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V. Montalvo, M. M. Campos, J.-Y. Tsai, R. N. Fariss, D. McVicar, I. Gery; DAP12 Expressed at High Levels in Retinal Capillaries. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5216.
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DAP12 is an ITAM-containing signaling adaptor molecule conveying activating properties to surface receptors on many lymphoid cell types, including peripheral blood monocytes, macrophages, dendritic cells, glia, osteoclasts, and NK cells. Among their other activities, DAP12 and its ligand, TREM2, inhibit development of inflammation (Hamerman, J Immunol 2006). A deficiency of functional DAP12 in humans results in Nasu-Hakola Disease, a syndrome characterized by bone cysts and presenile dementia. Unexpectedly, we found that DAP12 is also expressed on retinal capillaries and the purpose of this study is to characterize the expression of this molecule in the eye, as well as in other tissues.
Tissues were collected from BALB/c mice and frozen in OCT. Cryosections were fixed briefly and immunolabeled with an antibody to DAP12 and isolectin IB4, an endothelial cell-specific marker. Samples were imaged by confocal microscopy to evaluate the distribution and intensity of DAP12 labeling.
We found that DAP12 is specifically expressed by endothelial cells in retinal capillaries, as confirmed by co-staining with isolectin IB4, a marker for endothelial cells. On the other hand, no staining for DAP12 was found on blood vessels of the limbus or choroid. In addition to the retina, we found that DAP12 is expressed on blood vessels of the brain, heart and liver, and on other cells in the lung and spleen. Surprisingly, however, blood vessels in the mouse kidney were not stained with DAP12. Staining with the DAP12 antibody in the retinal capillaries was more intense than in other tissues.
DAP12, a major signaling molecule of the immune system, is strongly expressed by endothelial cells of the retinal capillaries, as well as blood vessels of certain other organs. Since endothelial cells of the retinal capillaries serve as a barrier to circulating immune cells, the presence of DAP12 in the retinal vasculature may reflect this protein’s contribution to this critical barrier.
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