Production of acute pulmonary injury by leukocytes and activated complement

The adult respiratory distress syndrome (ARDS) frequently occurs after sepsis and major trauma. Since both sepsis and trauma may cause activation of the complement system, we have infused rabbits with complement-activated plasma (AP) and have studied the effects on leukocyte counts, respiratory rate, PaO₂, and lung morphology, Sustained AP infusion caused: (1) early granulocytopenia, (2) progressive hypoxemia and tachypnea, and (3) pulmonary vascular plugging by aggregates of degenerating granulocytes with interstitial edema and endothelial injury. These changes were not observed in control animals infused with unactivated plasma or in animals rendered leukopenic with nitrogen mustard. Complement activation in patients with sepsis arid trauma may be an etiologic factor in the development of ARDS.