MONOCYTES AND TISSUE FACTOR PROMOTE THROMBOSIS IN A MURINE MODEL OF OXYGEN DEPRIVATION

Clinical conditions associated with local or systemic hyperemia can le ad to prothrombotic diatheses, This study was undertaken to establish a model of whole-animal hypoxia wherein oxygen deprivation by itself w ould be sufficient to trigger tissue thrombosis. Furthermore, this mod el was used to test the hypothesis that hypoxia-induced mononuclear ph agocyte (MP) recruitment and tissue factor (TF) expression may trigger the local deposition of fibrin which occurs in response to oxygen dep rivation. Using an environmental chamber in which inhaled oxygen tensi on was lowered to 6%, hypoxic induction of thrombosis was demonstrated in murine pulmonary vasculature by 8 h based upon: (a) immunohistolog ic evidence of fibrin formation in hypoxic lung tissue using an antifi brin antibody, confirmed by 22.5-nm strand periodicity by electron mic roscopy; (b) immunoblots revealing fibrin gamma-gamma chain dimers in lungs from hypoxic but not normoxic mice or hypoxic mice treated with hirudin; (c) accelerated deposition of I-125-fibrin/fibrinogen and In- 111-labeled platelets in the lung tissue of hypoxic compared with norm oxic animals; (d) reduction of tissue I-125-fibrin/ fibrinogen accumul ation in animals which had either been treated with hirudin or deplete d of platelets before hypoxic exposure, Because immunohistochemical an alysis of hypoxic pulmonary tissue revealed strong MP staining for TF, confirmed by increased TF RNA in hypoxic lungs, and because In-111-la beled murine MPs accumulated in hypoxic pulmonary tissue, we evaluated whether recruited MPs might be responsible for initiation of hypoxia- induced thrombosis, This hypothesis was supported by several lines of evidence: (a) MP depletion before hypoxia reduced thrombosis, as measu red by reduced I-125-fibrin/fibrinogen deposition and reduced accumula tion of cross-linked fibrin by immunoblot; (b) isolated murine MPs dem onstrated increased TF immunostaining when exposed to hypoxia; and (c) administration of an anti-rabbit TF antibody that crossreacts with mu rine TF decreased I-125-fibrin/fibrinogen accumulation and cross-linke d fibrin accumulation in response to hypoxia in vivo, In summary, thes e studies using a novel in vivo model suggest that MP accumulation and TF expression may promote hypoxia-induced thrombosis.