Trauma remains the main cause of death for both civilians and those in uniform.
Trauma-associated coagulopathy is a complex process involving
inflammation, coagulation, and platelet dysfunction. It is unknown whether activation of
complement, which occurs invariably in
trauma patients, is involved in the expression of
trauma-associated coagulopathy. We designed a prospective study in which we enrolled 40
trauma patients and 30 healthy donors upon arrival to the emergency department of BIDMC. Platelets from healthy individuals were incubated with sera from
trauma patients and their responsiveness to a
thrombin receptor-activating peptide was measured using aggregometry.
Complement deposition on platelets from
trauma patients was measured by flow cytometry. Normal platelets displayed hypoactivity after incubation with
trauma sera even though exposure to
trauma sera resulted in increased agonist-induced
calcium flux. Depletion of
complement from sera further blocked activation of hypoactive platelets. Conversely, complement activation increased aggregation of platelets. Platelets from
trauma patients were found to have significantly higher amounts of C3a and C4d on their surface compared with platelets from controls. Depletion of
complement (C4d, C3a) reversed the ability of
trauma sera to augment agonist-induced
calcium flux in donor platelets. Our data indicate that
complement enhances platelet aggregation. Despite its
complement content,
trauma sera render platelets hypoactive and
complement depletion further blocks activation of hypoactive platelets. The defect in platelet activation induced by
trauma sera is distal to receptor activation since agonist-induced Ca2+ flux is elevated in the presence of
trauma sera owing to
complement deposition.