IMMUNOLOGY

Detailed explanation-1: -IgG is the only antibody class that significantly crosses the human placenta. This crossing is mediated by FcRn expressed on syncytiotrophoblast cells.

Detailed explanation-2: -The efficiency of transplacental transfer of the different IgG subclasses was determined. Transfer of IgG1 and IgG4 was found to be significantly more efficient than that of IgG3 and IgG2. IgG2 was the subclass least efficiently transferred from mother to fetus.

Detailed explanation-3: -Erythroblastosis fetalis is hemolytic anemia in the fetus caused by transplacental transmission of maternal antibodies to fetal red blood cells, usually due to incompatibility between maternal and fetal blood groups, often Rho(D) antigens.