Selective hepatobiliary transport of human polymeric IgA in mice

Both subclasses of human polymeric IgA (pIgA) were selectively transported from the serum into the bile of mice relative to human IgG or IgM. Removal of human pIgA from serum corresponded to the clearance kinetics shown for murine pIgA. The biliary pIgA was intact as determined by sucrose density gradient ultracentrifugation. This hepatic uptake was specific for the IgA isotype and occurred independently of receptors in the liver specific for glycoproteins that terminate with galactose or mannose moieties. Desialylation of human pIgA resulted in its rapid clearance from serum and subsequent deposition in the liver in a manner similar to most other desialylated serum glycoproteins. The desialylated pIgA present in bile was also an intact molecule; thus the asialoglycoprotein receptor may represent an additional mechanism for the transport of serum pIgA into bile.