C3 and cyst: Alternatively activated “M2-like” anti-inflammatory kidney macrophages, which are uniquely situated in close apposition to endothelial cells and basement membrane, have been shown to promote cyst growth in ADPKD by driving proliferation and fibrosis in the cystic epithelium, in part by induction of complement components including C3, TGF-ß, and connective tissue growth factor (CTGF)[54, 89, 90].