Complement component 5 does not interfere with physiological 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 physiological and pathophysiological hemostasis has not, however, been fully elucidated. This study examined the effects of C5 in normal hemostasis and in Escherichia coli-induced coagulation and tissue factor (TF) up-regulation. Fresh whole blood obtained from six healthy donors and one C5-deficient individual (C5D) was anti-coagulated 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 TLR-4 inhibitor eritoran. C5D blood was reconstituted with purified human C5. TF mRNA was measured by quantitative polymerase chain reaction (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 enzyme-linked immunosorbent assay (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 TLR-4.

Systemic inflammation in acute intermittent porphyria: a case-control study

This study aimed to examine whether acute intermittent porphyria (AIP) is associated with systemic inflammation and whether the inflammation correlates with disease activity. A case-control study with 50 AIP cases and age-, sex- and place of residence-matched controls was performed. Plasma cytokines, insulin and C-peptide were analysed after an overnight fast using multiplex assay. Long pentraxin-3 (PTX3) and complement activation products (C3bc and TCC) were analysed using enzyme-linked immunosorbent assay (ELISA). Urine porphobilinogen ratio (U-PBG, µmol/mmol creatinine), haematological and biochemical tests were performed using routine methods. Questionnaires were used to register AIP symptoms, medication and other diseases. All 27 cytokines, chemokines and growth factors investigated were increased significantly in symptomatic AIP cases compared with controls (P < 0·0004). Hierarchical cluster analyses revealed a cluster with high visfatin levels and several highly expressed cytokines including interleukin (IL)-17, suggesting a T helper type 17 (Th17) inflammatory response in a group of AIP cases. C3bc (P = 0·002) and serum immunoglobulin (Ig)G levels (P = 0·03) were increased significantly in cases with AIP. The U-PBG ratio correlated positively with PTX3 (r = 0·38, P = 0·006), and with terminal complement complex (TCC) levels (r = 0·33, P = 0·02). PTX3 was a significant predictor of the biochemical disease activity marker U-PBG in AIP cases after adjustment for potential confounders in multiple linear regression analyses (P = 0·032). Prealbumin, C-peptide, insulin and kidney function were all decreased in the symptomatic AIP cases, but not in the asymptomatic cases. These results indicate that AIP is associated with systemic inflammation. Decreased C-peptide levels in symptomatic AIP cases indicate that reduced insulin release is associated with enhanced disease activity and reduced kidney function.

The key roles of complement and tissue factor in Escherichia coli-induced coagulation in human whole blood

The complement system and the Toll-like (TLR) co-receptor CD14 play important roles in innate immunity and sepsis. Tissue factor (TF) is a key initiating component in intravascular coagulation in sepsis, and long pentraxin 3 (PTX3) enhances the lipopolysaccharide (LPS)-induced transcription of TF. The aim of this study was to study the mechanism by which complement and CD14 affects LPS- and Escherichia coli (E. coli)-induced coagulation in human blood. Fresh whole blood was anti-coagulated with lepirudin, and incubated with ultra-purified LPS (100 ng/ml) or with E. coli (1 × 10(7) /ml). Inhibitors and controls included the C3 blocking peptide compstatin, an anti-CD14 F(ab')2 antibody and a control F(ab')2 . TF mRNA was measured using quantitative polymerase chain reaction (qPCR) and monocyte TF surface expression by flow cytometry. TF functional activity in plasma microparticles was measured using an amidolytic assay. Prothrombin fragment F 1+2 (PTF1.2) and PTX3 were measured by enzyme-linked immunosorbent assay (ELISA). The effect of TF was examined using an anti-TF blocking antibody. E. coli increased plasma PTF1.2 and PTX3 levels markedly. This increase was reduced by 84->99% with compstatin, 55-97% with anti-CD14 and > 99% with combined inhibition (P < 0·05 for all). The combined inhibition was significantly (P < 0·05) more efficient than compstatin and anti-CD14 alone. The LPS- and E. coli-induced TF mRNA levels, monocyte TF surface expression and TF functional activity were reduced by > 99% (P < 0·05) with combined C3 and CD14 inhibition. LPS- and E. coli-induced PTF1.2 was reduced by 76-81% (P < 0·05) with anti-TF antibody. LPS and E. coli activated the coagulation system by a complement- and CD14-dependent up-regulation of TF, leading subsequently to prothrombin activation.

C1-inhibitor efficiently inhibits Escherichia coli-induced tissue factor mRNA up-regulation, monocyte tissue factor expression and coagulation activation in human whole blood

Both the complement system and tissue factor (TF), a key initiating component of coagulation, are activated in sepsis, and cross-talk occurs between the complement and coagulation systems. C1-inhibitor (C1-INH) can act as a regulator in both systems. Our aim in this study was to examine this cross-talk by investigating the effects of C1-INH on Escherichia coli-induced haemostasis and inflammation. Fresh human whole blood collected in lepirudin was incubated with E. coli or ultrapurified E. coli lipopolysaccharide (LPS) in the absence or presence of C1-INH or protease-inactivated C1-INH. C3 activation was blocked by compstatin, a specific C3 convertase inhibitor. TF mRNA was measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and TF surface expression was measured by flow cytometry. In plasma, the terminal complement complex, prothrombin F1·2 (PTF1·2) and long pentraxin 3 (PTX3) were measured by enzyme-linked immunosorbent assay (ELISA). Cytokines were analysed using a multiplex kit. C1-INH (1·25-5 mg/ml) reduced both LPS- and E. coli-induced coagulation, measured as a reduction of PTF1·2 in plasma, efficiently and dose-dependently (P < 0·05). Both LPS and E. coli induced marked up-regulation of TF mRNA levels and surface expression on whole blood monocytes. This up-regulation was reduced efficiently by treatment with C1-INH (P < 0·05). C1-INH reduced the release of PTX3 (P < 0·05) and virtually all cytokines measured (P < 0·05). Complement activation was inhibited more efficiently with compstatin than with C1-INH. C1-INH inhibited most of the other readouts more efficiently, consistent with additional non-complement-dependent effects. These results indicate that complement plays a role in activating coagulation during sepsis and that C1-INH is a broad-spectrum attenuator of the inflammatory and haemostatic responses.