Which immunoglobulin has the shortest half-life due to poor binding to FcRn?

Immunoglobulin G (IgG) is known for its relatively long half-life in circulation, primarily due to its ability to effectively bind to the neonatal Fc receptor (FcRn). This binding protects IgG from degradation, allowing it to persist longer in the bloodstream. However, among the various subclasses of IgG, IgG3 is unique in having the shortest half-life.

The short half-life of IgG3 is mainly attributed to its lower affinity for FcRn compared to other IgG subclasses like IgG1 and IgG2. Since FcRn plays a crucial role in recycling IgG and preventing its degradation, IgG3 does not benefit as much from this protective mechanism. As a result, it is cleared from the serum more quickly than other IgG subclasses.

This distinction makes IgG3 the correct answer in the context of which immunoglobulin has the shortest half-life due to its poor binding characteristics to FcRn, leading to less effective protection against catabolism.