Final answer:
The order of placental transfer efficiency for IgG subclasses, from most to least, is typically IgG1, IgG3, IgG4, and IgG2. IgG provides passive immunity by crossing the placental barrier, and IgA contributes to postnatal immunity through breastfeeding.
Step-by-step explanation:
The efficiency of placental transfer for IgG subclasses varies, with some able to cross more efficiently than others. Typically, studies suggest the order from most to least efficient in crossing the placenta aligns somewhat with the subclasses' serum concentrations: IgG1 > IgG3 > IgG4 > IgG2. Immunoglobulin G (IgG) is the most versatile class of antibody and the only class able to cross the placental barrier, thereby providing passive immunity to the fetus. This transport is crucial for protecting the developing fetus from infections.
During pregnancy, the placental transfer of IgG is an essential aspect of natural passive immunity. It allows the developing fetus to gain protection against pathogens based on the mother's immunological history. Post-birth, newborns continue to receive immunity through breast milk, which contains secretory IgA.