Multiple Specificity of Human Serum Dextran-Binding Immunoglobulin: α (1→6)- and β (1→3)-linked Glucose and α (1→3)-linked Galactose in Natural Glycoconjugates are Recognized

Abstract

Dextran-binding immunoglobulin (DIg) was detected in circulating immune complexes in young healthy blood donors. High molecular weight dextran or non-dialysable polysaccharides of edible sugar added to serum markedly increased DIg-containing immune complexes. DIg from plasma was purified by an improved affinity chromatography using Sephadex G-200 to increase yield. Recognition by DIg of α (1→6) glucans in polystyrene-coated dextran was inhibited totally and its less avid recognition of β (1→3) glucans in yeast and barley partially by 50 mM 1-O-methyl-α-D-glucoside. All fractions of non-dialysable edible sugar separated by electrophoresis were recognized by DIg. While purified DIg contained nearly equal amounts of IgM and IgG, DIg in immune complexes isolated after addition of dextran to serum was 72% IgM. Recognition of bovine thyroglobulin, tumour laminin, and peanut-agglutinin-binding bovine heart glycoproteins, all containing terminal α (1→3)-linked galactose epitopes, by DIg was inhibitable by 1-O-methyl-α-D-glucoside. Enzymatic removal or modification of the respective terminal α (1→3)-linked galactose groups in these glycoproteins abolished their recognition by the antibody. Results suggest that DIg recognizes α (1→6) glucans, α (1→3) - linked galactose epitopes and less avidly β (1→3) glucans. Results also point to a new immunomodulatory effect of non-dialysable sugar and dietary β-glucans.

Keywords:

• Dextran-binding serum immunoglobulin (DIg)
• terminal α-D-galactoside
• non-dialysable sugar
• β-glucans
• multiple specificity