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Christopher M Reilly, Shin Ae Park, Carl F Marfurt, Brian C Leonard, Christopher J Murphy; Leukocyte phenotype and lymphatic vessel distribution in canine lacrimal and nictitating glands. Invest. Ophthalmol. Vis. Sci. 2014;55(13):53.
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© ARVO (1962-2015); The Authors (2016-present)
To better understand immune cells and lymphatics in normal canine tear glands, which have not been previously described to our knowledge. Dogs are a valuable, spontaneous animal model of dry eye diseases.
Lacrimal and third eyelid glands were collected from normal young adult dogs < 2 hours post euthanasia. Glands were formalin fixed, processed, paraffin-embedded, and sectioned. Immunohistochemistry was performed with antibodies against: CD3 (T-cells); CD20 (B-cells); CD18 (leukocytes, especially macrophages); and LYVE-1 (lymphatic endothelial cells, some leukocytes), using protocols validated for use in dogs. PBS was negative control. Leukocytes expressing CD3, CD20, and LYVE-1 were enumerated in acinar tissue (cells/10 400x fields). Antigen expression in periductal, interstitial, and peripheral regions was assessed on a 0 to 3 scale (0=absent; 3=heavy infiltrates), due to lack of uniform consecutive fields. CD18 expression was assessed descriptively, to identify leukocytes not labeled by other antibodies (e.g. macrophages, dendritic cells). The density of lymphatic vessels was also assessed on a 0-3 scale in acinar, interlobular, and peripheral regions.
CD20+ B cells were over 4 times more prominent than CD3+ T cells in all glands. B cells were distributed in interacinar clusters, with T-cells more individually scattered. All lymphocytes were rare in connective tissue septa, and surrounded ducts in low numbers. LYVE-1+ leukocytes and channels were present in low density in all connective tissue, and absent in acinar lobules. CD18 expression in connective tissue largely mirrored LYVE-1 expression, supporting leukocyte origin of LYVE-1+ cells. Cells that were exclusively CD18+, suggesting macrophage/dendritic cell identity, were uniquely distributed tightly surrounding and investing acinar epithelium.
T cells, B cells, macrophages, and dendritic cells are all present, with unique distributions, in the canine lacrimal glands. To our knowledge, this is the first report of non-endothelial LYVE-1+ cells in the dog, or in the lacrimal tissues of any species. The role of LYVE-1+ leukocytes and dendritic cells in canine lacrimal immunity warrants further investigation. Lymphatic presence in canine lacrimal tissue is confirmed, and is relatively minor, which may be important in lacrimal immune regulation and possibly lacrimal tumor metastasis.
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