Binding of function-blocking mAbs to mouse and human P-selectin glycoprotein ligand-1 peptides with and without tyrosine sulfation

P‐selectin glycoprotein ligand‐1 (PSGL‐1) mediates rolling of leukocytes on P‐selectin‐expressing endothelial cells under shear flow. Function‐blocking monoclonal antibodies (mAbs) against mouse and human PSGL‐1 recognize an anionic segment at the N‐terminus of PSGL‐1. High affinity interaction of PSGL‐1 with P‐selectin requires sulfation of tyrosines 46, 48, and 51 (human) or 54 and 56 (mouse). We tested binding of two anti‐human (KPL1 and PL1) and two anti‐mouse (4RA10 and 2PH1) PSGL‐1 mAbs to synthetic peptides of N‐terminus of human and mouse PSGL‐1 and found binding to be independent of tyrosine sulfation. In peptide‐blocking experiments, sulfated and nonsulfated human and mouse peptides competed with antibody binding to PSGL‐1 expressed on myeloid cells. Arylsulfatase treatment significantly reduced P‐selectin binding but had no effect on antibody binding. Our data show, in three independent assay systems, that function‐blocking antibodies to mouse or human PSGL‐1 do not require sulfation of N‐terminal tyrosines for binding.