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. 2018 Feb 26;9:312. doi: 10.3389/fimmu.2018.00312

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Copyright © 2018 Oehmcke-Hecht and Köhler.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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The human contact system. Assembly of contact system factors on foreign biological or artificial surfaces activates factor XII (FXII). FXIIa activates factor XI (FXI) that triggers the intrinsic pathway of coagulation, which is involved in thrombosis. FXII also activates plasma kallikrein (PK), which cleaves high molecular weight kininogen (HK), followed by the release of the pro-inflammatory peptide bradykinin and antimicrobial peptides (AMPs). FXII and PK contribute in vitro to complement activation.