Migration and accumulation of eosinophils toward regional lymph nodes after airway allergen challenge

Background: Eosinophils play a major role in allergic airway inflammation because of their ability to release toxic mediators. In addition, they are able to migrate toward draining thoracic lymph nodes (TLNs) after intratracheal administration, where they can function as antigen-presenting cells. Objective: In this study, we evaluated in vivo eosinophil migration toward the TLN after allergen sensitization and analyzed expression of molecules involved in antigen presentation. Methods: Mice were sensitized by intraperitoneal injection of ovalbumin on days 1 and 10 and challenged once intranasally with ovalbumin on day 20. The kinetics of eosinophilia was evaluated in blood, lung tissue homogenate, bronchoalveolar lavage fluid, and TLN. Cell surface staining was analyzed by flow cytometry. Results: The kinetics of eosinophil recruitment was similar in TLN, lung tissue, and blood, beginning at 12 hours and peaking at 48 hours after allergen challenge. Approximately 70% of TLN eosinophils expressed MHC class II molecules, compared with less than 25% in blood and lungs. Moreover, TLN eosinophils expressed higher levels of MHC class II and CD86 compared with blood and lung eosinophils. Most eosinophils expressed CD80 and CD54, whereas only a few eosinophils expressed CD40. Eosinophils in lungs and TLN appeared to be activated with lower CD62-ligand expression compared with blood eosinophils. Conclusion: The presence of eosinophils with a different phenotype in the TLN at early time points after allergen challenge of sensitized mice supports their capacity to serve as antigen-presenting cells, sustaining allergic/inflammatory responses in the airways.