Abstract
A great interest has developed over the last several years in research on interstitial Cajal-like cells (ICLCs), later renamed to telocytes (TCs). Such studies are restricted by diverse limitations. We aimed to critically review (sub)epicardial ICLCs/TCs and to bring forward supplemental immunohistochemical evidence on (sub)epicardial stromal niche inhabitants. We tested the epicardial expressions of CD117/c-kit, CD34, Cytokeratin 7 (CK7), Ki67, Platelet-Derived Growth Factor Receptor (PDGFR)-α and D2-40 in adult human cardiac samples. The mesothelial epicardial cells expressed D2-40, CK7, CD117/c-kit and PDGFR-α. Subepicardial D2-40-positive lymphatic vessels and isolated D2-40-positive and CK7-positive subepicardial cells were also found. Immediate submesothelial spindle-shaped cells expressed Ki-67. Submesothelial stromal cells and endothelial tubes were PDGFR-α-positive and CD34-positive. The expression of CD34 was pan-stromal, so a particular stromal cell type could not be distinguished. The stromal expression of CD117/c-kit was also noted. It seems that epicardial TCs could not be regarded as belonging to a unique cell type until (pre)lymphatic endothelial cells are inadequately excluded. Markers such as CD117/c-kit or CD34 seem to be improper for identifying TCs as a distinctive cell type. Care should be taken when using the immunohistochemical method and histological interpretations, as they may not produce accurate results.
Highlights
Telocytes (TCs) were proposed in 2010 as being stromal cells morphologically different from other interstitial resident cells [1]
Beneath the mesothelial layer, lumina-presenting, thin, lymphatic vessels with circumferential dispositions were labelled with the D2-40 marker (Figure 1)
We noted that the endothelial cells of longitudinally cut lymphatic vessels could have a TC-like appearance, but the identification of lumina made the distinction between these cell types (Figure 1)
Summary
Telocytes (TCs) were proposed in 2010 as being stromal cells morphologically different from other interstitial resident cells [1]. They were previously considered interstitial Cajal-like cells (ICLCs) [2,3,4,5,6,7,8,9,10]. The immunophenotype of TCs ‘is similar to that of interstitial, endothelial, smooth muscle, mast and haematopoietic stem cells and neurons’ [18]. TCs, as a group, could be the result of a lack of uniformity and consensus in the terminology relating
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