To further explore the mechanisms underlying the loss of tolerance to liver antigens in AIH, we here investigate a new mouse model that is characterized by hepatocellular expression of an MHC class II–restricted immunodominant T cell epitope of the lymphocytic choriomeningitis virus (GP61–80), and by abundance of cognate CD4 T cells recognizing GP61–80 expressed by hepatocytes. This evidence concerns the gene CD4 and autoimmune hepatitis.