A peptide (P2) derived from the variable heavy chain of an anti-P-selectin monoclonal antibody (LYP20) inhibits leucocyte adhesion to thrombin-activated platelets and endothelial cells.

P-selectin, a member of the selectin family of adhesion molecules, is present in endothelial Weibel-Palade bodies and platelet alpha-granules, and is rapidly expressed on their surface upon activation, resulting in leucocyte adhesion. LYP20 is a functional monoclonal antibody previously generated in our laboratory that binds with high affinity and specificity directed against P-selectin. This binding is largely imparted by the specific sequence of amino acids present on the hypervariable portions of the IgG chains. We now show that a peptide derived from the heavy chain of mAb LYP20 dose dependently inhibits the adhesion of poly morphonuclear cells to resting and thrombin-activated endothelial cells (EC) and platelets. The scrambled form of this peptide, identical in amino acid composition to the authentic peptide but with altered sequence, was not inhibitory at corresponding concentrations. Binding studies revealed that this peptide also dose dependently bound to both resting and thrombin-activated EC and platelets. Our results may prove useful for the development of new therapeutic inhibitors to modulate leucocyte interactions in inflammatory disorders.