P-selectin glycoprotein ligand 1 (PSGL-1) is a physiological ligand for E-selectin in mediating T helper 1 lymphocyte migration

P-selectin glycoprotein ligand 1 (PSGL-1) is a sialomucin expressed on leuk ocytes that mediates neutrophil rolling on the vascular endothelium. Here, the role of PSGL-1 in mediating lymphocyte migration was studied using mice lacking PSGL-1. In a contact hypersensitivity model, the infiltration of C D4(+) T lymphocytes into the inflamed skin was reduced in PSGL-1-deficient mice. In vitro-generated T helper (Th)1 cells from PSGL-1-deficient mice di d not bind to P-selectin and migrated less efficiently into the inflamed sk in than wild-type Th1 cells. To assess the role of PSGL-1 in P- or E-select in-mediated migration of Th1 cells, the cells were injected into E- or P-se lectin-deficient mice. PSGL-1-deficient Th1 cells did not migrate into the inflamed skin of E-selectin-deficient mice, indicating that PSGL-1 on Th1 c ells is the sole ligand for P-selectin in vivo. In contrast, PSGL-1-deficie nt Th1 cells migrated into the inflamed skin of P-selectin-deficient mice, although less efficiently than wild-type Th1 cells. This E-selectin-mediate d migration of PSGL-1-deficient or wild-type Th1 cells was not altered by i njecting a blocking antibody to L-selectin. These data provide evidence tha t PSGL-1 on Th1 cells functions as one of the E-selectin ligands in vivo.