When the proportion of blood vessels carrying endothelial cells expressing human CD31 was evaluated, fewer monocytic EPCs from SSc patients were incorporated into the vascular wall than monocytic EPCs from healthy controls; this difference was statistically significant when 104 and 105 monocytic EPCs were used for transplantation (P = 0.03 for both comparisons, Figure 8c). This evidence concerns the gene PECAM1 and systemic sclerosis.