The bell-shaped dose-response
The typical BAT result in allergic patients is a bell-shaped curve for the %CD63-positive basophils with increasing concentrations of allergen. As the antigen-specific IgE-FcεRI complex is a receptor aggregation reaction that depends on the affinity of IgE for the allergen and on the valency of the allergen, a dose-response curve is often bell-shaped. However, the complexity of antigens and the relative affinity of different epitopes on allergens for profiles of epitope-specific IgE (bound to the cell) of different patients results in dose-response curves that vary in form. As can be seen from the variability shown by the different dose-response curves, tests with single concentrations of antigen can be misleading. There are a number of factors that can impact the dose response curves of basophil surface activation markers such as affinity of the antigen for the IgE, epitope spreading of the IgE antibody, the density of the epitope-specific IgE on the cell surface, and an intrinsic characteristic of the basophil itself. The combination of these factors determines the optimal allergen concentration for basophil activation, thus this point might vary significantly among subjects and between different allergens in the same subject. 19,20. Therefore, it is preferable to include a broad range of allergen concentrations to better appreciate the effect of the allergen on basophil response.