Adhesion of leukocytes to endothelium: roles of divalent cations, surface charge, chemotactic agents and substrate.

The attachment of polymorphonuclear leukocytes (PMN) to the endothelial lining of blood vessels is an important initial event in the acute inflammatory reaction. Experiments were carried out to examine some of the parameters of this adhesive interaction and the extent to which the substrate (endothelium) plays a role in controlling the process. Using a monolayer collection assay for adhesion, we found a requirement for divalent cations. Mn2+ produces maximal adhesion followed by Zn2+ greater than Ni2+ greater than Mg2+ greater than Ba2+ greater than Ca2+. Pretreatment of either the endothelium of PMN with chemotactic agents (zymosan-activated serum, a bacterial filtrate, C5a and formyl-methionyl-leucyl-phenylalanine) causes an increase in the attachment of PMN to endothelial monolayers. Modulations of net surface charge, as measured by laser Doppler electrophoresis, are not correlated to alterations in adhesion. Mn2+, which produces maximal adhesion, reduces the net surface charge to the same extent as Ca2+, which has the smallest effect on adhesion. Similarly, reductions in net surface charge are not responsible for the increases in adhesion due to the chemotactic agents because there are no differences in electrophoretic mobilities between cells treated with either chemotactic agents or their appropriate controls. Scatchard analysis of the binding of the chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, indicates the presence of high-affinity binding sites on the surface of the endothelium. The results suggest a role for the endothelium in mediating the adhesive interaction with the PMN.