LYVE-1-positive macrophages are present in normal murine eyes.
OBJECTIVE
A functioning lymphatic system is necessary not only to permit the organism to mount a rapid and effective immune response but, even more so, to maintain tissue fluid homeostasis. However, no clear evidence of lymphatic vessels draining intraocular and orbital tissues--retina, choroid, sclera, and extraocular muscles--exists.


METHODS
Ocular tissue flatmounts from normal or enhanced green fluorescence protein (EGFP) chimeric mice were immunostained for lymphatic endothelium hyaluronan receptor (LYVE-1, a routinely used lymphatic endothelial marker), podoplanin, Flt4/VEGFR3, Sca-1, CD11b, or F4/80 and were observed by confocal microscopy. Single-cell suspensions from ocular tissues were also prepared and were analyzed by flow cytometry.


RESULTS
Lymphatic vessels were detected in the posterior regions of the extraocular muscles and the connective tissues of the extraocular muscle cones in the normal mouse. No typical lymphatic vessels were found within the eye. A large population of LYVE-1(+) nonendothelial cells, distributed as single cells, was detected in all ocular tissues except the central cornea. These cells also express another lymphatic endothelial cell marker, Flt4/VEGFR3, but not podoplanin, and they have hyaluronan-binding ability. Bone marrow chimerism studies indicated that the LYVE-1(+) cell populations are bone marrow derived and have a slow turnover in ocular tissues (3-6 months). Phenotype analysis revealed that nonendothelial LYVE-1(+)cells in the sclera, choroid, and iris included CD11b(+)F4/80(+) macrophages, CD11b(+)F4/80(-) macrophages, and CD11b(-)F4/80(-) bone marrow-derived cells. All LYVE-1(+) cells in the retina were CD11b(+)F4/80(+) macrophages. Cells in the limbus and the iris root also express Sca-1, suggesting that they are hematopoietic lymphatic vessel progenitor cells.


CONCLUSIONS
These observations suggest that a lymphatic system exists for the transport of immune cells and fluids from the posterior segment of the eye, that ocular tissues are rich in bone marrow-derived LYVE-1(+) macrophages under normal physiological conditions, and that a subpopulation of these cells may represent resident precursor cells necessary for the de novo formation of ocular/orbital lymphatic vessels in pathologic conditions.
Xu
Heping
H
Department of Ophthalmology, School of Medicine, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom. h.xu@abdn.ac.uk
Chen
Mei
M
Reid
Delyth M
DM
Forrester
John V
JV
D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D000067696:Ataxin-1; D000067528:Ataxins; D015415:Biomarkers / Q000378:metabolism; D039481:CD11b Antigen / Q000378:metabolism; D002678:Chimera; D003228:Conjunctiva / Q000378:metabolism; D003238:Connective Tissue / Q000378:metabolism; D005123:Eye / Q000378:metabolism*; D005434:Flow Cytometry; D006023:Glycoproteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D016850:Limbus Corneae / Q000378:metabolism; D042601:Lymphatic Vessels / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D009801:Oculomotor Muscles / Q000378:metabolism; D014602:Uvea / Q000378:metabolism; D040321:Vascular Endothelial Growth Factor Receptor-3 / Q000378:metabolism; D000098853:Podoplanin
D000943:Antigens, Differentiation; D000067696:Ataxin-1; D000067528:Ataxins; D015415:Biomarkers; D039481:CD11b Antigen; D006023:Glycoproteins; D049452:Green Fluorescent Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D040321:Vascular Endothelial Growth Factor Receptor-3; C000593750:Atxn1 protein, mouse; C490441:Pdpn protein, mouse; D000098853:Podoplanin; C492273:LYVE1 protein, mouse; C485184:enhanced green fluorescent protein; C036763:monocyte-macrophage differentiation antigen