Telocytes express PDGFR-alpha in the human gastrointestinal tract

Telocytes (TC), a cell population located in the connective tissue of many organs of humans and laboratory mammals, are characterized by a small cell body and extremely long and thin processes. Different TC subpopulations share unique ultrastructural features, but express different markers. In the gastrointestinal (GI) tract, cells with features of TC were seen to be CD34-positive/c-kit-negative and several roles have been proposed for them. Other interstitial cell types with regulatory roles described in the gut are the c-kit-positive/CD34-negative/platelet-derived growth factor receptor a (PDGFRa)-negative interstitial cells of Cajal (ICC) and the PDGFRa-positive/c-kit-negative fibroblast-like cells (FLC). As TC display the same features and locations of the PDGFRa-positive cells, we investigated whether TC and PDGFRa-positive cells could be the same cell type. PDGFRa/CD34, PDGFRa/c-kit and CD34/c-kit double immunolabelling was performed in full-thickness specimens from human oesophagus, stomach and small and large intestines. All TC in the mucosa, submucosa and muscle coat were PDGFRa/CD34-positive. TC formed a three-dimensional network in the submucosa and in the interstitium between muscle layers, and an almost continuous layer at the submucosal borders of muscularis mucosae and circular muscle layer. Moreover, TC encircled muscle bundles, nerve structures, blood vessels, funds of gastric glands and intestinal crypts. Some TC were located within the muscle bundles, displaying the same location of ICC and running intermingled with them. ICC were c-kit-positive and CD34/PDGFRa-negative. In conclusion, in the human GI tract the TC are PDGFRa-positive and, therefore, might correspond to the FLC. We also hypothesize that in human gut, there are different TC subpopulations probably playing region-specific roles.