Partial dependence of human peripheral blood leukocyte binding to high molecular weight fucoidan on divalent cations

L-selectin (CD62L) is the principal leukocyte adhesion molecule for the high endothelial venules of peripheral lymph nodes. This adhesion has an absolute requirement for calcium ions. Nevertheless, some studies have shown carbohydrate adhesion receptor interactions on lymphocytes and neutrophils, including the L-selectin molecule, that are Ca-independent. In the present study fucoidan, a reportedly Ca2+ independent ligand of L-selectin, and Mabs to human CD62L were coupled to magnetic polystyrene beads (MPB), as a model of leukocyte-surface interactions, and the efficiency of human leukocyte separation was investigated. 30% of Ficoll-purified human mononuclear cells and 75% of dextran-purified human leukocytes (DPHL) were specifically bound by fucoidan-modified MPB in the presence of Ca2+; 55% of dextran-purified leukocytes were specifically bound in the absence of Ca2+. The specific binding was inhibited by an excess of free fucoidan. The data obtained show the presence of Ca-independent adhesion determinants, specific to fucoidan on human leukocytes. No significant specific binding of leukocytes to fucoidan-modified MPB was found after the incubation with fresh human Ca(2+)-depleted whole blood. More than 90% of DPHL were specifically bound to MPB modified with Mabs to human CD62L irrespective of Ca2+ presence. The same degree of separation was achieved after the incubation with fresh human Ca(2+)-depleted-whole blood with anti-CD62L modified beads.