In addition, the cyst lining epithelial cell proliferation as examined with Ki67 staining was decreased (Figure 1E) and the cystic lining epithelial cell apoptosis as examined with TUNEL assay was increased (Figure 1F) in Pkd1 and CD74 double knockout kidneys compared to that in Pkd1 conditional knockout but CD74 wild type kidneys. Here, CD74 is linked to cyst.