FIGURE 3.

(a) The multistep process of leucocyte recruitment requires interaction of membrane-bound macromolecules near the surface of the leucocyte and the endothelium.⁶⁷ The adhesion molecules extend only tens of nm from the cell surface. The common cartoon of this cascade does not take into account the presence of a thick endothelial surface layer which limits access to the cell surface receptors. (b) Leucocytes (arrows) in frog mesentery vessels preferentially localize to endothelial cell borders as revealed by silver staining.²⁷ (a) Courtesy of Professor Scott I. Simon and (b) used with permission of the American Physiological Society.