The expression of galactose on IgA paraproteins from patients with multiple myeloma

Abstract

IgA myeloma for patients is considered prognostically unfavourable. Also, certain IgA myeloma difficulties are related to structural characteristic of monoclonal IgA. Myeloma IgA express O- and N-linked glycans, but their glycans can be different from those expressed on IgA of healthy people. It was reported that loss of Gal residue of the IgA hinge region results in IgA deposits and nephropathy. The monoclonal IgA were detected by agarose gel electrophoresis and identified by immunoelectrophoresis. To assess polymerization and galactose expression, IgA was isolated from myeloma patients by affinity chromatography on Protein M agarose. Isolated proteins were analysed by non-reducing SDS-PAGE and all isolates contained multiple protein fractions with the most intensely coloured fractions representing IgA monomers and dimers. Western blot was used to confirm the presence of IgA monomer and dimers, but also the presence of incomplete IgA molecules (intermediary of IgA synthesis or degraded IgA molecules) in all samples. Expression of galactose on IgA was assessed by lectin blot with a D-galactose-binding lectin, Ricinus communis lectin I (RCA-I). The result showed that galactose was expressed on both monomeric and dimeric IgA. In some isolates galactose is expressed only on monomeric form while in other isolates galactose is strongly expressed on IgA dimer but its expression on monomeric form was weak. This heterogeneity underscores the structural diversity of IgA in myeloma. Understanding its impact on disease progression necessitates correlating structural features with clinical data.