The potential immunosuppressive effect of bilirubin

The effect of bilirubin on the cells of the immune system was studied using various in vitro and in vivo systems. Bilirubin was found to inhibit the in vitro chemotactic (migratory) activity of human granulocytes; on the other hand, a temporary stimulation of phagocytic activity of both granulocytes and monocytes was found in mice injected with a single i.p. injection of bilirubin. Continuous i.v. infusion of bilirubin produced a significant decrease of antibody (plaque) forming cells in the spleens of mice immunized with sheep red blood cells. In newborns suffering from hyperbilirubinaemia, enhanced proportion of "activated" lymphocytes occurred. Finally, bilirubin possessed a significant in vitro cytotoxic effect in human adult and newborn blood lymphocytes and granulocytes. A brief survey of so far known immunological effects of bilirubin is discussed.