Expression of terminal galactose and sialic acid on serum IgA in IgA multiple myeloma

Abstract

Introduction/Objective IgA multiple myeloma has a poor prognosis, and altered glycosylation of myeloma IgA may be one of contributing factors. This study examined the expression of terminal galactose and sialic acid (SA) on serum IgA oligosaccharides in patients with IgA myeloma, compared to healthy control sera.

Methods Serum samples from 15 IgA myeloma patients and pooled serum from 100 healthy donors were analyzed. IgA was purified using peptide M affinity chromatography. Terminal galactose and SA expression on isolated IgA was analyzed by Ricinus communis agglutinin I and Sambucus nigra agglutinin lectin blotting.

Results IgA-heavy chains from both healthy individuals and all myeloma patients expressed galactose. SA was present in healthy control and in 14 out of 15 myeloma patients. Compared to controls, myeloma IgA showed 12–63% a reduction in galactose and a 67–97% reduction in SA expression on heavy chains. Notable galactosylation of IgA-light chains was observed in only three, while weak SA expression was seen in 14 myeloma cases. Healthy IgA was predominantly monomeric and expressed both galactose and SA. Myeloma IgA existed in both and polymeric forms expressing detectable galactose level, though with different expression levels among individuals. At the same time, SA was undetectable.

Conclusion The results of this study showed altered glycosylation of myeloma IgA. Compared to healthy control, myeloma IgA-heavy chains expressed reduced terminal galactose and SA. Notable galactosylation of light chains was observed in three cases. Unlike SA, galactose was detectable on intact monomeric and polymeric multiple myeloma IgA.

Keywords: multiple myeloma; IgA; glycosylation; sialic acid; galactose