Neutrophil oxidative burst as a diagnostic indicator of IgG-mediated anaphylaxis.

Background: IgG-mediated anaphylaxis occurs after infusion of certain monoclonal antibody-based therapeutics. New in vitro tests are urgently needed to diagnose such reactions. We investigated whether allergens trigger neutrophil oxidative burst (OB) and if neutrophil OB occurs due to allergen-specific IgG (sIgG).

Methods: Neutrophil OB was measured by dihydrorhodamine 123 flow cytometry using a leukocyte suspension spiked with a very small patch of the allergen crude extract, Dermatophagoides farinae ( Der f ). The mean fluorescence intensity ratio of stimulated to unstimulated samples was calculated as the neutrophil oxidative index (NOI).

Results: The Der f -specific NOI ( Der f -sNOI) showed a time-dependent increase after Der f extract addition. At 15 min activation, higher Der f -sIgG levels were associated with lower Der f -sNOI values in 31 subjects ( P <0.05). This inverse relationship occurs due to the initial blocking effect of free Der f -sIgG. Additionally, neutrophil OB was nearly absent ( Der f -sNOI of -1) in two cases: a subject with undetectable Der f -sIgG levels and washed leukocyte suspensions deprived of Der f -sIgG.

Conclusion: Allergens can trigger neutrophil OB via preexisting allergen-sIgG. Neutrophil OB can be easily measured in a leukocyte suspension spiked with the allergen. This assay can be used to diagnose IgG-mediated anaphylaxis.