RECIRCULATION WITHIN THE RAT SPLEEN

The migration of lymphocytes from the blood into the splenic pulp and the release of lymphocytes from the spleen into the blood was studied by isolating the rat spleen and perfusing it with 15 ml of recirculating, oxygenated blood. When thoracic duct lymphocytes labelled with tritiated uridine were added to the initial perfusate the concentration of these cells fell exponentially for 2–3 hr and then rose to a flat secondary peak. From this pattern it was inferred that small lymphocytes entered the spleen at a rate proportional to their instantaneous concentration in the perfusate, traversed the splenic pulp and re-entered the perfusate with a minimum transit time of 2–3 hr. The rate of release of small lymphocytes from the spleen was not influenced by the prevailing concentration of small lymphocytes in the perfusate but probably reflected the rate of migration into the spleen over a period earlier than 2 hr before. The rate of exchange of small lymphocytes between the blood and the intact spleen in vivo was estimated to be about 84 × 10⁶ cells/hr. The size of the intrasplenic pool of recirculating small lymphocytes was probably 400–500 × 10⁶ cells. The rate of migration of small lymphocytes into the spleen was not affected by prior irradiation of the spleen donor. When either of two antigenic materials were added to the perfusate no inhibition of lymphocyte migration into the spleen was noted although the release of lymphocytes from the spleen was diminished by the addition of a large dose of sheep erythrocytes.