TNF and renal fibrosis: In sum, this study elucidates the roles of CD74 as key regulators of cyst formation through, (1) activation of PKD associated pathways to regulate cystic renal epithelial cell proliferation, (2) activation of NF-κB to upregulate the expression of TNF-α and MCP-1, resulting in the accumulation of macrophages, (3) transcriptional regulation of the expression of fibrotic markers to regulate renal fibrosis, and (4) transcriptional regulation of the expression of MIF to form a positive feedback loop to regulate cyst growth and renal fibrosis (Figure 9).