Which IgG subclass is most efficient at crossing the placenta?

The efficient transfer of immunoglobulin G (IgG) subclasses across the placenta is a crucial mechanism in providing passive immunity to the fetus during pregnancy. Among the IgG subclasses, IgG1 is recognized as the most effective at crossing the placenta. This efficiency is largely attributed to the structure of the IgG1 molecule as well as its affinity for the FcRn (neonatal Fc receptor), which plays a significant role in the transport of maternal antibodies across the placental barrier.

The FcRn receptor binds to IgG1 during pregnancy, allowing it to be taken up from maternal circulation and transferred to the fetal bloodstream. This transplacental movement helps to ensure that the developing fetus receives antibodies that can offer protection against infections.

While the other subclasses, IgG2, IgG3, and IgG4, also have some ability to cross the placenta, they do so with significantly less efficiency than IgG1. IgG2 is less efficient because it interacts less favorably with the FcRn receptor compared to IgG1. IgG3, while having a structure that allows for strong immune responses, is also less effectively transferred due to its larger size and propensity to form larger complexes, which hinder passage. IgG4, on the