(192) Milk Allergen-Induced Eosinophil Activation in Eosinophilic Esophagitis: The IgG4 Pathway

Introduction/Rationale: Eosinophilic esophagitis (EoE) is a chronic allergic condition, defined by symptoms of esophageal dysfunction (such as difficulty swallowing, food impactions, nausea, vomiting, etc.) and esophageal eosinophilia [15 eosinophils (Eos) per high-powered field]. Milk is the most common trigger of EoE and is known to induce disease in up to 80% of EoE patients. IgG4 is present in esophageal tissue of active EoE patients and co-localizes with food triggers and Eos-associated proteins. The mechanisms by which IgG4 contributes to allergic inflammation in EoE, however, remain unclear.

Methods: A peripheral blood sample from an active EoE patient was used to generate food allergen-specific IgG4 monoclonal antibodies (mAbs). Solid-phase immune complexes (ICs) were formed by incubating these IgG4 mAbs (Bos d 8-specific) with Bos d 8-coated ELISA plates and soluble ICs were formed by mixing IgG4 mAbs with Bos d 8 in solution before incubating with eosinophils (Eos). Eos were isolated from the peripheral blood of mildly allergic volunteers using Miltenyi magnetic separation and incubated with ICs for 1 hour. Eos activation was determined by quantifying Eos-derived neurotoxin (EDN) release in culture supernatants.

Results: Bos d8-specific IgG4 mAbs were successfully generated from antibody-secreting B cells of active EoE patients using the hybridoma technique. Naïve Eos incubated with solid-phase IgG4-Bos d 8 ICs released significantly more EDN compared to Eos incubated with IgG4 alone (477.3 ± 28.1 vs 243.5 ± 8.8, p < 0.01) in a dose-dependent manner. Moreover, Eos pre-treated with Fc-blocker did not show activation upon subsequent incubation with the IgG4-Bos d 8 ICs (278.3 ± 21.3 vs 307.57 ± 7.3). Interestingly, Eos incubated with soluble ICs did not show any activation.

Conclusion: These findings suggest that the solid phase IgG4-Bos d 8 ICs activate Eos via an Fc-gamma receptor. Further research is needed to confirm whether this process occurs in EoE patients.