Fetal and neonatal allo-immune response.

The components of the immune system may be present in early stages of embryonic and then fetal, then they reach maturity at different stages of pregnancy. Just as the growth and development of the components of the embryonic and then fetal immune system progressively mature, functions are acquired sequentially during the course of pregnancy, both the ability to mount a cell-mediated or antibody-mediated immune response and the tolerance towards a certain group of antigens. The fetus is immunocompetent because during this development, it acquires the ability to generate an immune response. As development takes place, the fetus also generates specific tolerance as it is exposed to genetically foreign and non-inherited maternal antigens. Nonetheless, the fetal immune system does not attack nor harm maternal tissues. At birth, the immune system, although developed, is not mature enough yet. Furthermore, passive transfer of maternal antibodies creates a unique scenario of compatibility that cannot be seen in children or adults. Recent advances in knowledge of fetal and neonatal immunology make it possible to recognize the risks associated with transfusion and how to resolve them.