Objective: To examine O-linked glycosylation of serum IgA1 in children with acute Henoch-Schönlein purpura (HSP).
Methods: The O-linked oligosaccharides of serum IgA1 from 28 children with acute HSP and 26 control children were examined by enzyme immunoassay using plant lectins with well defined carbohydrate binding specificities. The lectins included Artocarpus integrifolia (jacalin), Arachis hypogaea (peanut lectin), and Sambucus nigra (elderberry lectin). Jacalin binds to galactose-N-acetylgalactosamine (Gal-GalNAc). Jacalin interaction with this oligosaccharide is not influenced by the presence of sialic acid on the galactose moiety. Peanut lectin also interacts with Gal-GalNAc, but binding is inhibited if the galactose residue is sialylated. Elderberry lectin binds to N-acetylneuraminic acid (sialic acid).
Results: There was no difference in the binding of jacalin to IgA1 from patients with HSP compared to controls (p = 0.5). The binding of peanut lectin to IgA1 was significantly higher in HSP compared to controls (p = 0.007). Since peanut lectin binding is inhibited by the presence of sialylated galactose, these results suggest diminished sialic content of the O-linked oligosaccharides of IgA1 in HSP compared to controls. Indeed, the binding of the sialic acid-specific elderberry lectin to IgA1 was significantly lower in HSP compared to controls (p = 0.004).
Conclusion: The O-linked oligosaccharides of serum IgA1 from children with acute HSP are deficient in salic acid compared to serum IgA1 from control children.