Obesity-associated diseases are increasing in prevalence in the western world. Accumulation of excess lipid in the liver often results in the development of steatosis which typically progresses to the more severe liver disease known as non-alcoholic steatohepatitis (NASH). Liver resident macrophages, called Kupffer cells (KCs), have been implicated in the progression of NASH, although the exact role they play is currently unclear. We have found that KCs have the necessary machinery to aid in lipid processing in the liver and hypothesize that they perform this function on a daily basis. Macrophages are however also highly susceptible to lipid induced toxicity, thus KCs may not be able to cope with the excess of lipids present in a Western diet, potentially leading to the development of NASH. In this project we propose to study the role of KCs in lipid metabolism both in the steady state (healthy diet) and during feeding of a diet high in lipids, sugar and cholesterol, mimicking that of a typical western diet. This will be performed using our state-of-the-art KC-specific mouse models. In addition, we will profile human KCs isolated from healthy and NASH livers through a partnership with surgeons at the Ghent University Hospital. In this way we aim to identify the common macrophage features underlying murine and human NASH development, which will pave the way towards therapeutic interventions aiming at preventing NASH development in patients with steatosis.