Figure 2. |. Proposed functions of resident macrophages during cyst formation and expansion.

Multiple processes occur during cyst formation and expansion, including increased epithelial proliferation and apoptosis, interstitial inflammation, increased extracellular matrix deposition and renal fibrosis, and vasculature abnormalities. Resident macrophages may be involved in controlling several of these processes directly or indirectly. It has been proposed that resident macrophages can promote cystic epithelial proliferation by secretion of cytokines and phagocytosis of apoptotic epithelial cells. Also, renal-resident macrophages may drive interstitial myofibroblast activation and proliferation, leading to increased extracellular matrix deposition and renal fibrosis. Resident macrophages may serve as “first responders” in the kidney and control the accumulation and effector function of other immune cells, such as neutrophils, infiltrating macrophages, and T cells, to indirectly regulate cyst formation. Finally, renal resident macrophages may also regulate vasculature abnormalities through their proposed proangiogenic functions. The inset indicates the reciprocal communication between resident macrophages and the cilia mutant epithelium via mb-CSF1/CSF-1R. ECM, extracellular matrix; mb-CSF1, membrane-bound colony-stimulating factor-1; RM, resident macrophages; IM, infiltrating macrophages.