Tubular-like structure formation in Matrigel after 48 hrs. (a) Expression of endothelial cell markers CD31 (PECAM-1), CD34, CD144 by flow cytometric analysis. The histograms in each graph show the increase in fluorescence for each endothelial cell marker (green line) compared with the expression of an isotype-matched irrelevant monoclonal antibody (mAb) used as control (purple line). (b) Phase contrast pictures: healthy control (HC)-epithelial cells (ECs) cultured alone form well-organized tube-like structures; systemic sclerosis (SSc)-ECs cultured alone failed to form well-organized tube-like structures; HC-ECs/HC-mesenchymal stem cells (MSCs) co-culture: the picture shows an increased ability to form a well-organized tube-like network; SSc-ECs/HC-MSCs co-culture: a decreased capacity of HC-MSCs to improve the tubular formation by SSc-ECs when cultured alone can be observed; HC-ECs/SSc-MSCs co-culture: the presence of SSc-MSCs did not influence the ability of HC-ECs to form normal tubular structures, when cultured alone; SSc-ECs/SSc-MSCs co-culture: the impairment to form tubular structures of SSc-ECs was not improved by SSc-MSCs. The fluorescent images show EC (green) and MSC (red) distribution. Pictures are representative of all experiments. Original magnification 20×. (c) The tube formation was measured as cells/mm and the performance in each experiment was expressed by the ratio: total tube length in each culture condition/length in the culture of HC-ECs alone (**P = 0.0002). Results are expressed as median (range) of triplicate experiments.