Abstract
This study was aimed at investigating the clinical significance of serum galactose-deficient IgA1 (Gd-IgA1) levels measured by a novel lectin-independent enzyme-linked immunosorbent assay (ELISA) using an anti-Gd-IgA1 monoclonal antibody (KM55) as a disease-specific biomarker for IgA nephropathy (IgAN) in children. Thirty-three children with IgAN, 40 with non-IgA glomerular diseases, and 38 age-matched healthy controls (HCs) were enrolled. Serum Gd-IgA1 levels were quantified by ELISA using KM55. Results were statistically compared with clinical features and pathological findings of IgAN. Serum Gd-IgA1 levels were significantly elevated in children with IgAN compared with children with non-IgA glomerular diseases and HCs. Serum Gd-IgA1 levels in children with IgAN were positively correlated with serum total IgA levels. However, the serum Gd-IgA1/total IgA ratio (Gd-IgA1/IgA) was also significantly elevated in children with IgAN. Serum Gd-IgA1 levels in children with IgAN increased in an age-dependent manner. The cutoff value of serum Gd-IgA1 levels for differentiating IgAN from non-IgA glomerular diseases was 3236 in children < 12 years and 5284 in children ≥ 12 years, respectively. In contrast, serum Gd-IgA1/IgA was age-independent. The cutoff value of serum Gd-IgA1/IgA for differentiating IgAN from non-IgA glomerular diseases was 0.2401. Serum Gd-IgA1 levels were negatively correlated with eGFR and positively correlated with mesangial IgA deposition. In contrast, serum Gd-IgA1/IgA levels were not correlated with any clinical parameters of IgAN. In conclusion, serum Gd-IgA1 levels were significantly elevated in children with IgAN. However, those levels were age-dependent; therefore, serum Gd-IgA1 levels classified by age and/or serum Gd-IgA1/IgA might have diagnostic values in children with IgAN.
Highlights
IgA nephropathy (IgAN) is the most common form of glomerular disease worldwide in children [1]
Serum GdIgA1 levels were significantly elevated in patients with lupus nephritis (LN) (4570 ng/ml, 1820–12022 ng/ml) compared with patients with minimal change (MC) (p < 0:01) and healthy controls (HCs) (p < 0:05)
Previous studies using conventional lectin assays showed that serum galactose-deficient IgA1 (Gd-IgA1) levels were significantly elevated in children with IgAN and serum Gd-IgA1 levels can differentiate IgAN from other kidney diseases and could serve as a powerful diagnostic approach for diagnosing IgAN [7,8,9]
Summary
IgA nephropathy (IgAN) is the most common form of glomerular disease worldwide in children [1]. The main histopathological lesion characteristic of IgAN is IgA-dominant immunoglobulin deposits, which are often localized in the renal mesangial area [1]. O-glycosylation of IgA1 requires the addition of N-acetylgalactosamine (GalNAc) to serine or threonine residues of the IgA1 hinge region, followed by the addition of galactose [5]. The underlying process has not been completely understood, impaired modifications of the IgA1 chain due to the abnormal expression or activity of glycosyltransferase make the O-glycosylated part of the IgA1 heavychain hinge region lack galactose and expose GalNAc residues [4]. This process results in the formation of circulating immune complexes. Some complexes are deposited in the glomerular mesangium [5], subsequently
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