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Sunao Sugita, Yoshihiko Usui, Shintaro Horie, Yuri Futagami, Hiroyuki Aburatani, Taku Okazaki, Tasuku Honjo, Masaru Takeuchi, Manabu Mochizuki; T-Cell Suppression by Programmed Cell Death 1 Ligand 1 on Retinal Pigment Epithelium during Inflammatory Conditions. Invest. Ophthalmol. Vis. Sci. 2009;50(6):2862-2870. doi: 10.1167/iovs.08-2846.
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purpose. To determine whether retinal pigment epithelial (RPE) cells can inhibit in vitro T-cell activation during inflammatory conditions.
methods. Primary cultured RPE cells were established from normal C57BL/6 mice. Target bystander T cells were established from normal splenic T cells with anti-CD3 antibodies. T-cell activation was assessed for proliferation by both examining [3H]-thymidine incorporation and the production of interferon (IFN)γ or IL-17, as determined by ELISA. Expression of programed cell death 1 ligand 1 (PD-L1) on RPE or recombinant mouse IFNγ-pretreated RPE cells was evaluated using oligonucleotide microarray, RT-PCR, immune staining, and flow cytometry. Expression of programed cell death 1 (PD-1)+ on target T cells was evaluated by flow cytometry. Anti-mouse PD-L1 or PD-L2 neutralizing antibodies or target T cells from PD-1 knockout donors were used for the assay.
results. IFNγ-pretreated RPE greatly suppressed activation of bystander T cells, especially the IFNγ production by the target T cells (Th1 cells, but not Th17 cells) via direct cell contact. By examining cell surface candidate molecules, IFNγ-pretreated RPE expressed much higher levels of PD-L1 compared with the control nontreated RPE. Although primary RPE did not express the costimulatory molecule, expression of the molecule was induced on the surface of IFNγ-pretreated RPE. PD-L1+ RPE in the presence of IFNγ selectively suppressed PD-1+ T-cell activation. IFNγ-pretreated RPE in the presence of anti-PD-L1 neutralizing antibodies, but not anti-PD-L2, failed to suppress T-cell production of IFNγ. In addition, these RPE cells failed to suppress the production of IFNγ by CD4+ T cells from PD-1 null donors.
conclusions. Suppression of T-cell activation was obtained in cultures only when RPE expressed negative costimulators. Therefore, the authors propose that in vitro, Th1 cytokine-exposed ocular resident cells can express this molecule and it is this expression that causes the suppression of the bystander Th1-type cells.
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