INTRODUCTION: Immunoglobulin A1 (IgA1) with galactose-deficient O-glycans (Gd-IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). Mucosal-tissue infections increase IL-6 production and, in patients with IgAN, are often associated with macroscopic hematuria. IgA1-secreting cell lines derived from the circulation of patients with IgAN, compared to those of healthy controls (HCs), produce more IgA1 that has O-glycans with terminal or sialylated N-acetylgalactosamine (GalNAc). GalNAc residues are added to IgA1 hinge region by some of the 20 GalNAc transferases, the O-glycosylation-initiating enzymes. Expression of GALNT2, encoding GalNAc-T2, the main enzyme initiating IgA1 O-glycosylation, is similar in cells derived from patients with IgAN and HCs. In this report, we extend our observations of GALNT14 overexpression in IgA1-producing cell lines from patients with IgAN. METHODS: GALNT14 expression was analyzed in peripheral blood mononuclear cells (PBMCs) from patients with IgAN and from HCs. Moreover, the effect of GALNT14 overexpression or knock-down on Gd-IgA1 production in Dakiki cells was assessed. RESULTS: GALNT14 was overexpressed in PBMCs from patients with IgAN. IL-6 increased GALNT14 expression in PBMCs from patients with IgAN and HCs. We used IgA1-producing cell line Dakiki, a previously reported model of Gd-IgA1-producing cells, and showed that overexpression of GalNAc-T14 enhanced galactose deficiency of IgA1, whereas siRNA-mediated GalNAc-T14 knock-down reduced it. GalNAc-T14 was localized in trans-Golgi network, as expected. CONCLUSIONS: Overexpression of GALNT14 due to inflammatory signals during mucosal infections may contribute to overproduction of Gd-IgA1 in patients with IgAN.

• Keywords
• GalNAc-T14, IL-6 cytokine, IgA nephropathy, inflammation,
• Publication type
• Journal Article MeSH

BACKGROUND: IgA nephropathy (IgAN) primary glomerulonephritis is characterized by the deposition of circulating immune complexes composed of polymeric IgA1 molecules with altered O-glycans (Gd-IgA1) and anti-glycan antibodies in the kidney mesangium. The mesangial IgA deposits and serum IgA1 contain predominantly λ light (L) chains, but the nature and origin of such IgA remains enigmatic. METHODS: We analyzed λ L chain expression in peripheral blood B cells of 30 IgAN patients, 30 healthy controls (HCs), and 18 membranous nephropathy patients selected as disease controls (non-IgAN). RESULTS: In comparison to HCs and non-IgAN patients, peripheral blood surface/membrane bound (mb)-Gd-IgA1+ cells from IgAN patients express predominantly λ L chains. In contrast, total mb-IgA+, mb-IgG+, and mb-IgM+ cells were preferentially positive for kappa (κ) L chains, in all analyzed groups. Although minor in comparison to κ L chains, λ L chain subsets of mb-IgG+, mb-IgM+, and mb-IgA+ cells were significantly enriched in IgAN patients in comparison to non-IgAN patients and/or HCs. In contrast to HCs, the peripheral blood of IgAN patients was enriched with λ+ mb-Gd-IgA1+, CCR10+, and CCR9+ cells, which preferentially home to the upper respiratory and digestive tracts. Furthermore, we observed that mb-Gd-IgA1+ cell populations comprise more CD138+ cells and plasmablasts (CD38+) in comparison to total mb-IgA+ cells. CONCLUSIONS: Peripheral blood of IgAN patients is enriched with migratory λ+ mb-Gd-IgA1+ B cells, with the potential to home to mucosal sites where Gd-IgA1 could be produced during local respiratory or digestive tract infections.

• Keywords
• B lymphocytes, IgA nephropathy, galactose, galactose-deficient IgA1, immunoglobulin A, immunoglobulin lambda chains, immunology,
• MeSH
• Galactose MeSH
• Glomerulonephritis, IGA * MeSH
• Immunoglobulin A metabolism   MeSH
• Immunoglobulin G MeSH
• Immunoglobulin M MeSH
• Humans MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Galactose MeSH
• Immunoglobulin A MeSH
• Immunoglobulin G MeSH
• Immunoglobulin M MeSH