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Anil Kumar, Lian Zhao, Minhua Wang, Robert Fariss, Wai Wong; Distribution, morphology, and dynamic behavior of macrophages in the adult mouse choroid. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3050.
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Choroidal macrophages are resident ocular immune cells capable of influencing the inflammatory environment of the outer retina and play a role in AMD pathogenesis. However, choroidal macrophages have not been characterized in detail in terms of their anatomy, distribution, behavior, and possible endogenous functions.
Albino, transgenic CX3CR1GFP/+ mice in which choroidal macrophages are labelled with green fluorescent protein (GFP) were used to study macrophage morphology, distribution, and vascular relationships. Live-imaging of GFP+ cells in sclerochoroidal explants was performed to examine the dynamic behavior of choroidal macrophages. The structure of the choroidal vasculature was simultanously visualized by the intravascular perfusion of DiI.
GFP+ macrophages are present throughout the choroid but vary in their morphology, distribution, and vascular associations at each level of the choroidal vascular tree. Perivascular macrophages associated with large choroidal arteries and primary arterioles have elongated, spindle-shaped morphologies aligned with the long axes of vessels, with secondary dendritic processes projecting into the perivascular space. Macrophages associated with smaller terminal arterioles demonstrate a more symmetric, ramified morphology and are mainly positioned within interstitial spaces between vessels and at vessel branch points. Macrophages associated with the choriocapillaris are located only on the scleral, but not the vitreal, choriocapillaris surface and show a flattened morphology with symmetrically ramified processes. Live imaging experiments reveal that choroidal macrophages demonstrate dynamic surveying in their processes but exhibit limited cellular migration. In addition to this predominant population of ramified macrophages which are CD11b+, Iba1+, CD68+, a smaller subpopulation of GFP+ cells with rounded morphologies and a CD11blow/-, Iba1 low/-, CD68 low/- immunophenotype was also observed.
Choroidal macrophages demonstrate morphological diversity and varied associations with the choroidal vasculature at each level. Their dynamic process behavior and close vascular associations suggest that they may play functional roles in vasoregulation and vascular surveillance in the choroid.
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