349 Contact Hypersensitivity is Impaired in the Absence of Tissue Factor- and Protease-Activated Receptor 2-Mediated Signaling

Protease-activated receptor 2 (PAR2) and tissue factor (TF) play pivotal roles in hemostasis and thrombosis. PAR2 is mainly activated by proteolytic cleavage of extracellular proteases including the binary complex of TF and factor VIIa. Although their interaction with the innate and adaptive immune system has not yet been understood in detail, there is strong evidence that PAR2- and TF-mediated signaling exerts mandatory functions in cutaneous inflammation. In the current study, we have explored the role of PAR2- and TF-mediated signaling in murine contact hypersensitivity (CHS), a Tc1 CD8+ T cell immune response mimicking human allergic contact dermatitis. Therefore, a PAR2 receptor mutant mouse was generated in which PAR2 is insensitive to proteolytic activation, whereas thrombin-induced PAR1-mediated PAR2-transactivation still occurs. In a further approach, functional active TF was blocked in vivo by an anti-TF antibody. The CHS reaction, induced by epicutaneous sensitization and challenge with the hapten 2,4,6-trinitrochlorobenzene (TNCB), was significantly reduced in the PAR2 receptor mutant mice and in anti-TF-antibody treated animals. These results were demonstrated by an impaired cutaneous inflammatory response, assessed by a decreased ear swelling in vivo and a reduced cellular infiltrate of the skin measured by flow cytometric analysis and histology. In addition, the hapten-specific Tc1-mediated T cell response was attenuated as shown by a reduced T cell proliferation and a diminished Tc1-cytokine production after hapten-specific restimulation in vitro in PAR2 receptor mutant animals and after TF blockade. In summary, PAR2- and TF-regulated signaling significantly impairs the hapten-specific Tc1-mediated CHS reaction. In addition to their function in coagulation, our data suggest that PAR2 and TF also contribute to the immunoregulation of cutaneous inflammatory disorders.