Asam C, Batista A L, Moraes A H, de Paula V S, Almeida F C L, Aglas L, Kitzmüller C, Bohle B, Ebner C, Ferreira F, Wallner M, Valente A P
Christian Doppler Laboratory for Allergy Diagnosis and Therapy, University of Salzburg, Salzburg, Austria.
Clin Exp Allergy. 2014 Aug;44(8):1083-93. doi: 10.1111/cea.12361.
Birch pollen allergy represents the main cause of winter and spring pollinosis in the temperate climate zone of the northern hemisphere and sensitization towards Bet v 1, the major birch pollen allergen, affects over 100 million allergic patients. The major birch pollen allergen Bet v 1 has been described as promiscuous acceptor for a wide variety of hydrophobic ligands.
In search of intrinsic properties of Bet v 1, which account responsible for the high allergenic potential of the protein, we thought to investigate the effects of ligand-binding on immunogenic as well as allergenic properties.
As surrogate ligand of Bet v 1 sodium deoxycholate (DOC) was selected. Recombinant and natural Bet v 1 were characterised physico-chemically as well as immunologically in the presence or absence of DOC, and an animal model of allergic sensitization was established. Moreover, human IgE binding to Bet v 1 was analysed by nuclear magnetic resonance (NMR) spectroscopy.
Ligand-binding had an overall stabilizing effect on Bet v 1. This translated in a Th2 skewing of the immune response in a mouse model. Analyses of human IgE binding on Bet v 1 in mediator release assays revealed that ligand-bound allergen-induced degranulation at lower concentrations; however, in basophil activation tests with human basophils ligand-binding did not show this effect. For the first time, human IgE epitopes on Bet v 1 were determined using antibodies isolated from patients' sera. The IgE epitope mapping of Bet v 1 demonstrated the presence of multiple binding regions.
Deoxycholate binding stabilizes conformational IgE epitopes on Bet v 1; however, the epitopes themselves remain unaltered. Therefore, we speculate that humans are exposed to both ligand-bound and free Bet v 1 during sensitization, disclosing the ligand-binding cavity of the allergen as key structural element.
桦树花粉过敏是北半球温带气候区冬春季节花粉症的主要原因，对主要桦树花粉过敏原Bet v 1致敏影响超过1亿过敏患者。主要桦树花粉过敏原Bet v 1被描述为多种疏水配体的混杂受体。
为寻找Bet v 1的内在特性，其是该蛋白高致敏潜力的原因，我们想研究配体结合对免疫原性和致敏特性的影响。
选择脱氧胆酸钠（DOC）作为Bet v 1的替代配体。在有或无DOC存在的情况下，对重组和天然Bet v 1进行物理化学及免疫学表征，并建立过敏致敏动物模型。此外，通过核磁共振（NMR）光谱分析人IgE与Bet v 1的结合。
配体结合对Bet v 1具有整体稳定作用。这在小鼠模型中转化为免疫反应的Th2偏向。在介质释放试验中对人IgE与Bet v 1结合的分析表明，配体结合的过敏原在较低浓度下诱导脱颗粒；然而，在用人嗜碱性粒细胞进行的嗜碱性粒细胞活化试验中，配体结合未显示此效应。首次使用从患者血清中分离的抗体确定了Bet v 1上的人IgE表位。Bet v 1的IgE表位图谱证明存在多个结合区域。
脱氧胆酸盐结合稳定了Bet v 1上的构象性IgE表位；然而，表位本身保持不变。因此，我们推测人类在致敏过程中同时接触配体结合型和游离型Bet v 1，揭示过敏原的配体结合腔作为关键结构元件。
