Endogenous α2-antiplasmin is protective during severe gram-negative sepsis (melioidosis)

α2-Antiplasmin (A2AP) is a major inhibitor of fibrinolysis by virtue of its capacity to inhibit plasmin. Although the fibrinolytic system is strongly affected by infection, the functional role of A2AP in the host response to sepsis is unknown. To study the role of A2AP in melioidosis, a common form of community-acquired sepsis in Southeast Asia and Northern Australia caused by the gram-negative bacterium Burkholderia pseudomallei. In a single-center observational study A2AP was measured in patients with culture-proven septic melioidosis. Wild-type and A2AP-deficient (A2AP(-/-)) mice were intranasally infected with B. pseudomallei to induce severe pneumosepsis (melioidosis). Parameters of inflammation and coagulation were measured, and survival studies were performed. Patients with melioidosis showed elevated A2AP plasma levels. Likewise, A2AP levels in plasma and lung homogenates were elevated in mice infected with B. pseudomallei. A2AP-deficient (A2AP(-/-)) mice had a strongly disturbed host response during experimental melioidosis as reflected by enhanced bacterial growth at the primary site of infection accompanied by increased dissemination to distant organs. In addition, A2AP(-/-) mice showed more severe lung pathology and injury together with an increased accumulation of neutrophils and higher cytokine levels in lung tissue. A2AP deficiency further was associated with exaggerated systemic inflammation and coagulation, increased distant organ injury, and enhanced lethality. This study is the first to identify A2AP as a protective mediator during gram-negative (pneumo)sepsis by limiting bacterial growth, inflammation, tissue injury, and coagulation