Microchimerism has been defined by the presence of a low number of circulating cells transferred from one individual to another. This transfer takes place naturally during pregnancy, between mother and fetus, or between fetuses in multigestational pregnancies. Furthermore, the establishment of microchimerism can also occur during blood transfusion, as well as during bone marrow and solid-organ transplants. Recently, microchimeric cells have been implicated in the pathogenesis of autoimmune diseases, particularly systemic sclerosis. Studies have demonstrated an increased presence of microchimeric cells in peripheral blood and tissues from patients with systemic sclerosis, and, more recently, microchimeric cells were demonstrated to be specifically activated and capable of recognizing patient human leukocyte antigens.