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Paul G. McMenamin, Emily Polla; Mast Cells Are Ubiquitously Distributed In The Choroid Of Fish, Reptiles, Birds, Monotremes, Marsupials And Placental Mammals. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4916.
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Mast cells are bone marrow-derived tissue homing leukocytes, which have been identified in all vertebrate classes. They have traditionally been regarded as effector cells in allergic disorders and certain immune responses to parasites but a broader perspective of their functional heterogeneity, such as immunomodulation, angiogenesis, tissue repair and remodelling after injury is now emerging. The persistence of mast cells throughout the evolution of vertebrates is evidence of strong selective pressure thus suggesting that these cells must have beneficial and important roles. In the context of the mammalian eye mast cells are invariably absent from the neural retina in all species studied to date however they are present within the uveal tract where their role has been more difficult to elucidate. They were once suspected of being critical to susceptibility of experimental autoimmune uveoretinitis in rats and mice. Since then little attention has been given to mast cells although recently their responsiveness to TLR3 ligands and a potential role in age-related macular degeneration has reignited interest in these cells in the healthy and diseased eye. The aim of this study was to determine whether mast cells were present in the choroid of a range of vertebrate classes.
Eye tissues from a range of species (fish, reptiles, birds, marsupials, monotreme, and eutherian mammals) were investigated. Tissues were fixed in gluteraldehyde/paraformaldehyde for resin embedding. Semithin sections of the retina and choroid were cut and stained with toluidine blue.
Mast cells were ubiquitously distributed in the choroid of all species investigated. Their morphology and staining characteristics were remarkably similar from fish through to primates. They were distributed at various depths in the choroid and many were perivascular.
The similar morphology and distribution in mast cells in the choroid of all vertebrate classes studied suggests a basic physiological function that has been retained since early in the evolution of the vertebrate eye.
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