TNFRSF9 and autoimmune hepatitis: Intrahepatic CD8+ T cells were characterized by a significantly higher frequency of cells expressing PD-1 in AIH untreated group, compared to Normal (57.4 ± 4.2% vs. 17.0 ± 3.1%, p < 0.0001), the same as a higher frequency of CD8+ T cells expressing 4-1BB+ (8.1 ± 2.0% vs. 1.5 ± 0.4%, p = 0.0011, Figure 2a,b).