The role of Kupffer cells in the differentiation process of hepatic natural killer cells.

Pit cells, or hepatic natural killer (NK) cells, present in rat liver sinusoids, represent an organ-associated NK cell population, with a higher level of activation and a different morphology when compared with peripheral blood NK cells. These cells are the result of an influx of peripheral blood NK cells in the liver microenvironment, followed by an activation or differentiation process toward the highly activated phenotype. In this work we investigated the role of Kupffer cells in this differentiation process of NK cells in the liver sinusoids. In vivo elimination of Kupffer cells with the macrophage cytotoxic drug dichloromethylene diphosphonate induced a decrease in number of hepatic NK cells that paralleled that of Kupffer cells. This effect was further investigated in vitro. Kupffer cell-conditioned medium appeared to enhance the viability, tumor-cytotoxic activity, and adherence of hepatic NK cells to liver endothelial cells in vitro. We conclude therefore that Kupffer cells, present in the microenvironment of the liver sinusoids, play an essential role in the differentiation process of peripheral blood NK cells to the highly activated hepatic NK cell population.