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

Summary 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. C 1‐inhibitor ( C 1‐ 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 C 1‐ INH on E scherichia 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 C 1‐ INH or protease‐inactivated C 1‐ INH . C 3 activation was blocked by compstatin, a specific C 3 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 F 1·2 ( PTF 1·2) and long pentraxin 3 ( PTX 3) were measured by enzyme‐linked immunosorbent assay ( ELISA) . Cytokines were analysed using a multiplex kit. C 1‐ INH (1·25–5 mg/ml) reduced both LPS ‐ and E . coli ‐induced coagulation, measured as a reduction of PTF 1·2 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 C 1‐ INH ( P  < 0·05). C 1‐ INH reduced the release of PTX 3 ( P  < 0·05) and virtually all cytokines measured ( P  < 0·05). Complement activation was inhibited more efficiently with compstatin than with C 1‐ INH . C 1‐ 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 C 1‐ INH is a broad‐spectrum attenuator of the inflammatory and haemostatic responses.