The facilitated antigen binding (FAB) assay--a protocol to measure allergen-specific inhibitory antibody activity.

Specific allergen immunotherapy is an effective treatment for IgE-mediated allergic disease and involves T- and B-cell mediated events. IgE receptors on the surface of antigen-presenting cells facilitate the presentation of allergens in the presence of specific IgE antibody resulting in T-cell activation. Interference with these IgE-dependent mechanisms by 'blocking' IgG antibodies may downregulate T-cell responses and manifest as a reduction in allergic responses in vivo. The vigor of proliferative responses by T-cell clones is representative of the binding of allergen-IgE complexes to B cells. Therefore, a simplified assay can be employed that measures the binding of allergen-IgE complexes to B cells instead of a more complex assay involving proliferative assays using antigen-specific T-cell clones. Allergen-IgE complexes can be easily detected by flow cytometry and this simplified technique is called the IgE-facilitated allergen binding (IgE-FAB) assay which is described in this chapter.