For instance, while it is well known that TGF-β1 expression is increased in almost all of the chronic kidney disease models studied, the expression of TGF-β receptors, which determine the specificity of TGF-β action, is often up-regulated predominantly in renal tubular epithelium [97], indicating that tubular epithelial cells are the in vivo natural targets of this pro-fibrotic cytokine. Here, TGFB1 is linked to chronic kidney disease.