Human Endothelial-Cell Specific Molecule-1 Binds Directly to the Integrin CD11a/CD18 (LFA-1) and Blocks Binding to Intercellular Adhesion Molecule-1

摘要

ICAMs are ligands for LFA-1,a major integrin of mononuclear cells involved in the immune and inflammatory processes.We previously showed that endothelial cell specific molecule-1 (ESM-1) is a proteoglycan secreted by endothelial cells under the control of inflammatory cytokines.Here,we demonstrate that ESM-1 binds directly to LFA-1 onto the cell surface of human blood lymphocytes,monocytes,and Jurkat cells.The binding of ESM-1 was equally dependent on Ca~(2+),Mg~(2+),or Mn~(2+) divalent ions,which are specific,saturable,and sensitive to temperature.An anti-CD11a mAb or PMA induced a transient increase in binding,peaking 5 min after activation.Direct binding of ESM-1 to LFA-1 integrin was demonstrated by specific coimmunoprecipitation by CD11a and CD18 mAbs.A cell-free system using a Biacore biosensor confirmed that ESM-1 and LFA-1 dynamically interacted in real time with high affinity (K_d=18.7nM).ESM-1 consistently inhibited the specific binding of soluble ICAM-1 to Jurkat cells in a dose-dependent manner.These results suggest that ESM-1 and ICAM-1 on binding sites very close to but distinct from the I domain of CD11a.Through this mechanism,ESM-1 could be implicated in the regulation of the LFA-1/ICAM-1 pathway and may therefore influence both the recruitment of circulating lymphocytes to inflammatory sites and LFA-1-dependent leukocyte adhesion and activation