Autoantibodies to Estrogen Receptor a in Systemic Sclerosis (SSc) as Pathogenetic Determinants and Markers of Progression

Systemic sclerosis (SSc) is a multisystem autoimmune disease of unknown etiology characterized by inflammation, autoantibody production, and fibrosis. It predominantly affects women, this suggesting that female sex hormones such as estrogens may play a role in disease pathogenesis. However, up to date, the role of estrogens in SSc has been scarcely explored. The activity of estrogens is mediated either by transcription activity of the intracellular estrogen receptors (ER), ER alpha and ER beta, or by membrane-associated ER. Since the presence of autoantibodies to ERa and their role as estrogen agonists interfering with T lymphocyte homeostasis were demonstrated in other autoimmune diseases, we wanted to ascertain whether anti-ERa antibodies were detectable in sera from patients with SSc. We detected anti-ERa antibody serum immunoreactivity in 42% of patients with SSc (30 out of 71 analyzed). Importantly, a significant association was found between anti-ERa antibody values and key clinical parameters of disease activity and severity. Fittingly, anti-ERa antibody levels were also significantly associated with alterations of immunological features of SSc patients, including increased T cell apoptotic susceptibility and changes in T regulatory cells (Treg) homeostasis. In particular, the percentage of activated Treg (CD4(+) CD45RA(-) FoxP3(bright) CD25(bright)) was significantly higher in anti-ERa antibody positive patients than in anti-ERa antibody negative patients. Taken together our data clearly indicate that anti-ERa antibodies, probably via the involvement of membrane-associated ER, can represent: i) promising markers for SSc progression but, also, ii) functional modulators of the SSc patients' immune system.