Characterization of a major natural killer activity in rat lungs

A high level of antitumoral cytotoxicity was observed in the lymphoid population extracted by perfusion from lung capillaries. The in vitro cytotoxicity against tumor cells was demonstrated with the murine lymphoma YAC-1 cells or with the syngeneic P 77 rat lung fibrohistiocytoma cells. It was demonstrated that this cytotoxic activity had the characteristics of natural killer activity. At the same effector to target ratio the efficiency of this population was higher than in blood or spleen. Since the total number of lymphoid cells arrested in the capillary of the lungs is very high the lungs seemed an immunologically privileged site. A close relationship was observed between this activity in vitro and the rapid elimination in vivo of same tumor cells trapped in lungs (more than 99% after 24 hours).