Table 1.

Cell types with mesenchymal phenotypes detected in the kidney^a

Cell Type	Markers	Specific Characteristics	References
Resident Fibroblasts	FSP1, HSP47, 5′ectonucleotidase, CD44, ICAM, DDR2	Phenotypic variability between cortical and medullary fibroblasts	41, 44, 63
Myofibroblasts	α-SMA		13
Pericytes	α-SMA, NG2, PDGFR-2, Desmin	Associated capillaries and venoles	64, 65
Vascular smooth muscle cells	α-SMA, caldesmon, calponin	Associated arteries, arterioles, veins	64
EMT-derived fibroblasts	FSP1 (residual epithelial markers?)	Exclusively found in fibrotic kidneys	41, 44
Mesenchymal stem cells	FSP1?		44

↵^a At least 6 distinct cell types with mesenchymal phenotypes can be detected in the kidney. Due to the lack of specific markers, identification of the different lineages can be challenging. In the normal kidney, myofibroblasts can be distinguished from vascular smooth muscle cells and pericytes based on topographical criteria. Without genetic markers, indisputable identification of EMT-derived cells and mesenchymal stem cells is not feasible as of yet. HSP47, heat shock protein 47; ICAM, intracellular adhesion molecule; DDR2, discoidin domain receptor; α-SMA, α-smooth muscle actin; NG2, neuron glial antigen 2; PDGFR, PDGF receptor; EMT, epithelial–mesenchymal transition.