title: Macrophages in the external muscle layers of mammalian intestines.
abstract: The literature on macrophages in the muscularis externa of mouse, rat, guinea pig, cat, dog and human gut is reviewed. In smaller mammals macrophages are regularly situated in two locations: in the serosa and at the level of Auerbach's plexus between the longitudinal and circular muscle layers. In addition a few solitary cells are present at the level of the deep muscular plexus. At the level of Auerbach's plexus the macrophages occur as a constant and regularly distributed cell population with intimate associations between macrophages and interstitial cells of Cajal. Morphologically they differ from most resident macrophages in being irregular in shape with 4-6 primary cytoplasmic processes, which branch and give a stellate appearance. They have been demonstrated with endocytotic markers (trypan red, FITC-dextran, cholera toxin), immunocytochemically with macrophage antibodies (F4/80, M1/70) and antibodies against MHC class-II antigen, GABA and cGMP. In muscularis externa of the human gut a regularly distributed cell population of macrophages is not obvious. However, a phenotypically distinct subgroup is identified by light microscopy with the pan macrophage antibodies (EBM11, C3b1 and partly by p150.95), and shows MHC class-II antigen. By electron microscopy muscularis externa macrophages, in all species investigated, appear to be endocytically downregulated, and since they are lysozyme, prostaglandine H synthase (both constitutive and activated) and acid phosphatase negative, they appear to be inactivated cells. Both origin and function of these cells are unknown. They may be immuno-competent, participate in a neuroimmune axis, tissue growth and modulation or other regulations of specific cell functions.
authors.affiliation: Department of Anatomy, Panum Institute, University of Copenhagen, Denmark.
authors.forename: H B
authors.initials: HB
authors.lastname: Mikkelsen
mesh_terms: D000818:Animals; D002415:Cats; D004285:Dogs; D006168:Guinea Pigs; D006801:Humans; D007422:Intestines / Q000166:cytology* / Q000648:ultrastructure; D008264:Macrophages / Q000502:physiology* / Q000648:ultrastructure; D008322:Mammals / Q000502:physiology*; D051379:Mice; D009130:Muscle, Smooth / Q000166:cytology* / Q000648:ultrastructure; D051381:Rats