Decreased circulating lymphatic endothelial progenitor cells in digital ulcer-complicated systemic sclerosis

In systemic sclerosis (SSc), the main pathogenic scenario is represented by early endothelial cell injury and microvascular desertification culminating into skin and internal organ fibrosis.1 Growing evidence suggests that impaired vascular repair and neovascularisation could be related to failure of both angiogenesis and endothelial progenitor cell (EPC)-driven vasculogenesis.2 In SSc, the majority of studies are focused on the role of blood vessel dysfunction,1 2 while the involvement of the lymphatic microcirculation has attracted much less attention. Nevertheless, clinical and histological findings have shown that lesional SSc skin displays lymphatic circulatory abnormalities.3–5 These may be present since the earliest disease phases, when digital painless swelling (puffy fingers), due to the accumulation of protein-rich interstitial fluid (ie, oedema), is a clinical hallmark.3–5 Furthermore, in SSc reduced numbers of dermal microlymphatics have been correlated with development of digital ulcers (DU) and progression of cutaneous fibrosis.4 5 Postnatal lymphatic neovascularisation takes place through lymphangiogenesis (ie, the formation of novel lymphatic vessels from pre-existing ones) and lymphvasculogenesis. This last event stems from circulating bone marrow-derived lymphatic EPC (LEPC) that differentiate into mature endothelial cells expressing lymphatic-specific markers.6 On their surface, LEPC display CD34 and CD133, likewise their blood vascular counterpart (ie, EPC), but they …