Microchimerism and Reproduction: Both Self and Not Self.

Maternal-fetal exchange during pregnancy creates a long-term legacy of naturally acquired microchimerism (Mc) for child and mother. Mc is harboring a small amount of cells (or DNA) that originated in a different individual. The durability and pleiotropic nature of Mc is evident; both maternal and fetal origin Mc are found in immune cellular subsets and as a wide variety of tissue specific cell types, for example cardiac myocytes, islet b cells, hepatocytes and others. Mc has potential for beneficial as well as adverse consequences. Effects are likely dependent on a number of factors including i) source of the Mc ii) age of the recipient when the Mc was acquired iii) time elapsed since Mc acquisition iv) potential for interaction with other sources of Mc and v) the specific HLA molecules carried by the Mc, the recipient, and their HLA-relationship. The source of Mc and age at acquisition are relevant because maternal Mc is acquired while the immune system is developing whereas fetal Mc is acquired during adult life. Time elapsed since Mc acquisition is relevant because when a woman's children are grown, the Mc she harbors is also subject to aging i.e. is no longer fetal. HLA molecules and HLA-relationships across generations are likely of key importance. Mc is at the same time self and not self, with a broad potential across human biology. Benefits and adversity range from immunity and autoimmunity, tissue repair, cancer surveillance, and for maternal Mc, conferring instructional benefits to her newborn and as children. [ABSTRACT FROM AUTHOR]