Underglycosylation of IgA1 hinge plays a certain role for its glomerular deposition in IgA nephropathy

This study was performed to isolate and investigate the IgA1 that could acc umulate in glomeruli (glomerulophilic IgA1). IgA1 was fractionated by the e lectric charge and the reactivity to Jacalin. Serum IgA1 of IgA nephropathy patients was separated and fractionated using a Jacalin column and subsequ ent ion-exchange chromatography. The fractions were divided into three grou ps of relatively cationic (C), neutral (N), and anionic (A). IgA1 was also divided into Jacalin low (L), intermediate (I), and high (H) affinity fract ions by serial elution using 25, 100, and 800 mM galactose. The left kidney s of Wistar rats were perfused with 2, 5, or 10 mg of each group of IgA1. T he rats were sacrificed 15 min, 30 min, 3 h, or 24 h after the perfusion. T he accumulation of each IgA1 in the glomeruli was then observed by immunofl uorescence. The IgA1 of the fractions N and H separated by the two methods was definitely accumulated in the rat glomeruli with a similar pattern. The electrophoresis revealed that the macromolecular IgA1 was increased in fra ction H compared with other fractions. Therefore, Jacalin high-affinity IgA 1 (fraction H) was applied on a diethylaminoethyl column and divided into e lectrically cationic (HC), neutral (HN), and anionic (HA). Only the asialo- Gal beta 1,3GalNAc chain was identified in the fraction HN IgA1 by gas-phas e hydrazinolysis. Furthermore, the IgA1 fraction was strongly recognized by peanut agglutinin, Vicia Villosa lectins, and antisynthetic hinge peptide antibody. These results indicated that the IgA1 molecules having the underg lycosylated hinge glycopeptide played a certain role in the glomerular accu mulation of IgA1 in IgA nephropathy.