Macrophage arginine metabolism to ornithine/urea or nitric oxide/citrulline: a life or death issue.
Macrophages can metabolize arginine to nitric oxide in quantities that inhibit pathogens or nearby host cells. They can instead metabolize arginine to ornithine (a precursor of polyamines and collagen) in quantities that stimulate pathogens or nearby host cells. Macrophages are essentially the only circulating cells that can make these life or death decisions with arginine. Macrophages expressing these destructive or constructive phenotypes have been termed M-1 or M-2 because they also stimulate TH1 or TH2 responses, respectively. Factors that influence whether a macrophage expresses the M-1 or M-2 phenotype and the real or potential impact on immune responses and other host processes are discussed.
Mills
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Department of Surgery and Diabetes Institute for Immunology and Transplantation, University of Minnesota Hospitals and Clinics, Minneapolis 55455, USA. mills002@tc.umn.edu
D000818:Animals; D001119:Arginase / Q000096:biosynthesis; D001120:Arginine / Q000378:metabolism*; D016923:Cell Death; D002470:Cell Survival; D002956:Citrulline / Q000378:metabolism*; D006801:Humans; D008214:Lymphocytes / Q000276:immunology; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II; D009952:Ornithine / Q000378:metabolism*; D014508:Urea / Q000378:metabolism*
D002956:Citrulline; D009569:Nitric Oxide; D014508:Urea; D001120:Arginine; D009952:Ornithine; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D001119:Arginase