Kidney Week

Abstract: SA-PO641

Biologically Active Circulatory Immune Complexes in IgA Nephropathy Contain Polymeric IgA1, With Galactose-Deficient and Minimally Sialylated O-Glycans, IgG, and Complement C3b and iC3b

Session Information

• Glomerular Diseases: IgA and Complement-Mediated GN
  November 05, 2022 | Location: Exhibit Hall, Orange County Convention Center‚ West Building
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1302 Glomerular Diseases: Immunology and Inflammation

Authors

• Hall, Stacy D., The University of Alabama at Birmingham, Birmingham, Alabama, United States

Stacy D. Hall,

• Coffee, Sarah, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Sarah Coffee,

• Huang, Zhi qiang, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Zhi qiang Huang,

• Maillard, Nicolas, The University of Alabama at Birmingham, Birmingham, United States

Nicolas Maillard,

• Moldoveanu, Zina, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Zina Moldoveanu,

• Hargett, Audra A., The University of Alabama at Birmingham, Birmingham, Alabama, United States

Audra A. Hargett,

• Rizk, Dana, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Dana Rizk,

• Julian, Bruce A., The University of Alabama at Birmingham, Birmingham, Alabama, United States

Bruce A. Julian,

• Renfrow, Matthew B., The University of Alabama at Birmingham, Birmingham, Alabama, United States

Matthew B. Renfrow,

• Novak, Jan, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Jan Novak,

Background

IgA nephropathy (IgAN) is an autoimmune disease wherein pathogenic immune complexes (IC) are thought to form in the circulation from IgA1 with some hinge-region O-glycans deficient in galactose (galactose-deficient IgA1; Gd-IgA1) bound by IgG autoantibodies. Some of these IC deposit in the glomeruli to induce kidney injury. The glomerular immunodeposits are enriched for Gd-IgA1 and the corresponding IgG autoantibodies. However, the composition of the circulating IC in IgAN is not fully understood.

Methods

We isolated different molecular forms of IgA1 from sera of 20 patients with IgAN by lectin-affinity and size-exclusion chromatography (SEC). Isolated monomeric IgA1 (mIgA1), polymeric IgA1 (pIgA1), and IgA1 bound in IC (IgA1-IC) were analyzed for their degree of galactose deficiency by a lectin ELISA performed without and with neuraminidase treatment to remove sialic acid. For assessment of biological activity, IgA1-IC were isolated by SEC directly from serum and tested for proliferation-stimulating and signaling-inducing activities in cultured primary human mesangial cells. SDS-PAGE immunoblotting was used for detection of IgA, IgG, complement C3, and phosphorylated (P-) and total ERK1/2, and P- and total Akt.

Results

Molecular forms of serum IgA1 included mIgA1 (~90%), pIgA1 (~9%) and IgA1-IC (<0.4%). Relative degree of galactose deficiency of the IgA1 was highest in IgA1-IC, less in pIgA1, and least in mIgA1. IgA1 in IC had minimally sialylated O-glycans. IgA1-IC isolated by SEC from sera of IgAN patients had molecular mass >700 kDa. These circulatory IC induced signaling (e.g., P-ERK1/2, P-Akt) and cellular proliferation of the mesangial cells. These biologically active IgA1-IC contained pIgA1, IgG, and complement C3b and iC3b.

Conclusion

Biologically active circulatory immune complexes in patients with IgAN had molecular mass >700 kDa and contained polymeric Gd-IgA1 with a high degree of galactose deficiency and minimal sialylation, IgG, C3b, and iC3b. Collectively, these findings support the pathogenic role of IgA1-containing immune complexes in IgAN.

Funding

• NIDDK Support