Immune complexes in IgA nephropathy: presence of antibodies against diet antigens and delayed clearance of specific polymeric IgA immune complexes.

Several features suggest that IgA nephropathy is an immune complex (IC)-mediated disease. The source of antigen(s) is unknown but the predominant involvement of IgA suggest that it is associated in some way with the gut or respiratory tract. Taking into account the specific hepatobiliary transport by polymeric IgA of circulating antigens entering through the mucosal surfaces we examined the possible involvement of antibodies against food antigens in the circulating IC and the existence of a defect in their blood clearance in patients with IgA nephropathy. A rise in multimeric IgA-IC (Raji assay) occurred in three of seven control subjects with a peak at 2-4 h after food ingestion. The amount of multimeric IgA-IC present at fasting in four out of six patients, diminished 2-4 h after food challenge, reaching a new peak around 6 h. At fasting, three out of six patients had IC containing antibodies against diet antigens (e.g. ovalbumin). These IC paralleled, both in patients and controls, the levels of multimeric IgA-IC. In patients small multimeric IgA-IC predominated at fasting and 24 h after food ingestion, while larger IC were detected at 2-4 h of food challenge. The specific polymeric IgA-IC showed in controls a maximal peak with similar distribution to that of multimeric IgA-IC, but with a quicker disappearance from the circulation. By contrast, polymeric IgA-IC remained elevated 24 h after food ingestion in most patients. These results suggest that antibodies against common antigens are within circulating IC and that a defect in the hepatic clearance of circulating polymeric IgA-IC exists in patients with IgA nephropathy.