Background:　Endothelial　hyperpermeability-induced　vascular　dysfunction　is　a　prevalent　and　significant　characteristic　in　critical　illnesses　such　as　sepsis　and　other　conditions　marked　by　acute　systemic　inflammation.　Platelet　endothelial　cell　adhesion　molecule-1　(PECAM-1)　and　Tie2　serve　as　transmembrane　receptors　within　endothelial　cells　(ECs),　playing　pivotal　roles　not　only　in　maintaining　EC-EC　junctions　but　also　in　influencing　vasculogenesis,　vessel　homeostasis,　and　vascular　remodeling.　Objectives:　At　present,　the　molecular　basis　of　the　PECAM-1-Tie2　interaction　remains　inadequately　elucidated.　In　the　study,　recombinant　soluble　PECAM-1　(sPECAM-1)　and　Tie2　(sTie2)　were　expressed　by　Drosophila　S2　and　HEK293　expression　systems,　respectively.　The　interactions　between　sPECAM-1　and　sTie2　were　investigated　using　the　Surface　Plasmon　Resonance　(SPR)　and　size-exclusion　chromatography　methods.　An　immunofluorescence　assay　was　used　to　detect　the　binding　of　sPECAM-1　and　sTie2　on　endothelial　cells.　Results:　PECAM-1　was　found　to　bind　with　sTie2　in　a　sodium　and　pH-dependent　manner　as　confirmed　by　the　ELISA,　the　D5-D6　domains　of　PECAM-1　might　play　a　crucial　role　in　binding　with　sTie2.　Surface　Plasmon　Resonance　(SPR)　results　showed　that　the　full　length　of　sPECAM-1　has　the　strongest　binding　affinity　(KD　=　48.4　nM)　with　sTie2,　compared　to　sPECAM-1-D1-D4　and　sPECAM-1-D1-D2.　This　result　is　consistent　with　that　in　the　ELISA.　In　addition,　size-exclusion　chromatography　demonstrated　that　sPECAM-1,　sTie2,　and　Ang1　can　form　a　ternary　complex.　Conclusion:　In　this　study,　we　determined　that　sPECAM-1　binds　to　sTie2　in　a　pH　and　sodium-dependent　manner.　The　full　length　of　sPECAM-1　has　the　strongest　binding　affinity,　and　the　D5-D6　domains　in　sPECAM-1　play　a　crucial　role　in　the　interaction　between　sPECAM-1　and　sTie2.