Kupffer cells decrease metastasis of colon cancer cells to the liver in the early stage.

Although Kupffer cells (KCs) play an important role in the liver's immune response, their role in colon cancer metastasis to the liver is unclear. We here analyzed the relationship between KCs and tumor cells (TCs) in colon cancer metastasis to the liver. Fischer 344 (F344) rats were divided into control group (KC+ group) and KC elimination group (KC‑ group), in which KC elimination was induced by Cl2MDP liposome injection. RCN‑H4 colon cancer cells were injected into the rats of both groups, and the relationship between the two types of cells was observed by intravital microscopy (IVM) for 6 h. Moreover, to investigate the effect of KCs on liver metastasis formation, KCs were eliminated at different time points before and after the TC injection. The number of metastatic nodules 2 weeks after the injection was evaluated. In the KC‑ group, IVM revealed that the number of adherent TCs had increased 1.5‑fold at 6 h after the TC injection as compared with in the KC+ group. Moreover, in the KC+ group, 74% of the TCs adhered to the KCs, and KC activation and KC phagocytosis of the TCs were observed. Two weeks after the injection, the number of metastatic nodules was significantly increased in rats in which the KCs had been eliminated before the injection, but not in rats in which the KCs had been eliminated after the injection. KC activation and KC phagocytosis of TCs decreased colon cancer cell metastasis to the liver.