Increased N-linked glycosylation leading to oversialylation of monomeric immunoglobulin A1 from patients with Sjögren's syndrome

Scand J Immunol. 2000 Mar;51(3):300-6. doi: 10.1046/j.1365-3083.2000.00685.x.

Abstract

Increased serum immunoglobulin A (IgA) level is a common finding in primary Sjögren's syndrome (pSS). IgA might not be properly eliminated because of an abnormal glycosylation. We reported previously that IgA1 from patients with pSS was oversialylated. We extend this finding by showing that monomeric IgA1 contains more sialic acid (SA) in patients than in controls, as determined by enzyme-linked immunosorbent assay (ELISA) and Western blot with Sambucus nigra agglutinin (SNA), a lectin specific for SA. To localize this excess of SA on the N- and/or O-linked oligosaccharides, we analysed them separately, using N- and O-linked oligosaccharide profiling kits based on fluorophore-assisted carbohydrate electrophoresis. N-linked, but not O-linked, oligosaccharides of patients' IgA1 were oversialylated, and this seemed to be linked to an excess of SA on the same number of polysaccharides as normal IgA1. To localize the abnormality to the Fab and/or Fc fragments, monomeric IgA1 was digested with protease, separated and transferred to nitrocellulose, where SA was identified by SNA. Both Fab and Fc fragments appeared to be oversialylated. Oversialylation of N-linked oligosaccharides of IgA1 from patients with pSS might prevent the recognition of IgA by receptors that are responsible for their clearance, resulting in an excess of serum IgA and related immune complexes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Carbohydrate Conformation
  • Carbohydrate Sequence
  • Dimerization
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Glycosylation
  • Humans
  • Immunoglobulin A / metabolism*
  • Immunoglobulin Fc Fragments / metabolism
  • Immunoglobulin Fragments / metabolism
  • Lectins / metabolism
  • Male
  • Middle Aged
  • Molecular Sequence Data
  • N-Acetylneuraminic Acid / metabolism*
  • Oligosaccharides / metabolism
  • Plant Lectins*
  • Ribosome Inactivating Proteins
  • Sjogren's Syndrome / immunology*
  • Sjogren's Syndrome / metabolism*

Substances

  • Immunoglobulin A
  • Immunoglobulin Fc Fragments
  • Immunoglobulin Fragments
  • Lectins
  • Oligosaccharides
  • Plant Lectins
  • Sambucus nigra lectins
  • immunoglobulins, Fd
  • Ribosome Inactivating Proteins
  • N-Acetylneuraminic Acid