FUNCTIONAL AND STRUCTURAL CHARACTERIZATION OF THE EOSINOPHIL P-SELECTIN LIGAND

Our recent studies have indicated an important role for P-selectin in eosinophil adhesion, We have therefore compared eosinophil and neutrop hil binding with nasal polyp endothelium as well as purified P-selecti n. We have also compared the structure and expression of the eosinophi l and neutrophil P-selectin ligands. Using the frozen section assay, e osinophils bound to 2-fold more blood vessels within the nasal polyp t issue than neutrophils. Up to 10-fold more eosinophils than neutrophil s bound per unit length of endothelium, Neutrophil and eosinophil bind ing was inhibited by a mAb against P-selectin and a P-selectin chimera which binds to the P-selectin ligand. Eosinophils bound with approxim ately 2-fold greater avidity to purified P-selectin under now conditio ns, Using SDS-PAGE we characterized the eosinophil P-selectin ligand a s a sialylated, homodimeric glycoprotein consistent with the known str ucture of PSGL-1. However, expression of PSGL-1 by eosinophils was sig nificantly greater than on neutrophils. The eosinophil ligand had a ca lculated molecular mass by SDS-PACE of approximately 10 kDa greater th an the neutrophil ligand, which was not due to differences in N-glycos ylation. Eosinophils expressed the 15-decapeptide repeat form of PSGL- 1 compared with neutrophils that have the 16-decapeptide repeat form, The increased binding of eosinophils, compared with neutrophils, to P- selectin in both an ex-vivo and in vitro assay suggests that P-selecti n may have a role directing the specific migration of eosinophils in d iseases such as asthma. The increased avidity may be due to increased expression of PSGL-1 by eosinophils, differences in the peptide backbo ne, or post-translational modifications.