Published online: April 4, 2020
In atopy-prone individuals, inhalation of the major birch pollen allergen Bet v 1 induces the production of specific IgE antibodies which cause birch pollinosis. A portion of these IgE antibodies binds to the major allergen in apple, Mal d 1, because it has the same structure as Bet v 1. This cross-reactivity induces birch pollen-related apple allergy in up to 70 % of birch pollen-allergic individuals. Consequently, birch pollen-related apple allergy represents the most abundant food allergy in adults, adolescents and also affects children. Although the symptoms are mainly confined to the oral cavity, birch pollen-related food allergy often appears perennially and impairs the quality of life of the affected individuals.
Birch pollinosis can be effectively treated by specific immunotherapy with birch pollen. Contrary to expectations, the efficacy of birch pollen immunotherapy on the related apple allergy is limited. Recently, a double-blind placebo-controlled study revealed that sublingual immunotherapy (SLIT) with Mal d 1 significantly ameliorated birch pollen-related apple allergy, whereas SLIT with Bet v 1 did not. To elucidate the immune mechanism underlying this finding, Sánchez Acosta and colleagues studied the Mal d 1-specific antibody response in sera from individuals who received Mal d 1- and Bet v 1-SLIT, respectively. To this aim, they compared the quantity, specificity and IgE-blocking activity of Mal d 1-specific IgG antibodies published in The Journal of Allergy & Clinical Immunology (JACI).
The levels of Mal d 1-specific IgG antibodies after both treatments were comparable. Yet, their ability to inhibit IgE-induced allergic reactions differed significantly among both groups. Solely antibodies following Mal d 1-SLIT blocked IgE-mediated reactions to the apple allergen indicating that they are IgE-blocking IgG antibodies. As possible explanation for this phenomenon Sánchez Acosta and colleagues found a discrepancy in the specificity of Mal d 1-reactive IgG antibodies in either group. IgG antibodies induced by Mal d 1-SLIT bound to regions exclusively present on the surface of the apple allergen whereas IgG antibodies induced by Bet v 1-SLIT recognized epitopes shared by Bet v 1 and Mal d 1.
SLIT with Mal d 1 improved birch pollen-related apple allergy and induced protective Mal d 1-specific IgG antibodies. The limited induction of IgE-blocking antibodies by SLIT with Bet v 1 provides one explanation for the low efficacy of immunotherapy with birch pollen on birch pollen-related food allergy. This information is relevant for future therapeutic developments for this common food allergy.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.