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Heping Xu, Chang Luo, Mei Chen; Retinal pigment epithelial (RPE) cells convert bone marrow derived macrophages into myeloid-derived suppressor cells with a novel phenotype. Invest. Ophthalmol. Vis. Sci. 2013;54(15):144.
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We have shown previously that macrophages/microglia accumulate in the subretinal space in the aging eye. The phenotype and function of subretinal macrophages /microglia remain elusive. Subretinal macrophages are in close contact with retinal pigment epithelial (RPE) cells, which may affect / regulate macrophage functions. The aim of this study was to investigate the effect of RPE cells on the phenotype and function of bone marrow-derived macrophages (BM-DMs).
Bone marrow cells from C57BL/6 mice were cultured in DMEM supplemented with GM-CSF for 5 day to generate BM-DMs. The phenotype of BM-DMs was confirmed by flow cytometry as CD11b+F4/80+MHC-II+Gr1-. Primary RPE cells were cultured from C57BL/6 mice and confirmed by RPE65 and cytokeratin staining. BM-DMs were co-cultured with sub-confluent RPE cells for different times. Macrophages were then collected for phenotypic and functional assays.
Co-culture of BM-DMs with RPE cells results in a time-dependent down-regulation of MHC-II expression and the generation of CD11b+F4/80+Gr1+ myeloid-derived suppressor cells (MDSC). Real-time RT-PCR analysis showed that RPE-induced MDSCs expressed high levels of IL-6, IL-1β, and Arginase-1, but lower levels of IL-12p40 and TNF-α compared to naïve BM-DMs. The expression levels of iNOS, TGF-β and Ym1 did not differ between native BM-DMs and RPE-induced MDSCs. Furthermore, a functional study showed that these MDSCs could suppress anti-CD3 antibody mediated T cell activation and proliferation.
Our results suggest that RPE cells can convert bone-marrow derived macrophages into myeloid-derived suppressor cells under in vitro culture conditions. RPE-induced myeloid-derived suppressor cells are CD11b+F4/80+GR-1+MHC-IIlowIL-6+IL-1β+Arg-1+ and can suppress T cell activation.
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