Children with Juvenile Dermatomyositis (JDM) have systemic vasculopathy [
1] and manifest the characteristic skin involvement, with or without symmetrical proximal muscle weakness [
2]. Disease activity can be reliably evaluated by disease activity scores (DAS) [
3], and is accompanied by destruction of nailfold capillary end row loops (ERL) [
4]. Autoimmune vascular damage in the inflammatory myopathies is attributed, in part, to endothelial cell damage implemented by proinflammatory cytokines and chemokines, such as Type 1 interferons –IFN-β > IFN-α [
5]. However, the elements of the vasculopathy in JDM remains poorly understood and the role of endothelial progenitor cells (EPCs) has not been defined in these children. EPCs were first isolated two decades ago from human peripheral blood [
6]. These cells can differentiate into mature endothelial cells, which may be incorporated into sites of active angiogenesis and may participate in repair of damaged vascular endothelial cells [
6]. The majority of EPCs are derived from bone marrow and may be mobilized to enter the blood stream by chemokines or angiogenic growth factors [
7]. There are two major methods to identify EPC by fluorescence activated cell sorting (FACS). The first uses both CD34
+ and VEGFR2
+ biomarkers because: a) VEGFR2 is only present on endothelial linage cells such as endothelial progenitor cells and mature endothelial cells; b) CD34 is a marker of stem cells, and c) these double positive cells have the capacity for tube formation [
6]. The second method uses CD34
+/CD133
+ biomarkers that are less specific for EPCs; CD133 is a stem cell marker that is not only present on immature endothelial progenitor cells, but is also found on other cell types such as epithelial cells and cancer stem cells. Of note, EPCs identified by CD34
+ and CD133
+ double positive have not been proven to undergo tube formation, either in vitro or in vivo [
8]. With respect to other related rheumatic diseases, EPC number and functionality is damaged in adults with Polymyositis (PM), but not in adults with Dermatomyositis (DM) [
9]; EPCs are impaired in adults with Systemic Lupus Erythematosus (SLE) [
10] as well as adult Rheumatoid Arthritis (RA) [
11]. It is not known if the EPC number and functionality is impaired in JDM. One factor that potentially might contribute to a decreased EPC number in JDM is that IFN-α, which is increased in JDM sera, has been shown to be biologically active [
12]. The availability of an adequate number of the EPCs may be of importance; it is speculated that EPCs might participate in repairing the characteristic microvasculopathy of JDM [
1,
4]. The purpose of this cross-sectional pilot study was to evaluate EPCs number in fasting children with definite/probable JDM at various stages of disease activity.