P-SELECTIN GLYCOPROTEIN LIGAND-1 MEDIATES ROLLING OF MOUSE BONE-MARROW-DERIVED MAST-CELLS ON P-SELECTIN BUT NOT EFFICIENTLY ON E-SELECTIN

It has been shown recently that mast cells play an essential role as a source of tumor necrosis factor-alpha production during neutrophil re cruitment to sites of bacterial infection. Increased numbers of mast c ells are indeed noted at sites of wound healing and inflammation. Thes e cells are either recruited from the bone marrow or proliferate local ly under cytokine stimulation. Little is known about how mast cell pro genitors extravasate into tissue. Using antibody-like fusion proteins of mouse E-selectin and P-selectin, we have analyzed the ability of im mature mouse bone marrow-derived mast cells (BMMC) to interact with th e endothelial selectins. The P-selectin glycoprotein ligand-1 (PSGL-1) was affinity-isolated from detergent extracts of surface biotinylated BMMC with both selectin-IgG fusion proteins. However, only P-selectin -IgG, but not E-selectin-IgG showed significant interaction with intac t BMMC as tested by flow cytometry and cell attachment assays with the immobilized fusion proteins under flow and non-flow conditions at phy siological shear stress. Thus, in spite of carrying the necessary carb ohydrate modifications which enable solubilized PSGL-1 to bind avidly to E-selectin, PSGL-1 on the surface of BMMC is presented in a way tha t prevents it from interacting efficiently with E-selectin. Affinity-p urified rabbit antibodies against mouse PSGL-1 almost completely block ed the interaction of BMMC with P-selectin-IgG in flow cytometry as we ll as in cell adhesion assays under static and under flow conditions. Our data reveal that PSGL-1 is the major binding site for P-selectin o n mouse BMMC progenitors, but does not support efficient interactions with E-selectin.