Natural killer lymphocytes in rat liver sinusoidal blood

Blood-borne cells with the characteristics described for the natural killer (NK) lymphocytes were recovered from the liver sinusoids in rat. They had cytotoxic activity against K 562 cells in a 18 h 51Cr release assay, target binding rate and large granular lymphocytes percentage higher than the inflowing portal blood cells. The cytotoxic effector population was non-adherent and peroxidase negative, enriched in cells with Fc- and C36-receptors. Deprivation of liver of portal or mesenteric blood supply significantly decreased the liver NK activity not affecting the level of cytotoxicity in the portal blood. Splenectomy produced only a moderate decrease of activity. These findings may indicate that liver sinusoids is the site of accumulation of blood-born NK cells or of maturation of the NK-precursors. One possible mechanism by which natural cytotoxicity controls tumor growth and spread might be the killing of circulating tumor cells arrested in the liver by the blood-born NK-cells.