FCER2 and chronic idiopathic urticaria: Omalizumab, an anti-IgE antibody used to treat severe allergic asthma and chronic idiopathic urticaria, binds to IgE in blood or membrane-bound on B lymphocytes, but not to IgE bound to its high (FcεRI) or low (CD23) affinity receptors in sensitized patients, which are ready to capture the allergens.