Advanced Topics in Genetics

MicrochimerismMajor reference: J.L. Nelson, “Your Cells Are My Cells,”

Scientific American, Feb. 2008

Chimera

In Greek mythology, a creature composed of parts of a lion, goat, and snake.

Advanced Topics in Genetics: Micochimerism

• Definition: a situation in which an individual has a small number of cells that arose from a different individual• These cells are genetically distinct

from the host.

Micochimerism• The most common type arises during

pregnancy.• A few cells can cross from the mother to

the fetus, and from the fetus to the mother. (When did we hear about this before?)

• If these are stem cells, they may be able to grow and persist in the other individual.

Detection of Micochimerism

• Microchimerism is most obvious when the sexes of the individuals differ

• What would be an obvious microscopic difference for female cells in a male?

• For male cells in a female?

Micochimerism

• Another type arises from organ transplant or blood donation.• The donated tissue may contain

stem cells that migrate to another part of the recipient body and reproduce.

Micochimerism

• A third type arises from exchange of cells between twins.• There may also be cells obtained from

a “vanished twin” that was lost early in pregnancy.• Some evidence for transfer from

mother to child during breast feeding.

Micochimerism: How Much?

• Some studies suggest we all contain some microchimeric cells from our mothers.• All mothers may have some

microchimeric cells from their children.• May amount to about 1 in 1000 cells.

Micochimerism: Role in Disease

• Because they may have some distinct antigens, microchimeric cells might be attacked by the immune system.• This could lead to damage of the

person’s tissues.• Autoimmune disease – a disease in

which the person’s immune system attacks his or her own tissues.

Micochimerism: Role in Disease

• There is evidence that microchimerism is involved in at least some cases of these autoimmune diseases:–Scleroderma (results in thickening of

skin and other damage)–Systemic lupus erythematosus (many

organs are attacked)

http://www.scleroderma.org/images/SD_Images/images/scleroderma-hand_jpg.jpg

http://www.humanillnesses.com/original/images/hdc_0001_0001_0_img0066.jpg