Similarities between N-glycan glycoform of tonsillar IgA1 and that of aberrant IgA1 abundant in IgA nephropathy patient serum.

Background: There are many reports on the presence of an incompletely glycosylated O-linked oligosaccharide(s) in the IgA1 hinge region of some IgA nephropathy patients. As the candidates of such IgA1, tonsillar IgA1 and aberrant IgA1, which are abundant in an IgA nephropathy patient, were proposed. On the other hand, in mice, the abnormality of the N-linked oligosaccharide chain of IgA induced the IgA nephropathy. Therefore, analyses of the N-glycan glycoform on serum IgA1, aberrant IgA1 and tonsillar IgA1 were carried out using the 3-dimensional mapping method.

Results: The sugar chain composition was almost the same in these 3 IgA1 preparations. However, the structural characteristics for the aberrant IgA1 showed a drastic increase in the neutral N-glycans; in particular, 25% of the sugar chains in the aberrant IgA1 were the high mannose-type as compared with approximately 5%-6% in the serum IgA1 and tonsillar IgA1. The neutral complex-type N-glycan chain with fucose was higher in both the aberrant IgA1 and tonsillar IgA1 than in the serum IgA1. A typical component in the aberrant IgA1 was the fully galactosylated biantenna with the fucose residue.

Conclusions: We found an abnormality in the N-linked oligosaccharides of the aberrant IgA1. In addition to our previous report about the abundance of asialo-O-linked oligosaccharide in both the tonsillar IgA and aberrant IgA, our results concerning the N-glycan glycoform of the aberrant IgA showed the possible promotion of its self-aggregation and its glomerular deposition by the synergistic difference in the O- and N-linked carbohydrate chains, and also the derivation of the aberrant IgA1 in the sera from the tonsillar tissue.