Complement component 5 does not interfere with physiologic hemostasis but is essential for Escherichia coli-induced coagulation accompanied by Toll-like receptor 4.

There is a close cross-talk between complement, Toll-like receptors (TLRs) and coagulation. The role of the central complement component 5 (C5) in physiologic and pathophysiologic hemostasis has however not been fully elucidated. This study examined the effects of C5 in normal hemostasis and in Escherichia coli (E.coli)-induced coagulation and tissue factor (TF) upregulation. Fresh whole blood obtained from six healthy donors and one C5-deficient individual (C5D) was anticoagulated with the thrombin inhibitor lepirudin. Blood was incubated with or without E.coli in the presence of the C5 inhibitor eculizumab, a blocking anti-CD14 monoclonal antibody (anti-CD14) or the TLR4 inhibitor eritoran. C5D blood was reconstituted with purified human C5. TF mRNA was measured by qPCR, and monocyte TF and CD11b surface expression by flow cytometry. Prothrombin fragment 1+2 (PTF1·2) in plasma and microparticles exposing TF (TF-MP) was measured by ELISA. Coagulation kinetics were analyzed by rotational thromboelastometry and platelet function by PFA-200. Normal blood with eculizumab as well as C5D blood with or without reconstitution with C5 displayed completely normal biochemical hemostatic patterns. In contrast, E.coli-induced TF mRNA and TF-MP were significantly reduced by C5 inhibition. C5 inhibition combined with anti-CD14 or eritoran completely inhibited the E.coli-induced monocyte TF, TF-MP and plasma PTF1·2. Addition of C5a alone did not induce TF expression on monocytes. In conclusion, C5 showed no impact on physiological hemostasis, but substantially contributed to E.coli-induced procoagulant events, which were abolished by the combined inhibition of C5 and CD14 or TLR4. This article is protected by copyright. All rights reserved.