Aims: Investigate the role of the apelin/APLNR axis in metabolic dysfunction-associated steatotic liver disease (MASLD), focusing on the progression from metabolic dysfunction-associated simple steatotic liver (MASS) to metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis, with emphasis on liver B cells. The gene discussed is APLN; the disease is metabolic dysfunction-associated steatohepatitis.