Abstract: TH-PO042

O-Glycan Profiling of High Molecular Weight Forms of IgA1 in Archival Plasma Samples from IgAN Patients and Controls

Session Information

Category: Glomerular

  • 1001 Glomerular: Basic/Experimental Immunology and Inflammation

Authors

  • Lardinois, Olivier, UNC Kidney Center, Chapel Hill, North Carolina, United States
  • Henderson, Candace Dione, UNC Kidney Center, Chapel Hill, North Carolina, United States
  • Poulton, Caroline J., UNC Kidney Center, Chapel Hill, North Carolina, United States
  • Nachman, Patrick H., UNC Kidney Center, Chapel Hill, North Carolina, United States
Background

IgA nephropathy (IgAN) is the most common form of glomerulonephritis worldwide. The hallmark of the disease is deposition of IgA1 in the glomerular mesangium. These deposited IgA1 are mainly polymeric in nature. Serum polymeric forms of IgA1 are diverse and may include homodimeric IgA, homodimeric secretory IgA, and heterodimeric complexes of IgA covalently bound to other plasma proteins. Abnormalities in O-glycosylation of circulating IgA1, resulting in increased Tn antigen, are hypothesized to be involved in IgAN pathogenesis, and O-glycan structures of monomeric and homodimeric form of IgA1 have been described before in great details. However, so far, very little information is available concerning the O-glycosylation patterns of heterodimeric and other polymeric forms of IgA1 present in the circulation of IgAN patients.

Methods

IgAs were affinity purified from serum samples from 16 patients with IgAN and 16 control subjects. Various molecular forms of IgA1 were size-separated by gel electrophoresis. Proteins were either visualized by Coomassie blue staining or transferred to nitrocellulose membranes for Western blotting. IgA1-containing bands were in-gel digested with trypsin, and the released glycopeptides were analyzed by electrospray ionization liquid mass spectrometry.

Results

Approximately 25 % of IgA1 in archival samples from IgAN patients and controls was found as high molecular mass complexes linked through disulfide bonds. Immunobloting demonstrated 1:1 complexes between IgA and albumin, alpha-1-antitrypsin, or alpha-1-microglobulin. Quantitative analysis of O-linked glycosylation showed no significant differences in glycan composition between different types of circulating IgA1 complexes and no significant difference between glycan composition of IgA1 complexes from IgAN patients and from healthy controls.

Conclusion

These data indicate that, in addition to homodimeric forms of IgA, a significant fraction of IgA1 molecules in the circulation of IgAN patients and healthy controls exist as heterodimeric complexes of IgA covalently bound to other plasma proteins. It is still unclear to what extend the galactose-deficient IgA present in these heterodimeric complexes play a role in the pathogenesis of IgA nephropathy.

Funding

  • NIDDK Support