To characterize the physiology of circulating IgA immune complexes (IgA-IC), the dynamics of IgA-IC removal by the liver were examined. After intravenous injection, covalently cross-linked IgA antibodies to the dinitrophenyl determinant were rapidly removed from the circulation by the liver. Immunofluorescence microscopy and light and electron microscope autoradiography showed that the IgA-IC were associated with Kupffer cells. With increasing doses of injected IgA-IC the clearance velocity approached a maximum, thus prolonging the circulation of IgA-IC. All these observations indicated a receptor-mediated process. Saturating doses of various potential receptor-blocking agents, heat-aggregated mouse IgG, microaggregated human serum albumin, and purified dimeric IgA did not influence the clearance pattern and hepatic uptake of radiolabeled IgA-IC. Mouse livers were also perfused via the portal vein with 1 microgram of IgA-IC. In the presence or absence of serum proteins, 43% of the perfused IgA-IC were removed in a single passage. This liver uptake was not reduced with simultaneous perfusion of large doses of aggregated mouse IgG, aggregated human serum albumin, or purified free dimeric mouse IgA. In contrast, the liver uptake of radiolabeled IgA-IC was decreased by 88% with the addition of 1 mg unlabeled IgA-IC. These observations support the conclusion that removal of IgA-IC from circulation is mediated by a specific IgA receptor on Kupffer cells.

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