KCs suppress CD8+ T cell activity by several mechanisms, including overexpression of Fas-Ligand, which induces CD8+ T cell destruction (47); overexpression of PD-L1, which leads to cell exhaustion through PD-1 receptor on T cells (48); or secretion of IL-10, an immunosuppressive cytokine (49, 50). This evidence concerns the gene CD8A and dry eye syndrome.