1a)4,14. == Number 1. prevent mast cell degranulation, therefore creating the restorative potential of the HBI UNC569 design. Type I hypersensitivity (allergy) is definitely a disorder of the immune system that occurs when the adaptive immune system is directed against substances in the environment that would normally be harmless. Immediate hypersensitivity initiates when IgE antibodies bound to their high-affinity receptor (FcRI) on mast cells are cross-linked by multivalent allergens, leading to mast cell degranulation1,2. Naturally happening allergens are typically complex, structurally heterogeneous proteins, with multiple allergy-inducing epitopes. Accordingly, the IgE antibodies that are generated against these proteins are polyclonal in nature and bind their respective epitopes with a range of affinities3,4. Standard allergens possess two to twelve epitopes that are identified by polyclonal IgE antibodies58. Recent evidence suggests that among the recognized epitopes on a given allergen, only one to five are immunodominant, indicating they are involved in the degranulation response observed in the majority of patients with that particular allergy7,911. For example, the peanut allergen Ara h 3, the wheat allergen Tri a 14 and the melon allergen Cuc m 2 were each found to have four distinct epitopes triggering the allergic reaction6,12,13. Additionally, the melon allergen was found to have two high-binding and two low-binding IgE epitopes (Fig. 1a)4,14. == Number 1. Design of the HtTA and the HBI for the selective inhibition of mast cell degranulation. == (a) Structure of the melon allergen Cuc m 2 with the four recognized epitopes showing both high and low affinity for IgE antibodies. A HtTA consisting of two unique haptens UNC569 each having a valency of 2 was synthesized to model the multiple different epitopes present on a natural allergen such as Cuc m 2. To mimic the high- and low-binding IgE epitopes, the first hapten was chosen to have a high affinity and the second hapten was chosen to have a low affinity for his or her respective IgEs. (b) In an allergic reaction, the allergen binds the polyclonal IgE Igfbp5 antibodies present on the surface of mast cells. Multivalent allergen binding to surface-bound IgE antibodies cause aggregation of the IgE receptor, FcsRI, initiating a signaling cascade that results in mast cell degranulation. (c) The HtTA design mimics multiple unique epitopes as well as the polyclonal IgE response present in natural allergic reactions by using two IgE antibodies, IgE-1 and UNC569 IgE-2, each with different hapten specifcity. (d) Crystal structure of an IgG antibody with enlarged Fab UNC569 region to demonstrate the location of the nucleotide- and antigen-binding sites. The HBI was designed to simultaneously bind both the antigen- and the nucleotidebinding sites on an IgE. (e) HBI selectively inhibits the low-affinity hapten/IgE relationships, effectively decreasing the valency of the allergen rendering it incapable of causing adequate IgE cross-linking to stimulate a degranulation response. Owing to the difficulty of natural allergens, it has been a challenge to develop experimental models that mimic natural allergic responses. As a result, most allergy studies are performed using dinitrophenyl (DNP) with DNP-specific IgE (IgEDNP) as the hapten-antibody pair1519. The DNP-IgEDNPsystem uses monoclonal IgEDNPto bind the IgE receptor, FcRI, on mast cells. After the mast cells are primed with IgEDNP, cross-linking is definitely induced with DNP-conjugated synthetic allergens typically synthesized using BSA, human being serum albumin or ovalbumin as the scaffold. Despite the prevalence of this model, it has several shortcomings. First, DNP binds IgEDNPwith an atypically high affinity, which is not representative of the broad range of affinities IgEs have for natural allergy epitopes10,13,20. Second, the hapten conjugation methods used are nonspecific, resulting in heterogeneous synthetic allergens.