Human serum IgE‐mediated mast cell degranulation shows poor correlation to allergen‐specific IgE content

Background: Although allergen‐specific IgE content in serum can be determined immunochemically, little is known about the relationship between this parameter and the strength of the degranulation response upon allergen triggering. Objectives: Analyse the degranulation capacity of immunochemically defined purified and serum IgE after challenge with anti‐IgE or allergen using a rat mast cell line (RBL) transfected with the α‐chain of the human high‐affinity IgE receptor (FcɛRI). Methods: Purified IgE specific for 4‐hydroxy‐3nitrophenylacetyl, purified IgE of unknown specificity, and sera from allergic patients sensitive to Dermatophagoides pteronyssinus and Dactylis glomerata were assessed. Degranulation was measured by a β‐hexosaminidase release assay after anti‐IgE or allergen‐specific challenge. Results: For purified monoclonal IgE a significant correlation (r = 0.97) was found between the proportion of bound allergen‐specific IgE and the strength of the degranulation response. In contrast, no correlation (r = 0.27) was detected after sensitization with serum IgE. Conclusion: Our studies demonstrate that mast cell activation mediated through IgE from allergic patients is a result of complex relationships that are not only dependent on allergen‐specific IgE content but also relate to the capacity to efficiently sensitize and trigger the signalling responses that lead to degranulation.