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S. W. McPherson, N. D. Heuss, K. L. Lew, D. A. Ferrington, D. S. Gregerson; RPE Cells Induce Unresponsiveness and Treg Activity in Naive T Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5200.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal pigmented epithelial (RPE) cells are thought to contribute to retinal immune privilege. We previously reported that antigen activation of naïve CD4 T cells in the presence of RPE upregulated the expression of CD69 and CD44, indicating T cell receptor (TCR) occupancy, but production of cytokines was repressed. Although CD25 was upregulated on RPE-activated T cells, they were unresponsive to exogenous IL-2. Here we further examined the immunoregulatory properties of RPE in vitro, focusing on activities that inhibit activation of NFAT-dependent cytokine production, since this would contribute to the loss of lymphocyte activities.
A Jurkat cell line was transfected with a secreted form of placental alkaline phosphatase (SEAP) regulated by the NFAT promoter, leading to high levels of SEAP production when Jurkat cells were stimulated through their TCR using mAb C305. RPE cells and supernatants were tested for effects on Jurkat cell activation using this reporter system. Naïve CD4 T cells from TCR Tg mice were also used to assay the immunoregulatory effects of RPE cells.
TCR Tg T cells recovered from RPE co-cultures did not express foxP3 above control levels, but did exhibit regulatory activity. RPE co-cultured TCR Tg T cells were unable to produce full cytokine responses upon challenge with Ag and splenic APC. T cell viability in the presence of RPE was elevated. RPE supernatant, with or without TGF-b, did not inhibit NFAT regulated SEAP levels in Jurkat cells. Instead there were increased SEAP levels independent from the stimulation provided by C305 TCR ligation. Jurkat cells also increased baseline levels of SEAP when cultured in direct contact with RPE cells. However, Jurkat cells in direct contact with RPE exhibited reduced SEAP levels following C305 stimulation.
RPE produces a cell-free activity that stimulates the NFAT promoter. Since NFAT activation results from an increase in intracellular calcium, the results suggest that RPE cells produce a calcium response in Jurkat cells. This mechanism suggests a pathway by which RPE cells can regulate immune responses since increased levels of cytoplasmic calcium in T cells in the absence of co-stimulatory signals can lead to anergy.
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