["On cross-linking of receptor-bound IgE antibodies by allergens, effector cells (basophils and mast cells) involved in type I allergic reactions degranulate and release the potent chemical mediators stored inside their granules. Total and allergen-specific IgE concentrations, IgE affinity for allergen, and IgE clonality are all distinct properties of allergic patients' IgE repertoires. However, the inability to isolate individual IgE antibodies from allergic patients' sera presents a major barrier to understanding the importance of patient-specific IgE repertoires for the manifestation and severity of allergic symptoms.", 'We sought to investigate how individual properties of an IgE repertoire affect effector cell degranulation.', 'A panel of recombinant IgE (rIgE) antibodies specific for the major house dust mite allergen Der p 2 was developed and characterized in regard to Der p 2 affinity, as well as Der p 2 epitope specificity, by using surface plasmon resonance technology. Human basophils were sensitized with different combinations of rIgEs, and degranulation responses were measured by means of flow cytometry after challenge with Der p 2.', 'A total of 31 Der p 2-specific rIgEs were produced. They bound a total of 9 different Der p 2 epitopes in the affinity range (K(D) value) of 0.0358 to 291 nM. Factors increasing human basophil degranulation were increased total IgE concentrations, increased concentrations of allergen-specific IgE relative to non-allergen-specific IgE, more even concentration of individual allergen-specific IgE clones, increased IgE affinity for allergen, and increased number of allergen epitopes recognized by the IgE repertoire (increased IgE clonality).'] Do several distinct properties of the IgE repertoire determine effector cell degranulation in response to allergen challenge?