Further, in addition to mast cells, eosinophils activated by the same Fel d1/IgE complexes contribute to allergy pathogenesis by producing lager amounts of leukotrienes (LTC4, LTD4, and LTE4) and platelet-activating factor (PAF), pro-inflammatory lipids that induce local vasodilatation, edema, neurogenic stimulation, smooth muscle contraction and hypersecretion of mucus (19). The gene discussed is IGHE; the disease is allergic disease.