title: IgA nephropathy and Henoch-Schoenlein purpura nephritis: aberrant glycosylation of IgA1, formation of IgA1-containing immune complexes, and activation of mesangial cells.
abstract: IgA1 in the circulation and glomerular deposits of patients with IgA nephropathy (IgAN) is aberrantly glycosylated; the hinge-region O-linked glycans are galactose-deficient. The circulating IgA1 of patients with Henoch-Schoenlein purpura nephritis (HSPN) has a similar defect. This aberrancy exposes N-acetylgalactosamine-containing neoepitopes recognized by naturally occurring IgG or IgA1 antibodies resulting in formation of immune complexes. IgA1 contains up to six O-glycosylation sites per heavy chain; it is not known whether the glycosylation defect occurs randomly or preferentially at specific sites. We sought to define the aberrant glycosylation of a galactose-deficient IgA1 myeloma protein and analyze the formation of the immune complexes and their biological activities. Supplementation of serum or cord-blood serum with this IgA1 protein resulted in formation of new IgA1 complexes. These complexes stimulated proliferation of cultured human mesangial cells, as did the naturally-occurring IgA1-containing complexes from sera of patients with IgAN and HSPN. Uncomplexed IgA1 did not affect cellular proliferation. Using specific proteases, lectin Western blots, and mass spectrometry, we determined the O-glycosylation sites in the hinge region of the IgA1 myeloma protein and IgA1 proteins from sera of IgAN patients. The IgA1 myeloma protein had galactose-deficient sites at residues 228 and/or 230 and 232. These sites reacted with IgG specific to galactose-deficient IgA1. IgA1 from the IgAN patients had galactose-deficient O-glycans at the same residues. In summary, we identified the neoepitopes on IgA1 responsible for formation of the pathogenic immune complexes. These studies may lead to development of noninvasive diagnostic assays and future disease-specific therapy.
authors.affiliation: University of Alabama at Birmingham, Department of Microbiology, Birmingham, AL 35294, USA. jannovak@uab.edu
authors.forename: Jan
authors.initials: J
authors.lastname: Novak
authors.forename: Zina
authors.initials: Z
authors.lastname: Moldoveanu
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Renfrow
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yanagihara
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Milan
authors.initials: M
authors.lastname: Raska
authors.forename: Stacy
authors.initials: S
authors.lastname: Hall
authors.forename: Rhubell
authors.initials: R
authors.lastname: Brown
authors.forename: Wen-Qiang
authors.initials: WQ
authors.lastname: Huang
authors.forename: Alice
authors.initials: A
authors.lastname: Goepfert
authors.forename: Mogens
authors.initials: M
authors.lastname: Kilian
authors.forename: Knud
authors.initials: K
authors.lastname: Poulsen
authors.forename: Milan
authors.initials: M
authors.lastname: Tomana
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Wyatt
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Julian
authors.forename: Jiri
authors.initials: J
authors.lastname: Mestecky
mesh_terms: D000936:Antigen-Antibody Complex / Q000276:immunology*; D005920:Glomerular Mesangium / Q000276:immunology / Q000378:metabolism; D005922:Glomerulonephritis, IGA / Q000276:immunology*; D006031:Glycosylation; D006801:Humans; D011695:IgA Vasculitis / Q000150:complications / Q000276:immunology*; D007070:Immunoglobulin A / Q000276:immunology / Q000378:metabolism*; D009393:Nephritis / Q000209:etiology / Q000276:immunology*
chemical_list: D000936:Antigen-Antibody Complex; D007070:Immunoglobulin A