C5a-mediated neutrophil dysfunction is RhoA-dependent and predicts infection in critically ill patients

Area of Science:

• Immunology
• Critical Care Medicine
• Molecular Biology

Background:

• Critically ill patients face a high risk of nosocomial infections.
• The anaphylatoxin C5a is known to impair neutrophil phagocytosis, but the precise mechanisms and clinical relevance are unclear.

Purpose of the Study:

• To elucidate how C5a inhibits phagocytosis in neutrophils.
• To investigate the link between C5a-mediated neutrophil dysfunction and nosocomial infection acquisition in critically ill patients.

Main Methods:

• In vitro studies on healthy human neutrophils and neutrophils from critically ill patients.
• Analysis of RhoA activation, actin polymerization, and CD88 expression.
• Clinical cohort study of 60 critically ill patients to assess infection risk.

Main Results:

• C5a inhibited neutrophil RhoA activation and phagocytosis via PI3Kδ in healthy neutrophils, effects reversible by GM-CSF.
• Neutrophils from critically ill patients showed similar C5a-mediated dysfunction, also reversed by GM-CSF.
• C5a-mediated neutrophil dysfunction predicted nosocomial infection acquisition in critically ill patients (RR 5.8, HR 5.0).

Conclusions:

• C5a impairs neutrophil function in critical illness by inhibiting RhoA activation.
• GM-CSF can reverse C5a-induced neutrophil dysfunction.
• C5a-mediated neutrophil dysfunction is a significant predictor of nosocomial infections in critically ill patients, suggesting therapeutic targets.