HLA-DQA1 and peanut allergic reaction: Since IgG4 serves as a blocking antibody limiting the interaction of peanut allergen with IgE on the surface of mast cells and basophils (13), our findings in LEAP would imply that individuals with the HLA-DQA1*01:02 allele present particular peanut allergenic peptides (i.e., Ara h 2) for immune recognition that invokes protective mechanisms when introduced to the diet prior to the development of peanut allergy.