The mechanism by which IgG4 exerts a protective role in allergic disease clearly merits further investigation, and it is important to note that of all IgG subclasses, IgG4 has the highest affinity for the inhibitory receptor FcγRIIb (98), which could have implications for the inhibition of mast cell/basophil activation. This evidence concerns the gene FCGR2B and allergic disease.