Allergen-specific immunotherapy (SIT) leads to a long-term amelioration of IgE-and Th2-mediated allergic diseases. However, SIT efficiency is low, with years of treatment along with frequent allergic side effects. The goal of this study was to reduce the side effects by destroying IgE-binding epitopes, i.e. by heat-denaturation, while preserving the therapeutic effect. Mice were immunised with bee venom, birch pollen, grass pollen or cat hair allergens, or with ovalbumin. Heat-denatured allergens bound less IgE but enhanced Th1-dependent IgG2a production as measured by ELISA. The strong IgG2a antibody responses also prevented allergic anaphylaxis in mice, as measured by body temperature drop after a challenge with a high allergen dose. We found that optimal heat-denaturation of allergens left a small proportion in the native conformation to sufficiently stimulate B cells, while non-B cell-mediated effects were probably amplified. The enhanced immunogenicity of heat-denatured allergens is likely explained by enhanced antigen presentation to T cells due to the particulate nature of heat-denatured proteins. This enables Th1 skewing of the immune response with strong production of IgG2a in mice. Therefore, heat-denaturation represents probably the simplest way to enhance the efficiency of SIT while reducing its side effects.
IntroductionIgE-mediated type I hypersensitivity is characterised by prominent activity of mast cells, eosinophils, T helper type 2 (Th2) cells and cytokine actions. Allergenspecific immunotherapy (SIT) leads to long-term amelioration of allergic symptoms and is therefore recommended as a first-line therapy for allergies [1]. During SIT, gradually increasing allergen doses are subcutaneously administered until a maintenance dose is reached, and then treatment continues for 3-5 years. Such lengthy treatment, requiring 30-80 allergen injections, is very costly [2]. Also, SIT frequently causes adverse events due to the interaction of specific IgE with the injected allergen. These adverse events frequently include a local reaction at the site of allergen injection, but also life-threatening systemic reactions such as asthma and anaphylaxis. This is why the administered allergen doses must be kept relatively low, which unfortunately favours Th2 immune responses in contrast to higher doses [3][4][5].Several strategies have been developed to tackle the problems of SIT, i.e. to reduce its side effects and to enhance its immunogenicity. One strategy is to replace the currently used aluminium salts, which have Th2-polarizing properties, with novel adjuvants such as Tolllike receptor ligands [6,7] that trigger Th1 responses. Another strategy is to increase safety and tolerability of SIT by injecting the allergen in a form that is not recognised by IgE, such as naked DNA vaccines Heat-denaturation is well known to reduce the reactogenicity of allergens with IgE, as cooked foods are usually well or better tolerated by allergic individuals [24][25][26]. In this study, we tested whether this very simple strate...
