Two kinds of NK cell are found in the liver. Liver-resident NK cells are found only in the liver, not in the blood. They are likely to have a special role in the liver, but we do not yet know what this is. Recirculating NK cells are blood NK cells that enter the liver and then leave again. Liver-resident NK cells produce large quantities of two immune messengers called IFNγ and TNFα, which are known to be important factors for the progression of NAFLD to NASH. Recirculating NK cells also produce IFNγ but, unlike liver-resident NK cells, they tend to kill other cells. This could be harmful in NAFLD, for example if they kill the functional cells of the liver, hepatocytes. On the other hand, they could be helpful, for example by killing hepatic stellate cells, which are the cells that cause scarring and cirrhosis. Our group aims to find out what liver-resident NK cells do in the healthy liver, and how both liver-resident and recirculating NK cells may be involved in NAFLD and NASH.