title: Macrophage response to peripheral nerve injury: the quantitative contribution of resident and hematogenous macrophages.
abstract: Whereas local microglial cells of the CNS rapidly respond to injury, little is known about the functional role of resident macrophages of the peripheral nervous system in nerve pathology. Using bone marrow chimeric rats, we recently identified individual resident endoneurial macrophages that rapidly became activated after nerve injury. However, the extent of local macrophage activation and its quantitative contribution to the total macrophage response is unknown. We now have created chimeric mice by transplanting bone marrow from green fluorescent protein (GFP)-transgenic mice into irradiated wild-type mice, allowing easy differentiation and quantification of hematogenous and resident endoneurial macrophages. After sciatic nerve crush injury, both GFP(-) and GFP(+) resident macrophages, the latter having undergone physiological turnover from the blood before injury, rapidly underwent morphological alterations and increased in number. Proliferating GFP(-) and GFP(+) resident macrophages were abundant and peaked 3 days after injury. A major lesion-induced influx of hematogenous macrophages with a disproportionate increase of GFP(+) macrophages was not observed until Day 4. Throughout all time points examined, GFP(-) resident macrophages were strikingly frequent, reaching maximum numbers 9.5-fold above baseline. There was also a notable proportion of GFP(-) resident endoneurial macrophages phagocytosing myelin and expressing major histocompatibility complex class II. Our results demonstrate for the first time that the rapid response of resident endoneurial macrophages to nerve injury is quantitatively important and that local macrophages contribute significantly to the total endoneurial macrophage pool during Wallerian degeneration.
authors.affiliation: Department of Neurology, Universitätsklinikum Münster, Münster, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Mueller
authors.forename: Christine
authors.initials: C
authors.lastname: Leonhard
authors.forename: Karin
authors.initials: K
authors.lastname: Wacker
authors.forename: E Bernd
authors.initials: EB
authors.lastname: Ringelstein
authors.forename: Masaru
authors.initials: M
authors.lastname: Okabe
authors.forename: William F
authors.initials: WF
authors.lastname: Hickey
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kiefer
mesh_terms: D000818:Animals; D017209:Apoptosis; D016026:Bone Marrow Transplantation; D002452:Cell Count; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000145:classification / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009409:Nerve Crush; D010525:Peripheral Nerves / Q000378:metabolism / Q000473:pathology; D011828:Radiation Chimera; D012584:Sciatic Nerve / Q000293:injuries / Q000378:metabolism / Q000473:pathology*; D014855:Wallerian Degeneration / Q000209:etiology / Q000473:pathology
chemical_list: D007202:Indicators and Reagents; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins