Exchange of fetal and maternal cells is common in all pregnancies. But there is an increased level of immune complexes in the serum of male newborns than in females. Why these differences occur?
Some fetal cells express cell surface markers, or antigens, that originate from the father. Under normal circumstances, the mother's immune system would recognize these as foreign and attack the cells.
Regulatory T cells (Tregs), which are a specialized form of white blood cell that promote an anti-inflammatory environment, actively protect such fetal cells.