Capacity of monocytic EPCs to promote tubular formations in co-culture with HUVECs in Matrigel®. (a) Representative images of Matrigel® cultures of HUVECs (104) alone, monocytic EPCs (104) from an SSc patient alone, and HUVECs (104) plus monocytic EPCs (104) from an SSc patient and a healthy control. Scale bars = 1 mm. (b) Capacity of monocytic EPCs to enhance the tubular formation was expressed as the ratio of total tube length in the culture of HUVECs plus monocytic EPCs to the length in the culture of HUVECs alone, and compared between SSc patients and healthy controls. Horizontal bars indicate the mean values.