Blockade of peanut allergy with a novel Ara h 2-Fcγ fusion protein in mice.

BACKGROUND: Conventional immunotherapy for peanut allergy using crude peanut extracts is not recommended because of the unacceptably high risk of anaphylaxis. Allergen-specific immunotherapy is not currently undertaken for peanut allergy. OBJECTIVES: The objective of this study was to develop a novel peanut-human fusion protein to block peanut-induced anaphylaxis. METHODS: We genetically designed and expressed a novel plant-human fusion protein composed of the major peanut allergen Ara h 2 and human IgG Fcγ1. We tested the Ara h 2-Fcγ fusion protein (AHG2)'s function in purified human basophils. Transgenic mice expressing human FcεRIα and a murine peanut allergy model were used. RESULTS: AHG2 inhibited histamine release induced by whole peanut extract (WPE) from basophils of patients with peanut allergy, whereas the fusion protein itself did not induce mediator release. AHG2 inhibited the WPE-induced, peanut-specific, IgE-mediated passive cutaneous anaphylaxis in hFcεRIα transgenic mice. AHG2 also significantly inhibited acute anaphylactic reactivity, including the prototypical decrease in body temperature in WPE-sensitized mice challenged with crude peanut extract. Histologic evaluation of the airways showed that AHG2 decreased peanut-induced inflammation, whereas the fusion protein itself did not induce airway inflammation in peanut-sensitized mice. AHG2 did not exert an inhibitory effect in mice lacking FcγRII. CONCLUSION: AHG2 inhibited peanut-specific IgE-mediated allergic reactions in vitro and in vivo. Linking specific peanut allergen to Fcγ can provide a new approach for the allergen immunotherapy of peanut allergy.

Role of complement in a murine model of peanut-induced anaphylaxis.

Peanut allergy is severe and persisting from childhood to adulthood. However, there is no effective prophylaxis or treatment for peanut allergy. Little is known to about the molecular process in the pathogenesis of peanuts allergy, especially in innate immunity. Thus we investigated the role of complement activation in murine peanut anaphylaxis. Complement component C3 deposition on peanut extract (PE) was evaluated using sera from wild-type (WT), mannose-binding lectin associated serine protease (MASP)-1/3 deficient, MASP-2 deficient, and C4 deficient mice. Sera from interferon regulatory factor-4 (IRF-4) deficient mice, which lack serum immunoglobulin, were also used. In anaphylaxis study, mice were pretreated with propranolol and a long-acting form of IL-4, and injected with PE. Mice were then assessed for plasma C3a levels and hypothermia shock by ELISA and rectal temperature measurement, respectively. C3 deposition on PE was abolished in immunoglobulin- and C4-deficient sera. No difference in C3 deposition levels were observed among WT, MASP-1/3 deficient and MASP-2 deficient sera. IgM, IgG2b, IgG3, C1q, and ficolin-A deposits were detected on PE. In anaphylaxis study, MASP-1/3 deficient mice showed elevation of plasma C3a levels similar to WT mice. However, they were significantly reduced in C4- and MASP-2-deficient mice compared to WT mice. Consistently, PE-induced anaphylactic shock was prevented in C4 deficient mice and partially in MASP-2 deficient mice. In conclusion, PE activates complement via both the lectin and classical pathways in vivo, and the complement activation contributes to hypothermia shock in mice.