Why do not maternal antibodies attack the fetus?

Maternal antibodies do not typically attack the fetus because of several mechanisms that prevent immune rejection during pregnancy. These mechanisms include:

Placental barrier: The placenta, which develops during pregnancy, acts as a physical barrier between the maternal and fetal circulatory systems. It allows the exchange of nutrients, oxygen, and waste products while preventing the direct mixing of maternal and fetal blood. The placenta also produces various hormones and factors that suppress maternal immune responses against the fetus.

Immunological tolerance: The mother's immune system develops immunological tolerance to the fetus during pregnancy. This is achieved through several mechanisms, including the production of blocking antibodies (IgG) that neutralize potentially harmful maternal antibodies and the regulation of immune cells at the maternal-fetal interface.

Antigenic similarity: The fetus inherits antigens (markers on cell surfaces) from both the mother and the father. Some of these antigens may be similar to those of the mother, which helps prevent her immune system from recognizing the fetus as foreign.

Fetal antigens: The fetus expresses unique antigens (trophoblast-specific antigens) that are not present in the mother's tissues. These antigens are recognized by the maternal immune system, but the immune response is usually modulated to avoid harming the fetus.

Regulatory immune cells: Certain immune cells, such as regulatory T cells (Tregs), play a role in suppressing immune responses against the fetus. Tregs help maintain immune balance and prevent excessive immune reactions.

Despite these protective mechanisms, there can still be instances of immune incompatibility between the mother and the fetus, which can lead to conditions like Rh incompatibility or immune-mediated pregnancy complications. However, the mechanisms mentioned above generally ensure that maternal antibodies do not attack the fetus during a healthy pregnancy.