Hexa-acylated LPS-lipid A deploys the appropriate level of fibrin to confer protection through MyD88

•Fibrin has been demonstrated to function protectively against pathogens in previous studies, but a very high level of fibrin played a negative role during some infections.•An appropriate fibrin level performs critical protective roles during defense against plague, revealing the “double-edged sword” characteristic of fibrin during infections.•We demonstrated that the appropriate level of fibrin formation was deployed by hexa-acylated LPS-lipid A through myeloid differentiation factor 88.

SummaryObjectivesFibrin has been demonstrated to function protectively against pathogens in our previous studies, but we observed that a very high level of fibrin played a negative role during infection. We performed this research to address the complication.MethodsAfter infection, mice were monitored daily and harvested on day 4. The fibrin levels within the tissue samples were quantified by Western-blot. The in situ assay was used to detect plasminogen activators, protein C-ase and prothrombinase activation. PT-PCR was used to test coagulation factors expression.ResultsMice treated with Coumadin showed that the protection correlates with fibrin levels. By interacting with Toll-like receptor 4, the hexa-acylated lipopolysaccharide, although not the tetra-acylated lipopolysaccharide, activates coagulation and regulates plasminogen activator inhibitor 1, thrombin activatable fibrinolysis inhibitor and thrombomodulin expression through myeloid differentiation factor 88, leading to plasminogen activators, protein C-ase and prothrombinase activation and fibrin formation. Because of the regulation, fibrin formation was controlled to deposit appropriate levels and confer protection.ConclusionsWe demonstrated that the appropriate level of fibrin formation was deployed by hexa-acylated LPS-lipid A through myeloid differentiation factor 88 to confer protection.