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* Clinical Immunology, Department of Medicine;
Department of Immunology; and Cardiology, Department of Medicine, Baylor College of Medicine, Department of Veterans Affairs, Houston, Texas 77030
To whom requests for reprints should be addressed at 1 Veterans Affairs Medical Center, 2002 Holcombe Boulevard, Building 109, Houston, TX 77030. E-mail: jtrial{at}bcm.tmc.edu
Proteolytic enzymes, released early in the course of an inflammatory response, hydrolyze fibronectin, producing fragments of the parent molecule that alter monocyte phenotype and migratory behavior. Here we test the hypothesis that macrophages, stimulated by the dominant 110120 kd fibronectin fragments (FNf), as are found in lymphatic fluid draining sites of cardiac ischemia-reperfusion injury, produce factors that promote the survival of injured parenchymal cells. Rat splenic macrophages stimulated in vitro with purified FNf produced soluble factors that protected hypoxic rat cardiac myocytes from death by apoptosis. Addition of blocking antibodies specific for tumor necrosis factor-
(TNF-
), fibroblast growth factor-1 (FGF-1), insulin-like growth factor I (IGF-I), and leukemia inhibitory factor (LIF) partly reduced the protection against apoptosis provided to hypoxic cardiac myocytes by cell-free culture supernatants from FNf-stimulated macrophages. Complete blockade of this protection was achieved by a combination of antibodies specific for FGF-1, IGF-I, and LIF. Stimulation of human monocytederived macrophages in vitro with FNf significantly increased their output of TNF-
, FGF-1, IGF-I, and LIF. These results suggest that tissue degradation products, released in the early hours of an inflammatory response, stimulate tissue-infiltrating macrophages to protect injured but still viable parenchymal cells from death by apoptosis.
Key Words: apoptosis cytokines monocytes/macrophages fibronectin ischemia
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