Maternal microchimerism—Allogenic target of autoimmune disease or Normal Biology?

Chimerism is the state of cells from two distinct individuals living within one body. Fetal cells pass into a mother during pregnancy, where they may persist at low levels for years, creating a state of fetal microchimerism. At the same time, maternal cells pass into the fetus, leading to maternal microchimerism that can persist into adulthood. Hematopoietic stem cell transplantation also creates a state of chimerism, and can lead to a complication of chronic multi-organ inflammation called graft-versus-host disease, (GVHD). The similarities between GVHD and some autoimmune diseases like scleroderma, lupus and myositis suggest that chimerism may be involved in the pathogenesis of both. Maternal and fetal microchimerism in the blood and in tissues have been associated with autoimmune diseases. However, many healthy individuals harbor maternal and fetal cells. Human and animal studies have begun to elucidate the mechanisms for normal tolerance to maternal and fetal microchimeric cells, and how this tolerance may be broken in states of chronic inflammatory disease.