SELECTIVE INHIBITORY EFFECTS OF THE ANTICOAGULANT ACTIVATED PROTEIN-CON THE RESPONSES OF HUMAN MONONUCLEAR PHAGOCYTES TO LPS, IFN-GAMMA, OR PHORBOL ESTER

Recent studies have shown that infusion of the anticoagulant protein, activated protein C (APC), can ameliorate many of the systemic effects of endotoxemia in experimental animals, although the mechanisms in th is action are unknown. We investigated the effects of APC on the respo nses of blood monocytes, alveolar macrophages, and cells of the monocy te line, THP-1, to stimulation in vitro by LPS, IFN-gamma, or PMA. Mon onuclear phagocyte (MO) activation was associated with rapid productio n of TNF-alpha, down-regulation of the glycophosphatidylinositol linke d protein CD14 (the key MO receptor for complexes of LPS and LPS-bindi ng protein responsible for intracellular signaling), and down-regulati on of the related LPS-binding proteins CD11b and CD18. Addition of APC , but not the zymogen, PC, or active site-blocked APC, inhibited selec ted MO responses involving the CD14-dependent LPS-induced pathway of M O activation, or activation induced by IFN-gamma or PMA. Thus, APC inh ibited the production of TNF-alpha and prevented down-regulation of me mbrane CD11b, CD14, and CD18, but had no effect on up-regulation of MH C class II, ICAM-1, or IL-2R, down-regulation of MO expression of anot her glycophosphatidylinositol-linked protein, CD59, or production of r eactive oxygen intermediates. These data show that APC inhibits host c ytokine production but maintains MO responses associated with adhesion , phagocytosis, and killing of Gram-negative bacteria, such that use o f APC may be a logical and potent adjunctive therapy in select inflamm atory diseases involving MO activation and damaging host cytokine over production.