Kidney Week

Abstract: TH-PO0269

Galactose-Deficient IgA1-IgG-Containing Immune Complexes (IC) Require Activated Complement C3 to Induce Cellular Proliferation of Cultured Primary Human Mesangial Cells

Session Information

• Glomerular Diseases: Cell Biology
  October 22, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology

Authors

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

Stacy D. Hall, MPH

• Hirayama, Masaya, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Masaya Hirayama, PhD

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

Zhi qiang Huang

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

Zina Moldoveanu, PhD

• Qiu, Shihong, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Shihong Qiu

• Shang, Qiao, The University of Alabama at Birmingham, Birmingham, Alabama, United States

Qiao Shang

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

Dana V. Rizk, MD

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

Bruce A. Julian, MD

• Green, Todd J., The University of Alabama at Birmingham, Birmingham, Alabama, United States

Todd J. Green, PhD

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

Jan Novak, PhD

Background

IgA nephropathy (IgAN) is an IC-associated mesangioproliferative glomerulonephritis. The glomerular IC deposits, comprised of galactose-deficient IgA1 (Gd-IgA1), Gd-IgA1-specific IgG autoantibodies, and complement C3, likely originate from the circulation. Elevated C3-IgA colocalization is associated with mesangial hypercellularity. We have previously shown that Gd-IgA1 added to IgAN-patient serum is bound by IgG autoantibodies to form additional IC with activated C3 (i.e., C3(H₂O) and C3b). However, it is unknown whether one or both forms of activated C3 can support mesangioproliferative activity of Gd-IgA1-IgG IC. To address this gap in knowledge, we analyzed the size, compositions and biological activity of IC formed using recombinant polymeric Gd-IgA1 and recombinant IgG autoantibodies in healthy individuals’ C3-depleted sera and supplemented with either C3 or C3b.

Methods

IC were formed in vitro from recombinant polymeric Gd-IgA1 and recombinant IgG autoantibody in C3-depleted serum supplemented with either C3 or C3b and isolated by size-exclusion chromatography as fractions F1-F8 (Mr ~4 MDa to 0.7 MDa). C3-depleted serum served as a negative control. Biological activity of fractions was determined using click-iT EdU cell-proliferation assay and cultured primary human mesangial cells. IC composition was analyzed by ELISA (IgA and IgG-IgA, C3-IgA, and C3-IgG IC); mAb 3E7 [binds C3b, iC3b, and C3(H₂O) but not C3 with intact thioester bond] capture was used to detect IgA or IgG IC with activated C3.

Results

IC-supplemented C3- or C3b-repleted sera had elevated IgA concentrations in fractions F6-F8. IC in C3-repleted serum had proliferation-inducing activity in F6-F8. IC in C3b-repleted serum had proliferation-inducing activity in F5 and F8. Individual purified proteins (Gd-IgA1, IgG, C3, or C3b) had little or no proliferation-inducing activity. IgG-IgA IC were detected in F3-F8 of C3- and C3b-repleted sera. C3-IgA and C3-IgG IC were detected in F3-F8 of C3- and C3b-repleted sera, with lower amounts in F5-F8 of C3b-repleted serum. 3E7-C3 and 3E7-IgA IC showed greater IC amounts in C3-repleted vs. C3b-repleted serum.

Conclusion

Gd-IgA1-IgG IC requires activated C3 for their pathogenic activity. Although C3 [as C3(H₂O)] and C3b can provide similar functions, the size and amounts of the resultant IC may vary.

Acknowledgment

This project was supported in part by research-acceleration funds from the University of Alabama at Birmingham, by a gift from IGA Nephropathy Foundation, and the NIH.

Funding

• NIDDK Support