Hunt James, Bracher Marguerite G, Shi Jianguo, Fleury Sébastien, Dombrowicz David, Gould Hannah J, Sutton Brian J, Beavil Andrew J
King's College London, Medical Research Council, Randall Division of Cell and Molecular Biophysics, Guy's Campus, London SE1 1UL, United Kingdom.
J Biol Chem. 2008 Oct 31;283(44):29882-7. doi: 10.1074/jbc.M804742200. Epub 2008 Aug 13.
The high affinity of IgE for its receptor, FcepsilonRI (K(a) approximately 10(10) M(-1)), is responsible for the persistence of mast cell sensitization. Cross-linking of FcepsilonRI-bound IgE by multivalent allergen leads to cellular activation and release of pro-inflammatory mediators responsible for the symptoms of allergic disease. We previously demonstrated that limiting the IgE-FcepsilonRI interaction to just one of the two Cepsilon3 domains in IgE-Fc, which together constitute the high affinity binding site, results in 1000-fold reduced affinity. Such attenuation, effected by a small molecule binding to part of the IgE:FcepsilonRI interface or a distant allosteric site, rather than complete blocking of the interaction, may represent a viable approach to the treatment of allergic disease. However, the degree to which the interaction would need to be disrupted is unclear, because the importance of high affinity for immediate hypersensitivity has never been investigated. We have incorporated into human IgE a mutation, R334S, previously characterized in IgE-Fc, which reduces its affinity for FcepsilonRI approximately 50-fold. We have compared the ability of wild type and R334S IgE to stimulate allergen-induced mast cell activation in vitro and in vivo. We confirmed the expected difference in affinity between wild type and mutant IgE for FcepsilonRI (approximately 50-fold) and found that, in vitro, mast cell degranulation was reduced proportionately. The effect in vivo was also marked, with a 75% reduction in the passive cutaneous anaphylaxis response. We have therefore demonstrated that the high affinity of IgE for FcepsilonRI is critical to the allergic response, and that even moderate attenuation of this affinity has a substantial effect in vivo.
IgE对其受体FcepsilonRI具有高亲和力（解离常数Ka约为10¹⁰ M⁻¹），这导致肥大细胞致敏持续存在。多价变应原使结合在FcepsilonRI上的IgE发生交联，从而导致细胞活化并释放促炎介质，这些介质是过敏性疾病症状的起因。我们之前证明，将IgE-Fc中两个共同构成高亲和力结合位点的Cepsilon3结构域之一中的IgE-FcepsilonRI相互作用限制起来，会使亲和力降低1000倍。这种减弱是由小分子与IgE:FcepsilonRI界面的一部分或远处的别构位点结合引起的，而不是完全阻断相互作用，这可能是一种治疗过敏性疾病的可行方法。然而，尚不清楚相互作用需要被破坏到何种程度，因为从未研究过高亲和力对速发型超敏反应的重要性。我们已将先前在IgE-Fc中鉴定出的R334S突变引入人IgE中，该突变使其对FcepsilonRI的亲和力降低了约50倍。我们比较了野生型和R334S IgE在体外和体内刺激变应原诱导的肥大细胞活化的能力。我们证实了野生型和突变型IgE对FcepsilonRI的亲和力存在预期差异（约50倍），并发现体外肥大细胞脱颗粒相应减少。体内效果也很显著，被动皮肤过敏反应降低了75%。因此，我们证明了IgE对FcepsilonRI的高亲和力对过敏反应至关重要，而且即使这种亲和力适度减弱在体内也有显著效果。
