One of the best studied posttranslational modification of immunoglobulin G (IgG) is the addition of a complex glycan to asparagine 297, which is required for IgG to bind to Fc-receptors and for the activation of complement via the classical activation pathway. In the absence of the glycan the IgG usually behave like a lame duck unable to execute its effector functions. The sugar tree is polymorphic and there are several functional consequences related to the glycan. The terminal sialylation, the presence of galactose, the core fucosylalation and the insertion of a bisecting third sugar chain all reportedly modify the biological and functional activities of IgG.
As examples for the impact of Asp-297 associated glycans to the activity I will present (I) the sialylation of anti-histon autoantibodies in patients with systemic lupus erythematosus (II) the exposure of sugar epitopes by random IgG isolated from patients with rheumatoid arthritis (III) the molecular analysis of the glycan of random IgG isolated from patients with inflammatory diseases and controls and (IV) and finally the glycosylation of IgG-anti-phospholipid autoantibodies in healthy children.
(I) The autoantibodies are mainly found in the non-sialyated fraction of the anti-histon autoantibodies which can be considered inflammatory IgG.
(II) The circulating random IgG from patients with rheumatoid arthritis show an increased exposure of the Asp-297 associated glycans.
(III) The molecular analysis of the glycan of random IgG isolated from patients with systemic lupus erythematosus, rheumatoid arthritis, sepsis showed disease-specific glycans.
(IV) The non-pathogenic IgG-anti-phospholipid autoantibodies isolated from healthy children displayed an increased sialylation when compared to the pathogenic autoantibodies from adults with anti-phospholipid syndrome.
The examples point to a strong impact of IgG glycosylation in the etiopathogenesis of chronic inflammatory rheumatic diseases. One should consider to include IgG glycan analyses into the diagnostic repertoire for autoantibodies.
Disclosure of Interest None declared