Increased sialylation of polymeric λ-IgA1 in patients with IgA nephropathy

✍ Scribed by Joseph C.K. Leung; Sydney C.W. Tang; Daniel T.M. Chan; Sing Leung Lui; Kar Neng Lai

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 349 KB
• Volume: 16
• Category: Article
• ISSN: 0887-8013
• DOI: 10.1002/jcla.2035

✦ Synopsis

The mechanism of mesangial IgA deposition is poorly understood in IgA nephropathy (IgAN). Abnormal glycosylation of carbohydrate moieties in the hinge region of the IgA molecule has recently attracted much attention. In this report, we studied galactosylation and sialylation profiles in κand λ-IgA 1 from patients with IgAN. Total serum IgA 1 was isolated from patients with IgAN or healthy controls by jacalin-affinity chromatography. Six fractions of molecular weight (MW) 50-1,000 kDa were separated by fast protein liquid chromatography (FPLC). Four lectin-binding assays were used to study the sialylation and the presence of terminal galactose or Nacetylgalactosamine (GalNAc) in the Olinked carbohydrate moieties of κor λ-IgA 1 . Maackia amurensis agglutinin (MAA) and Sambucus nigra agglutinin (SNA) lectin recognize α(2,3)and α(2,6)-linked sialic acid, respectively. Peanut agglutinin (PNA) and Helix aspersa (HA) lectin recognize terminal galactose and GalNAc, respectively. Re-duced HA was demonstrated in macromolecular κ or λ-IgA 1 (300-825 kDa) isolated from patients with IgAN (P < 0.05 compared with healthy controls). Lambda-but not κ-IgA 1 from patients with IgAN bound less to PNA (P < 0.05). The α(2,3)-linked sialic acid content in λbut not κ-IgA 1 of MW 150-610 kDa from patients was higher than that of controls (P < 0.005). The α(2,6)-linked sialic acid content in λ-IgA 1 (300-825 kDa) and κ-IgA 1 (150-610 kDa) from patients was also higher than that of controls. This unusual glycosylation and sialylation pattern of the λ-IgA 1 may have important implications for the pathogenesis of IgAN, as both the masking effect of sialic acid on galactose and the reduced galactosylation will hinder the clearance of macromolecular λ-IgA 1 by asialoglycoprotein receptor of hepatocytes. The negative charge from sialic acid may also favor mesangial deposition of macromolecular λ-IgA 1 in IgAN.