FCER2 and Allergy: However, in the context of allergy, receptor-mediated internalization of allergen-IgE complexes via high (FcεRI) affinity (Figure 2B) and low (CD23) affinity (Figure 2C) receptors for IgE by APCs- a process called facilitated antigen presentation (FAP)—has been shown to stimulate allergen-specific T cell proliferation more efficiently, in particular at low concentrations of allergen as they occur in vivo in allergic patients (6, 57–60).