Murine Airway Eosinophils Preferentially Induce T Helper Cell Type 2 Differentiation

Objective : Eosinophils express MHC class II molecules and costimulatory molecules,and function as antigen-presenting cells(APCs) to stimulate the proliferation of antigen(Ag)-specific CD4+ T lymphocytes both in vitro and in vivo. In this investigation,we evaluated whether eosinophils within the tracheobronchial lumen can stimulate Th2 cell expansion by presenting Ag.Methods: (1) BALB/c mice were sensitized intraperitoneally with ovalbumin(OVA),then sensitized mice underwent inhalational challenges with the same antigen to obtain bronchoalveolar lavage fluid(BALF) for eosinophil purification.In vitro,purified BALF eosinophils from BALB/c mice were incubated with purified CD4+ T cells separated from spleens.Cultures were incubated for 96h at 37 in a 5% CO2 humidified atmosphere.Cell-free culture supernatants were collected and stored in aliquots at -70 before analysis of IL-4,IL-5,IL-13,and IFN- .(2) In vivo,purified OVA-exposed eosinophils were instilled slowly into trachea.At 3 days thereafter,the draining paratracheal lymph nodes were removed and teased into cell suspension.Lymph node cells were cultured for 48h before collection of the cell-free culture supernatants for Thl/Th2 cytokines analysis. We use anti-CD80 and/or anti-CD86 monoclonal antibodies as controls both in vitro and in vivo.Results: (1) Our data showed the airway eosinophils which were recovered following inhalational OVA challenge in sensitized mice functioned as CD80- and CD86-dependent APCs for stimulating sensitizedCD4+ lymphocytes to produce interleukin (IL)-4,IL-5 and IL-13, but not interferon- (IFN- ) in in vitro assay.(2) When instilled intratracheally in OVA-sensitized recipient mice,these Ag-loaded eosinophials migrated into draining paratracheal lymph nodes primed Th2 cells in vivo for IL-4,IL-5 and IL-13,but not for IFN- . Anti-CD80 and -CD86 mAbs can highly suppress the production of Th2 type cytokines both in vitro and in vivo assay.This suggested that the process of Th2 cell differentiation was CD80-and CD86-dependent.Conclusions: We concluded that eosinophils within the lumina of airways could process inhaled Ags function in vitro and in vivo as APCs to promote expansion of Th2 cells.This investigation highlights the potential of eosinophils to not only act as terminal effector cells but also to actively modulate immune responses by amplifying Th2 cell responses.