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Wanhua Yang, Haochuan Li, Peter W. Chen, Hassan Alizadeh, Yuguang He, R. Nick Hogan, Jerry Y. Niederkorn; PD-L1 Expression on Human Ocular Cells and Its Possible Role in Regulating Immune-Mediated Ocular Inflammation. Invest. Ophthalmol. Vis. Sci. 2009;50(1):273-280. doi: 10.1167/iovs.08-2397.
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purpose. To assess the expression of PD-L1 and PD-L2 on human ocular cells and their potential to regulate ocular inflammation.
methods. Five categories of human ocular cells were evaluated for PD-L1 and PD-L2 expression by RT-PCR and flow cytometry. Three normal eyes and an inflamed eye from a patient with sympathetic ophthalmia were examined by immunohistochemistry for in situ PD-L1 expression. The immunomodulatory functions of PD-L1 and PD-L2 were tested by coculturing untreated or IFN-γ–pretreated ocular cells with activated human peripheral blood T cells for 48 hours and assessing T-cell production of IFN-γ, TNF-α, IL-4, and IL-5 by ELISA and T-cell apoptosis by flow cytometry.
results. PD-L1 protein was expressed constitutively in 4 of 5 human ocular cell lines, and its expression was significantly upregulated after stimulation by IFN-γ. Moreover, in situ expression of PD-L1 in inflamed ocular tissues was remarkably upregulated compared with normal eyes. Although PD-L2 expression was detectable by flow cytometry on 3 of 5 ocular cell lines, immunohistochemical staining did not show expression of PD-L2 on either normal or inflamed ocular tissues. IFN-γ, TNF-α, and IL-5 production by activated T cells cocultured with ocular cells was significantly enhanced in the presence of anti–PD-L1 blocking antibody. However, ocular cell–expressed PD-L1 and PD-L2 did not induce T-cell apoptosis.
conclusions. PD-L1 expressed on human ocular cells has a presumptive role in controlling ocular inflammation by inhibiting the production of proinflammatory cytokines and a Th2 cytokine by activated T cells. This may represent an important mechanism for maintaining immune privilege in the eye.
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