Lectins are
proteins with specificity of binding to certain
monosaccharides or
oligosaccharides. They can detect abnormal glycosylation patterns on
immunoglobulins in patients with various chronic inflammatory diseases, including
rheumatoid arthritis and
IgA nephropathy (IgAN). However,
lectins exhibit binding heterogeneity, depending on their source and methods of isolation. To characterize potential differences in recognition of terminal N-
acetylgalactosamine (GalNAc) on
IgA1, we evaluated the binding characteristics of several commercial preparations of GalNAc-specific
lectins using a panel of
IgA1 and, as controls,
IgA2 and
IgG myeloma proteins. These
lectins originated from snails Helix aspersa (HAA) and Helix pomatia (HPA), and the plant Vicia villosa (VV). Only HAA and HPA bound exclusively to
IgA1, with its O-linked
glycans composed of GalNAc,
galactose, and
sialic acid. In contrast, VV reacted with
sugars of both
IgA subclasses and
IgG, indicating that it also recognized N-linked
glycans without GalNAc. Furthermore, HAA and HPA from several manufacturers differed in their ability to bind various
IgA1 myeloma proteins and other GalNAc-containing
glycoproteins in ELISA and Western blot. For serum samples from IgAN patients, HAA was the optimal
lectin to study
IgA1 glycosylation in ELISA and Western blot assays, including identification of the sites of attachment of the aberrant
glycans. The
galactose-deficient
glycans were site-specific, localized mostly at Thr228 and/or Ser230. Because of the heterogeneity of GalNAc-specific
lectins, they should be carefully characterized with appropriate substrates before undertaking any study.