Quantitative measurement of carbohydrate binding activity of mouse macrophage lectin

A simple ELISA assay measuring lectin activity of a mouse macrophage galactose/N-acetylgalactosamine-specific C-type lectin (MMGL) was developed. The binding of galactosylated poly-lysine (termed a ligand) to the immobilized soluble form of MMGL (rML) was measured quantitatively. Consistent with the characteristics of MMGL, the binding was calcium dependent and inhibited by galactose and N-acetylgalactosamine. An antiserum against rML inhibited the ligand binding, demonstrating the usefulness of this method for the screening of blocking antibodies. Using this assay, we found a significant interaction between MMGL and carrageenans, a group of sulfated polygalactans. The inhibitory effect of carrageenans was not attributable to a nonspecific interaction because other types of sulfated polysaccharides, such as glycosaminoglycans and fucoidin, did not interfere with the ligand binding. The relevance of the present finding to the biological activities of carrageenans is discussed.