When complement activation products were individually implicated in trauma-induced local and systemic trauma complications, several groups found that early C3a generation and depletion of C3 with a resultant increase in the C3a/C3 ratio were associated with the development of acute lung injury, ARDS, sepsis, multiple organ dysfunction and consequently a poor prognosis (6, 9–12). This evidence concerns the gene C3 and acute respiratory distress syndrome.