Quantitative study of the uptake of IgA by isolated rat hepatocytes

Recently dispersed rat hepatocytes showed high capacity for uptake of monomeric and polymeric human IgA by simple absorptive endocytosis. Maximum uptake exceeded 15 million monomer units per cell. The asialo-glycoprotein receptor was not involved in this process. J chain-containing polymers were on the average taken up somewhat better than monomers and substantially better than J chain-deficient polymers. This result would agree with a partial involvement of the secretory component (SC) in the absorptive uptake of IgA. Different receptor mechanism might hence explain the hepatic transport of IgA from blood to bile in the rat and perhaps be involved in the catabolism of IgA. After binding to the plasma membrane of the rat hepatocyte, most of the human IgA was internalized in endocytic vesicles. A considerable proportion of radiolabelled IgA apparently reached the lysosomes after internalization and became degraded.