Impaired polymorphonuclear leukocyte function in biliary atresia: role of bilirubin and bile acids

Our previous study suggested that impaired bactericidal activity of polymorphonuclear leukocytes in patients with biliary atresia might be due to decrease in superoxide-generating activity and that serum factors may play an important role. In the present study, analysis of the patients' serum revealed that, among 15 bile acids, glycine or taurine conjugated chenodeoxycholic acid and cholic acid were markedly elevated. To examine the effects of bilirubin and these bile acids and conjugated lithocholic acids on the leukocyte function, we measured cytolysis, phorbol myristate acetate-induced superoxide generation, and myeloperoxidase activity, using normal human polymorphonuclear leukocytes. Bilirubin ranging from 5 to 20 mumol/L was cytolytic and more potently inhibited the superoxide generation. The inhibition by bilirubin was also observed in the presence of 10% human serum or 2.0% human serum albumin, though the cell viability was almost completely preserved. On the other hand, conjugated chenodeoxycholic acids and cholic acids, ranging from 0.5 to 1.5 mmol/L or conjugated lithocholic acids, ranging from 0.02 to 0.05 mmol/L, did not inhibit the superoxide generating activity, though the conjugated chenodeoxycholic acids and lithocholic acids did induce cytolysis. Myeloperoxidase activity was little affected, except in the case of conjugated lithocholic acids. These results suggest that in patients with biliary atresia, bilirubin, probably the unconjugated form, more than bile acids might be one of the influential factors in the suppression of bactericidal activity of polymorphonuclear leukocytes, by inhibiting the superoxide-generating activity.