Expression of programmed death-1 and its ligands in the liver of biliary atresia.

Background: An aberrant immune response is the predominant pathogenetic factor in biliary atresia (BA). Programmed death-1 (PD-1) and its two ligands, programmed death ligand-1 and programmed death ligand-2 (PD-L1 and PD-L2, respectively) play an important inhibitory role in immune reactions. We aimed to illustrate the expression of these molecules in BA.

Methods: Liver specimens were obtained from infants with BA during the Kasai procedure (early BA) and liver transplantation (late BA). Intrahepatic expression of PD- 1, PD-L1, and PD-L2 were examined by immunostaining and compared with that in patients with neonatal hepatitis syndrome and normal controls. The correlation between the expression levels of these molecules in the liver and clinicopathological parameters was analyzed for each group.

Results: Enhanced expression of PD-1 and its ligands occurred in the livers with early BA. In the BA-affected livers, PD-1 was correlated with the degree of peri-biliary inflammation, while PD-L2 was linked more directly with portal fibrosis. None of the three molecules was correlated with the prognosis of the Kasai procedure in patients with early BA.

Conclusions: Only PD-1 and PD-L1 are involved in the immune reactions of early BA. Elucidation of the detailed role of PD-L2 in BA requires further research.