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.