Abstract: SA-PO116

Renal Immune Deposits of Patients with IgA Nephropathy Are Enriched for IgG Autoantibody Specific for Galactose-Deficient IgA1

Session Information

Category: Glomerular

  • 1005 Clinical Glomerular Disorders

Authors

  • Saha, Manish K., University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Rizk, Dana, University of Alabama, Birmingham, Alabama, United States
  • Hall, Stacy D., UAB, Birmingham, Alabama, United States
  • Brown, Rhubell T., University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Novak, Lea, University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Julian, Bruce A., University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Novak, Jan, University of Alabama at Birmingham, Birmingham, Alabama, United States
Background


Patients with IgA nephropathy (IgAN) have circulating immune complexes (ICs) consisting of galactose-deficient IgA1 (Gd-IgA1) bound by Gd-IgA1-specific IgG autoantibodies. Some ICs deposit in the kidney, inciting injury. Renal biopsy examination by routine immunofluorescence reveals IgA, usually with C3 and variably with IgG. We assessed whether patients with IgAN have Gd-IgA1-specific IgG autoantibodies in renal biopsy tissue.

Methods

Frozen remnant renal biopsy specimens from patients with IgAN with (n=5) or without (n=10) IgG glomerular co-deposits (determined by routine immunofluorescence) and a patient with membranous nephropathy (MN; disease control) were used. Tissues were washed with PBS to remove interstitial and blood IgG. IgG from immunodeposits was then extracted by acidic buffer (N Engl J Med 361:11,2009). IgG concentrations were determined by ELISA. IgG molecular integrity was assessed by SDS-PAGE western blots. IgG autoantibodies were determined by their binding to Gd-IgA1 (J Clin Invest 119:1668,2009). Confocal microscopic evaluation was performed using frozen tissue specimens stained with fluorochrome-labeled antibodies specific for IgA, IgG, and C3.

Results


IgG was isolated from washes and extracts of all biopsy specimens, as determined by ELISA and confirmed by western blotting. This finding, suggesting that routine immunofluorescence has low sensitivity and underestimates IgG in immunodeposits, was confirmed by high-resolution confocal microscopy. Line intensity analysis confirmed co-localization of IgA and IgG. Moreover, IgG autoantibodies specific for Gd-IgA1 were detected in extracts of all biopsy specimens from patients with IgAN, but not MN control. Washes had no or very low amounts of IgG autoantibodies.

Conclusion


IgG autoantibodies specific for Gd-IgA1 were detected in renal immunodeposits of patients with IgAN, even in those without IgG by routine immunofluorescence. These findings support the pathogenic significance of IgG autoantibodies in IgAN.

Funding

  • Other NIH Support