Celladhesionisafundamentalfeatureofmulticellularorganismsincludingtheirdefensemechanisms.Inthelatercaseinmammals,leukocytesplaycentralrole.Theybindbacteria,parasites,viruses,tumorcellsetc.FurThermore,theirinteractionswiththeendotheliumareofspecialimportance.Duringaninflammationorimmunereaction,specializedleukocytes(eosinophilicgranulocytes)adheretoandpassthroughtheendotheliumofthebloodvesselsandtheunderlyingmatrix.Thereactionpassesthroughthefollowingsteps:1.Rolling(theflowofcellsissloweddownbyfirstmakingcontactstotheendotheliumviaP-,E-,andL-selectinsandtheirreceptors);2.Adhesion(Afteractivationofleukocyteintegrins,firmcontactsareestablishedbetweenthemandendotheliummoleculesoftheIgsuperfamily-LFA-1,Mac-1,VLA-4etc.);3.Flatteningofthecellsanddiapedesis(Adheringleukocytescrawltoanintercellularjunctionoftheendotheliumandthentransmigratetooreventhroughtheintercellularmatrix.ThisismediatedbyahomophilicinteractionsofPECAMandCD31. Contributor:KosiGramatikoff,PhD REFERENCES:DVestweberAndJEBlanks.MechanismsThatRegulatetheFunctionoftheSelectinsandTheirLigandsPhysiolRev,Jan1999;79:181-213.EFPlowetal.LigandBindingtoIntegrinsJ.Biol.Chem.,Jul2000;275:21785-21788.FSánchez-Madridetal.LeukocytepolarizationincellmigrationandimmuneinteractionsEMBOJ.,Feb1999;18:501-511.MAJutila.FunctionandregulationofleukocytehomingreceptorsJ.Leukoc.Biol.,Jan1994;55:133-140.TMCarlosandJMHarlan.Leukocyte-endothelialadhesionmoleculesBlood,Oct1994;84:2068-2101.