S. Sakisaka et al., FUNCTIONAL DIFFERENCES BETWEEN HEPATOCYTES AND BILIARY EPITHELIAL-CELLS IN HANDLING POLYMERIC IMMUNOGLOBULIN A2 IN HUMANS, RATS, AND GUINEA-PIGS, Hepatology, 24(2), 1996, pp. 398-406
Immunoglobulin A (IgA) in bile plays an important role in preventing t
he biliary tract from infection, In the present study, to clarify the
functional differences between hepatocytes and biliary epithelial cell
s (BEG) in handling polymeric IgA2 (pIgA2), the major and important Ig
A in bile, we have determined in different species the binding charact
eristics of I-125-labeled pIgA2 to tissue sections of human, rat, and
guinea pig livers. We have also examined the binding and transport fea
tures of I-125-labeled and gold-labeled pIgA2 in cultured hepatocytes
and cultured BEC of rat and guinea pig. Asialofetuin, an asialoglycopr
otein, or an antisecretory component antibody was used for determining
the binding characteristics of pIgA2 to the cells. Grains of I-125-pI
gA2 were morphometrically analyzed. In tissue sections, I-125-pIgA2 wa
s predominantly bound to Pat hepatocytes as well as to human and guine
a pig BEG. The binding of I-125-pIgA2 to the cells was significantly i
nhibited by pretreatment with an antisecretory component (SC) antibody
(P < .001), but not by preloaded asialofetuin. In cultured cells, lab
eled pIgA2 was observed binding predominantly to rat hepatocytes and g
uinea pig BEC as compared with fat BEC and guinea pig hepatocytes (bot
h P < .001), respectively, and gold particles of gold-labeled pIgA2 we
re localized in the tubulovesicular structures and biliary luminal spa
ces of those cells, These results suggested that pIgA2 was bound selec
tively to hepatocytes in the rat liver, and to BEC hr the human and gu
inea pig livers, through the SC but not through an asialaglycoprotein
receptor, sued was transported transcellularly and secreted into bile.