An apparatus for the extracorporeal treatment of blood comprising an extracorporeal blood circuit (2), a pump (6) configured to provide fluid displacement within the extracorporeal blood circuit, and a reaction chamber (8) connected to the extracorporeal blood circuit and configured to receive blood or plasma from the circuit and treat the blood or plasma. The reaction chamber comprises an protease enzyme immobilized to a support, in which the protease enzyme is specific for, and capable of irreversibly cleaving, a human C5a present in the blood or plasma, wherein the abundance of the human C5a in the treated blood or plasma is less than that in the untreated blood or plasma. The apparatus finds utility in the extracorporeal treatment of blood from patients with inflammatory conditions, especially auto-immune disease and sepsis.
