The plasma contact system as a modulator of innate immunityWu, YiCurrent Opinion in Hematology: September 2018 - Volume 25 - Issue 5 - p 389–394 doi: 10.1097/MOH.0000000000000448 HEMOSTASIS AND THROMBOSIS: Edited by Alvin H. Schmaier Abstract Author Information Purpose of review The contact system is a plasma protease cascade, which activates the proinflammatory kallikrein–kinin system and the procoagulant intrinsic coagulation pathway. Recent advances demonstrating the novel functions of this system as a key player of innate immune system will be introduced in the present review. Recent findings The role of the contact system is to initiate and participate in pathophysiological responses to injury, mainly the processes of coagulation and inflammation. The past few years have seen substantial progress, showing a new role of this system in regulation of innate immunity. The relationship between high-molecular-weight kininogen and lipopolysaccharide (LPS) has been investigated and a new function of high-molecular-weight kininogen has been identified as the critical LPS carrier supporting endotoxemia. In contrast, the role of high-molecular-weight kininogen in Klebsiella pneumoniae sepsis is limited. Coagulation factor XII (FXII) plays a detrimental role in murine wound healing and host defense against K. pneumoniae sepsis. In the pathogenesis of arthritis and colitis, the activation of plasma kallikrein and downstream cleavage of high-molecular-weight kininogen and release of bradykinin constitutes a critical pathway in the innate immune mechanism, whereas FXII is not important. Summary Current findings indicate that the plasma contact system functions as an important constituent of innate immune system, contributing to the pathogenesis of the immunological and infectious diseases. The Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania, USA Correspondence to Yi Wu, The Sol Sherry Thrombosis Research Center, Temple University School of Medicine, 3420 North. Broad Street, Philadelphia, PA 19140, USA. Tel: +1 215 707 4423; fax: +1 215 707 2783; e-mail: email@example.com Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.