Blood coagulation: a powerful bactericidal mechanism of human innate immunity.

Infection proliferates and disseminates rapidly and so innate immunity should react effectively and fast. Innate immunity mechanisms depend upon fluid dynamics and are different in compartments with slow (the tissues) and rapid (the bloodstream) liquid flow. In the tissues, coagulation initiated by clotting factors, platelets and erythrocytes, is prompt and effective mechanism of the first line of antibacterial defense. Resident macrophages, transmigrated neutrophils, monocytes, NETs and platelets are the second line of the defense. In the bloodstream the first line of innate immunity defense are erythrocytes that kill pathogens by oxygen, released from oxyhemoglobin (oxycytosis); the second line of the defense is coagulation that in case of overactivation may cause disseminated intravascular coagulation (DIC). Blood coagulation is the fastest mechanism of infection confinement and inactivation. It is the first and the last line of innate immunity defense and occurs both in the tissues and the bloodstream.