• S Denk, M Neher, R Wiegner, M Kalbitz, M Weiss, and M Huber-Lang.
• 1Department of Orthopedic Trauma, Hand, Plastic and Reconstruction Surgery, University Hospital Ulm, Germany 2Department of Anesthesiology, University Hospital Ulm, Germany.
• Shock. 2015 Oct 1;44 Suppl 2:18.

IntroductionDuring systemic inflammatory conditions, such as sepsis, the immune system is uniquely challenged. Studies indicate that excessive complement activation is associated with impaired neutrophil function although the mechanism is marginally characterised. As a balanced cytosolic pH regulation is essential for cellular function, the effect of complement activation on neutrophil pH and resulting functional changes was investigated.MethodsIsolated human neutrophils were incubated with C5a and analyzed for intracellular pHi by flow cytometry. For evaluation of sepsis-induced changes, neutrophil pHi was determined in experimental cecal-ligation and puncture- (CLP) induced murine sepsis and in patients with septic shock (ethical approval 163/2003). Results were analyzed using one-way ANOVA followed by Student Newman-Keuls-test.ResultsC5a significantly increased pHi in neutrophils in a dose- and time-dependent manner, whereas C3a failed to alter pHi. C5a was found to induce the sodium-hydrogen exchanger-1 (NHE-1) by C5a-receptor interaction with subsequent intracellular Ca2+ release and activation of PKC and calmodulin. This C5a-induced alkalinisation resulted in exocytosis of lactoferrin and myeloperoxidase from healthy human neutrophils and was almost normalised by inhibition of NHE-1. In vivo, CLP-induced sepsis also increased neutrophil pHi, which could be mitigated by pretreatment with a C5a-receptor antagonist. Similarly, pHi was significantly elevated in neutrophils from patients with sepsis (n = 10) compared to healthy volunteers (n = 10).ConclusionThese results suggest that excessive complement activation via C5a leads to a NHE-1-mediated shift of pHi and subsequent neutrophil functions during septic shock. Therefore, targeted inhibition of the C5a-C5aR interaction may balance the pHi homeostasis of neutrophils regulating crucial cellular functions during sepsis.

15 keywords...

hide…