CD74 and cyst: Consistent with the findings in Pkd1flox/flox:Ksp-Cre mice, we found that knockout of CD74 also delayed cyst growth in postnatal day 21 (PN21) Pkd1flox/flox:Pkhd1-Cre:CD74−/− kidneys (n = 8) compared to that in age matched Pkd1flox/flox:Pkhd1-Cre:CD74+/+ kidneys (n = 10) (Figure 2A) characterized by the decrease of cystic index, KW/BW ratios and BUN levels (Figure 2B–D) as well as cyst lining epithelial cell proliferation as examined by Ki67 staining (Figure 2E), but induced cyst lining epithelial cell apoptosis as examined by TUNEL assay (Figure 2F).