Bilirubin-induced cytomorphological changes in guinea-pig leucocytes

The in vitro influence of bilirubin on guinea-pig peritoneal exudate cells was investigated at concentrations comparable to the conditions of neonatal hyperbilirubinaemia. In in vitro cultures of granulocytes and macrophages bilirubin manifested itself macroscopically by yellow colouring and microscopically by bilirubin aggregation near the nucleus. The intracellular bilirubin content was determined to be 40 nmol per 3 . 10(7) cells. The deposit of bilirubin was irreversible even after subsequent incubation with albumin. Subsequent incubation in heat-inactivated serum reverses binding of bilirubin to cells. Moreover, adding serum to the bilirubin sample prevents the influx of bilirubin. Simultaneously with the deposition of bilirubin there were conspicuous cytomorphological changes in the granulocytes and macrophages observed. The changes consist in a large number of rigid plasma extensions on the whole cell surface. The morphological changes were also reversible by subsequent incubation with serum and their formation was prevented by addition of serum. Since albumin as a well known bilirubin binding protein could not prevent the deposition of bilirubin or the morphological changes, it is suggested that serum factors can regulate the transport of bilirubin across cell membranes.