The Function of Toll-Like Receptor 4 Expressions on Human Platelet in Platelet Activation

Lipopolysaccsharide (LPS) is a principal outer membrane component of gram-negative bacteria. It initiates an inflammatory response to infection by activating Toll-like receptor-4 (TLR4) in host. Infection increases risk for hemostasis, thrombosis, DIC, and tissue repair. Platelet contributes to the inflammation process through respond to invading pathogens, membrane adhesion molecule (P-selectin) is one of the indexes to determine platelet activation. Experiment was designed to study whether TLR4 is expressed on human platelet, and what is the function of TLR4 in platelet activation induced with LPS. Platelet suspensions from 10 heath people were treated with LPS of different concentrations for 1 hour, which were 0mg/L(control),0.1mg/L,0.5mg/L,1mg/L and 5mg/L, respectively. The expressions of TLR4, P-select on platelets and PAI-1 in platelets were detected through flow cytometry (FCM) and western blot(WB) methods. ADP-induced platelet aggregation was measured by LG-PABER aggregometer. Compared with control, the expressions of TLR4,P-selectin on platelets and PAI-1 in platelets after treated with LPS of 0.5mg/L,1mg/L and 5mg/L were increased (P<0.05). positive correlation was observed between TLR4 and P-selectin on platelets, but between TLR4 and PAI-1 in platelets. LPS of all concentrations did not affected ADP-induced platelet aggregation. Therefore, it is evident that functional TLR4 is expressed on human platelet. TLR4 on platelet might be one of the important intermedia between platelet activation and LPS or bacteria, and contribute to the inflammatory process in host. It is also worthy to study whether LPS affect platelet aggregation induced by other inductors.