Pregnancy is the major source of natural microchimerism. Pregnancy related microchimerism results from deficiencies in the natural placental physical barrier tissue that divide the maternal circulation from the fetal circulation. As a consequence, there is mutual and bidirectional maternal and fetal cell traffic during pregnancy. Microchimeric cells enter the circulation and persist for many years in the host tissues. These cells are tolerated while acquire specific and diverse biological actions. (Copy of Figure 5 in [1]).
