Functional differences between hepatocytes and biliary epithelial cells in handling polymeric immunoglobulin A2 in...

Immunoglobulin A (IgA) in bile plays an important role in preventing the biliary tract from infection. In the present study, to clarify the functional differences between hepatocytes and biliary epithelial cells (BEC) in handling polymeric IgA2 (pIgA2), the major and important IgA in bile, we have determined in different species the binding characteristics of 125I-labeled pIgA2 to tissue sections of human, rat, and guinea pig livers. We have also examined the binding and transport features of 125I-labeled and gold-labeled pIgA2 in cultured hepatocytes and cultured BEC of rat and guinea pig. Asialofetuin, an asialoglycoprotein, or an antisecretory component antibody was used for determining the binding characteristics of pIgA2 to the cells. Grains of 125I-pIgA2 were morphometrically analyzed. In tissue sections, 125I-pIgA2 was predominantly bound to rat hepatocytes as well as to human and guinea pig BEC. The binding of 125I-pIgA2 to the cells was significantly inhibited by pretreatment with an antisecretory component (SC) antibody (P < .001), but not by preloaded asialofetuin. In cultured cells, labeled pIgA2 was observed binding predominantly to rat hepatocytes and guinea pig BEC as compared with rat BEC and guinea pig hepatocytes (both P < .001), respectively, and gold particles of gold-labeled pIgA2 were localized in the tubulovesicular structures and biliary luminal spaces of those cells. These results suggested that pIgA2 was bound selectively to hepatocytes in the rat liver, and to BEC in the human and guinea pig livers, through the SC but not through an asialoglycoprotein receptor, and was transported transcellularly and secreted into bile.