Liver as a tumor cell killing organ: Kupffer cells and natural killers.

Sinusoidal rat liver cells spontaneously kill tumor cells in vitro. They have the same preferences as do spleen cells for certain types of tumor cells, YAC-1, P815, BSP73Asml, BSP73As, EB, EsB, and L5222. Metastasizing tumor cells are less sensitive than their nonmetastasizing counterparts. Not all effector cells are Kupffer cells. These nonmacrophage killer cells share some features with classical natural killers: (a) fast reactions (4 h); (b) high toxicity against YAC-1 cells; (c) sensitivity to anti-asialo GM1 globulin; (d) similar age dependency; (e) short biological halflife (approximately 1 day) (deduced from radiation experiments); (b) silica particle insensitivity; and (g) nonadherence. The natural killing potency of the liver is higher than that of the spleen. The reduction of tumoricidal capacity of the liver in germ-free animals suggests environmental influences. Tumoricidal capacity (organ capacity) is increased in rats chronically fed thioacetamide, carbon tetrachloride (CC14), dimethylaminoazobenzene, and N-nitrosomorpholin.