MICROANATOMY

Detailed explanation-1: -IgG is the only maternal immunoglobulin that can cross the placenta and provide natural passive immunity to the foetus. IgG is the most abundant class of immunoglobulins in the body constituting 75% of all of them.

Detailed explanation-2: -Immunoglobulin M (IgM) does not cross the placenta; it is a result of fetal immunologic response to pathogens, an ability that is acquired early in the first trimester of pregnancy. IgG in the fetal blood at birth is a result of maternal immunoglobulin transferred across the placenta.

Detailed explanation-3: -IgG is the only antibody class that significantly crosses the human placenta. This crossing is mediated by FcRn expressed on syncytiotrophoblast cells.

Detailed explanation-4: -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.