**8. Conclusions**

IgAN is characterized by glomerular immunodeposits enriched for Gd-IgA1 glycoforms and for IgG autoantibodies with specificity for the IgA1 with galactose-deficient *O*-glycans. These immunodeposits are thought to originate from Gd-IgA1-IgG complexes formed in the circulation. It was recently shown experimentally that human IgG autoantibodies bind to human Gd-IgA1 to form immune complexes that in a murine model induce pathogenic changes consistent with IgAN. It is hoped that a better understanding of the key players in IgAN, autoantibodies, and autoantigens, will enable development of disease-specific treatments.

**Author Contributions:** All authors participated in the development of the overall concept and outline. Each author was then assigned a specific section to write. B.K. combined all sections and added and formatted references. All authors reviewed and edited the final manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** Supported by NIH grants AI149431, DK078244, DK082753, and DK106341, and a gift from the IGA Nephropathy Foundation of America.

**Conflicts of Interest:** B.A.J. and J.N. are co-inventors on US patent application 14/318,082 (assigned to UAB Research Foundation). B.A.J. and J.N. are co-founders and co-owners of and consultants for Reliant Glycosciences, LLC. Other authors declare no conflict of interest.
