Selectins and their ligands are required for leukocyte extravasation during inflammation. In the initial phase of the process, neutrophils (PMNs) first tether to and roll on P- and E-selectin expressed on activated endothelial cells via interacting with P-selectin glycoprotein ligand-1 (PSGL-1) for P-selectin and with PSGL-1, CD44, or E-selectin ligand-1 for E-selectin. Although the leukocyte–endothelial cell interactions have been extensively investigated, the dynamic contributions of the two selectin (P- and E-selectin) in mediating neutrophil transmigration is not clear.
To examine the potential involvement of these adhesion molecules in PMN transmigration, HUVEC is treated with LPS for 4 and 12 hours to get different selectin and ICAM-1 expression. P- or E-selectin expression of LPS-treated HUVECs is peaked by 4–5 h and return to baseline within 8–12 h. Preliminary data shows that PMN transmigration is significantly higher and faster in 4h-LPS stimulated HUVEC than those 12h-LPS treatment. Treatment with blocking and activating antibodies to the β2 integrins shows that high affinity LFA-1 binding to ICAM-1 is primarily responsible for mediating PMN transmigration across HUVEC. Using soluble E- or P-selectin competitively binding to their respective ligands indicates that P-selectin engaging PSGL-1 to activate LFA-1 manipulates PMN transmigration at the first 15 minutes, while E-selectin engaging PSGL-1 to activate LFA-1 only influences PMN transmigration after 15 minutes. These results give direct evidences of the distinct and dynamic contributions of P- and E-selectin in mediating neutrophils transmigration, and will provide new mechanistic insights into neutrophils interacting with the vessel wall.