Fibrocytes in Scleroderma Lung Fibrosis

Systemic sclerosis (SSc) or “Scleroderma” is a disease characterized by cutaneous and visceral fibrosis that affects both the skin and internal organs. The worldwide prevalence ranges from 50-300 cases per million (Chifflot et al., 2008) and much of the morbidity in this population results from pulmonary complications. In fact, nearly 70% of scleroderma patients show some form of lung disease. Of the two forms of lung involvement, pulmonary arterial hypertension and interstitial lung disease, the latter has emerged as the greatest cause of death in these patients. The lungs of patients with scleroderma associated interstitial lung disease (SSc-ILD) exhibit replacement of the normal lung architecture with inflamed and fibrotic tissue that cannot participate in gas exchange. While approximately 42% of patients with SSc-ILD die of disease progression within ten years of diagnosis (Steen & Medsger, 2007) evidence is emerging that some patients progress slowly and in some cases spontaneously improve while others follow an accelerated clinical course (Goh et al., 2008). There is currently no way to predict which patients will progress rapidly and require more intensive therapy (Daoussis et al., 2010 ; Swigris et al., 2006; Tashkin et al., 2006) and/or referral for lung transplantation (D'Ovidio et al., 2005a; D'Ovidio et al., 2005b); and which patients will follow a more indolent course requiring less intense follow up. Therefore the development of a clinically predictive measure of pathologic progression would benefit physicians caring for patients with this disease. The ideal biomarker would be present in easily accessible clinical specimens, would be a potential contributor to disease development, and would be easily studied in murine models of disease. For this reason, peripheral blood fibrocytes have emerged as an exciting new area of study in the field of Scleroderma (Gan et al., 2011; Mathai et al., 2010; Peng et al., 2011 ; Tourkina et al.,2011; Reilkoff et al., 2011).