Given the correlation of aeroallergen-specific IgG levels both with protection from allergic symptoms in IgE-sensitized individuals and with the suppression of asthma and rhinitis in subjects receiving immunotherapy, we hypothesized that anti-inflammatory effects of IgG, exerted via FcγRIIb, might suppress an airway inflammatory response to aeroallergens in a pathway orchestrated specifically by mast cells. This evidence concerns the gene FCGR2B and asthma.