Delayed clearance of specific polymeric IgA immune complexes in patients with IgA nephropathy

The presence of multimeric (polymeric and monomeric) IgA immune complexes (IC), detected by Raji cell assay and by the inhibition binding assay, as well as the specific polymeric IgA-IC were examined before and after the ingestion of 100 g protein. A rise in multimeric IgA-IC occurred in three out of seven controls with a peak at two to four hours after the meal, being cleared thereafter. The amount of multimeric IC present at fasting in four of six patients diminished at two to four hours after food challenge reaching a new peak around six hours. In both controls and patients, IC containing antibodies against diet antigens (e.g. ovalbumin) paralleled those of multimeric IgA-IC. In controls the specific polymeric IgA-IC presented a maximal peak with distribution similar to multimeric IgA-IC, but with a faster disappearance from the circulation. By contrast, polymeric IgA-IC remained elevated 24 hours after food ingestion in most patients. These results suggest that a defect in the hepatic clearance of circulating polymeric IgA-IC exists in patients with IgA nephropathy.