The predominant role of the spleen in lymphocyte recirculation. I. Homing of lymphocytes to and release from the isolated perfused pig spleen.

Lymphocyte recirculation through the isolated pig spleen was studied by means of a perfusion system which kept the organ alive for a prolonged period of time. By changing the perfusate to a leucocyte-enriched or cell-free perfusate and taking serial arterial and venous samples, the numbers of lymphocytes which homed to or were released from the spleen were measured. In all experiments more lymphocytes homed than were released per minute. There was no apparent difference when autologous or allogeneic cells were used. The number of lymphocytes released depended on the number of lymphocytes homed previously. During the phase of constant release up to 3-3 X 10(6) lymphocytes were released per gram spleen per minute. From these values it can be extrapolated that up to 270 X 19(9) lymphocytes recirculate through the isolated pig spleen per day. Based on kinetic data from other species it is estimated that in the entire pig a total number of 300-400 X 10(9) lymphocytes recirculate per day. Thus, it can be concluded that the spleen is the most important organ for lymphocyte recirculation in the pig.