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D.S. Gregerson, T.N. Sam, J. Yang; The Antigen Presenting Activity of Fresh and Cultured CD45+ Cells From the Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1055.
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Purpose: Several lines of investigation indicate that Ag recognition takes place in the retina, or that retina-derived Ag is recognized elsewhere. To explore the possibility that cells from the retina are capable of presenting Ag directly to CD4 T cells, CD45+ cells were isolated from retina and tested in vitro for the ability to present specific Ag to naïve and Ag-experienced CD4 T cells. Methods: Retinas were harvested and enzymatically dissociated. The cell suspension was separated on a density gradient, and the buoyant cells positively selected with anti-CD45 by magnetic cell separation. The resulting population was cultured with naïve and Ag-experienced TCR-Tg CD4 T cells specific for beta-galactosidase. In some cases, the retinal cells were activated with IFN-gamma, anti-CD40 or LPS. Spleen cells, or fractions of spleen cells were used as positive controls for Ag presentation. The T cells were recovered and analyzed by flow cytometry to determine their numbers and activation status. Measures of activation including changes in CD44, CD45RB, CD62L, CD69 and size. In some experiments, T cells were labeled with CFSE prior to culture. Results: Retinal CD45+ cells were poorly able to support an Ag-dependent proliferative response in both naive and antigen-experienced T cells, unlike the spleen cells, which supported a potent response in both populations. Activation of the retinal cells in vitro with IFN-gamma, anti-CD40 or LPS increased their activity as APC to a small degree, but it remained well below the activation observed in parallel cultures with spleen cells or CD11c-enriched splenic APC. Addition of retinal CD45+ cells to co-cultures of T cells and spleen cells reduced the proliferative response of the T cells. Analysis of activation markers on the T cells cultured with Ag and the retinal CD45+ cells revealed small differences, suggesting that some ligation of the TCR had taken place, but that little proliferation resulted from that interaction. Conclusions: Although some CD45+ cells from the retina express class II MHC, and costimulatory molecules (CD80), the ability of these cells to support Ag-dependent proliferative responses in Ag-specific T cells is minimal. Their APC activity is not much enhanced by pre-treatment with activators including IFN-gamma, anti-CD40 and LPS. Since they give some evidence of the ability to ligate the TCR, we speculate that they may be inducing a regulatory response in the T cells.
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