Dextran-binding human plasma antibody recognizes bacterial and yeast antigens and is inhibited by glucose...

Dextran-binding antibody was isolated in high yield from plasma of all 40 blood donors screened in a South Indian population. The antibody was purified by a single step affinity chromatography on Sephadex G100 using 1-O-methyl alpha-D-glucoside as eluant. Analysis of protein peaks obtained in size exclusion high pressure liquid chromatography (HPLC) revealed dominance of IgG and suggested the presence of polymeric IgA in this antibody. Methyl and para-nitrophenyl alpha-D-glucosides, in contrast to their beta-anomers, were very efficient inhibitors of binding of this antibody to dextran. Galactose and glucose were equally good inhibitors. Among disaccharide inhibitors sucrose was more efficient than maltose or melibiose. Hemoglobin artificially glycosylated to contain covalently-linked glucose or alpha-anomeric galactose was sugar-specifically recognized by this antibody. Galactose moieties in glycoproteins or polysaccharides were, however, not recognized. The dextran-binding antibody bound sugar-specifically to glycoconjugates from yeast (Saccharomyces cerevisiae) and to lipopolysaccharides from Klebsiella and group A Streptococci, but not to lipopolysaccharides from E. coli. Inhibition studies suggested glucose moiety with unsubstituted C2 and C4 and alpha-anomeric C1 as ideal for recognition by the dextran-binding antibody. Concentration of glucose required for 50% inhibition of binding of the purified antibody to polystyrene-coated dextran in phosphate buffered saline was above the glucose concentrations in normal sera, but well below those reached in diabetic sera. Binding of the antibody from dialysed plasma to immobilized dextran was lowered only marginally in presence of glucose at 4.5mM (which nears normal serum glucose concentrations), but substantially in presence of the sugar at 20mM and above which are reached in diabetic sera. If verified in vivo, inhibition of this antibody by high serum glucose may possibly be among reasons for the increased susceptibility of diabetics to infection.