Coagulation Factor XII Is an Antibacterial Protein That Acts Against Bacterial Infection via Its Heavy Chain.

Coagulation factor XII (FXII), the initiator of the intrinsic coagulation pathway, is not involved in hemostasis but is associated with pathological thrombosis. Bacterial infections activate coagulation cascades, although the underlying mechanisms remain not fully understood. Here, we revealed that FXII exhibits antibacterial activity through its heavy chain (hFXII) against Pseudomonas aeruginosa (P. aeruginosa), a Gram-negative bacterium. We constructed an FXII-deficient (FXII(-/-)) mouse model and demonstrated that FXII plays a critical role in antibacterial functions. FXII and hFXII significantly reduced bacterial loads via intravenous injection, confirming their antibacterial activity in FXII(-/-). To further investigate the pathophysiological implications of FXII in the P. aeruginosa-induced disseminated intravascular coagulation (DIC) mouse model, FXII and hFXII effectively reduced DIC-related bacterial infections, alleviated organ damage, and decreased fibrin deposition, consequently improving survival rates. This study indicates that FXII exhibits both in vitro and in vivo antibacterial activity, primarily mediated through its heavy chain. In thrombotic diseases triggered by Gram-negative bacterial infections, the antibacterial functions of FXII may influence the progression of the disease. These results not only redefine the critical role of the intrinsic coagulation pathway in innate immune defense but also provide novel insights into the prevention and treatment of severe infection-related diseases.