Dimeric mouse IgA is transported into rat bile five times more rapidly than into mouse bile

The kinetics of the biliary dimeric IgA transport in rats is well documented from studies on animals with cannulated bile ducts, while in mice such information rests on the analysis of samples periodically removed from the gall bladder and on serum disappearance rates. We have quantitatively compared the kinetics of IgA transport in these two rodents by using affinity-purified radiolabelled monomeric and dimeric M315 IgA which specifically binds dinitrophenyl (DNP). Bile collection procedures, sample analysis, and administration of the radiolabelled M315 were the same for both species, although in mice the cystic duct was ligated to prevent reflux of any bile or IgA from the gall bladder into the common bile duct. A pronounced selection for transport of dimeric M315 was seen in both species. When dimeric M315 was administered, it was recovered in the dimeric form from the bile of both species, and 60-80% could specifically bind to DNP-gelatin. When monomeric M315 was administered, very little was transported, and the IgA recovered in bile had a much lower capacity to bind DNP-gelatin and appeared to be of low molecular weight. Approximately 60% of the intravenously administered dimeric IgA was transported into bile of both species but biliary transport of the heterologous dimeric IgA into rat bile was five times more rapid than the transport of the dimeric M315 into its homologous species, the mouse. Hence, IgA transport in these species is similar in specificity, integrity of the transported IgA and in the percentage cleared, while differing significantly in the rate of transport. This cannot be ascribed to the species source of the IgA.