Classification of lymphocytes recirculating in the spleen.

After washing out remaining blood cells using cold perfusate, pig spleens were connected to a closed-circuit normothermic perfusion system. Recirculating lymphocytes migrated out and rapidly established an equilibrium with the splenic extravascular lymphoid tissues. Comparison of the subpopulations among these lymphocytes with those in the blood at time of removal of the spleen, showed the absence of Null cells and reduced numbers of weakly E-rosetting cells among splenic emigrants. The proportion of other B- and T-cell subpopulations were increased in a way which might be explained by non-recirculation of these two subpopulations. Autologous blood lymphocytes labelled with fluorescein isothiocyanate and introduced into spleen perfusions rapidly established equilibrium (approximately 15%-25%, well within 1 hr) and at the end of perfusion were concentrated in the marginal zones. The fluorescent lymphocytes remaining in the perfusate showed a marked enrichment of Null cells suggesting that these cells do not home to splenic extravascular lymphoid tissues in agreement with the hypothesis that Null cells are absent from splenic emigrants because they are nonrecirculating cells.