Under normal conditions, KCs secrete prostaglandin E2 (PGE2), transforming growth factor beta (TGF-β), and IL-10 [46], and express Fas-L and PD-L1 on the cell membrane [72,73] (Figure 2), playing a role in maintaining immune hyporesponsiveness/immunotolerance and leading to the differentiation of more hepatic Treg cells. This evidence concerns the gene FASLG and dry eye syndrome.