Endobronchial eosinophils preferentially stimulate T helper cell type 2 responses

Background: Antigen‐loaded eosinophils instilled intratracheally into mice were capable of migrating into local lymph nodes and localize to the T cell‐rich paracortical zones where they stimulated antigen‐specific proliferation of CD4+ T cells. The aim of the present study was to evaluate whether eosinophils within the tracheobronchial lumen can stimulate Th2 cell expansion by presenting antigen both in vitro and in vivo. Methods: Airway eosinophils were recovered from ovalbumin‐sensitized and ‐challenged BALB/c mice, these eosinophils were then co‐cultured with sensitized CD4+ cells in the absence or presence of anti‐CD80 or/and ‐CD86 monoclonal antibodies. Airway eosinophils were instilled into the trachea of sensitized mice. At 3 days thereafter, the draining paratracheal lymph nodes were removed and teased into cell suspensions for culture. Cell‐free culture supernatants were collected for detection of cytokines. Results: Our data showed that airway eosinophils functioned as CD80‐ and CD86‐dependent antigen‐presenting cells (APCs) to stimulate sensitized CD4+ lymphocytes to produce interleukin (IL)‐4, IL‐5, and IL‐13, but not interferon (IFN)‐γ in in vitro assay. When instilled intratracheally in sensitized recipient mice, airway eosinophils migrated into draining paratracheal lymph nodes primed Th2 cells in vivo for IL‐4, IL‐5, and IL‐13, but not IFN‐γ, production during the in vitro culture that was also CD80‐ and CD86‐dependent. Conclusion: Eosinophils within the lumina of airways could process inhaled antigen 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.