Repertoire of human natural anti-glycan immunoglobulins. Do we have auto-antibodies?

BackgroundProfiling of donor's antibodies using glycan arrays demonstrated presence of antibodies capable of binding to > 100 mammalian glycans or their fragments. For example, relatively high binding to Galα1-4Galβ1-4GlcNAc (P1), Galα1-4Galβ1-4Glc (Pk), Galβ1-3GlcNAc (Lec), 4-O-SuGalβ1-4GlcNAc, and GalNAcα1-3GalNAc (Fs) was found in all tested individuals. Affinity isolation using hapten-specific chromatography in combination with epitope mapping revealed their glycotopes. Notably, a significant part of the antibodies was capable of recognizing a fragment of larger glycans, for example, -Galβ1-4Glc of glycolipids, or Fucα1-3GlcNAc motif of LeX/LeY antigens. Their epitope specificity did not vary between different healthy individuals. Nominally, all the mentioned immunoglobulins could be classified as auto-antibodies.MethodsIn this work we re-evaluated results published earlier and analyzed new data to address the question why autologous antibodies found in healthy individuals do not cause severe auto-immune reactions.ResultsIn all cases the presumably “auto” antibodies were found to bind short fragments “subtracted” from larger glycans whereas recognition of the same fragment in the context of the whole natural chain was completely abolished. Thus, in spite of numerous formally positive signals observed on the printed glycan array, we are yet unable to identify in blood serum of healthy individuals true auto-antibodies capable of binding carbohydrate chains in their naturally occurring form.General significanceThe identified natural anti-glycan antibodies were found to be specific, high-titer and population conservative immunoglobulins — all of this suggesting as yet unknown biological role(s) of the studied proteins. This article is part of a Special Issue entitled Glycoproteomics.

► Printed glycan array demonstrates presence of Ab to > 100 mammalian glycans.
► Found Ab are specific, high-titer and population conservative immunoglobulins.
► ~30% of found Ab recognize core (hidden, inner part) of larger glycans.
► Identified auto-Ab are incapable of recognizing cognate glycans on cell surface.
► New species of natural Ab bind antennary polylactosamine N-chains.