Because eosinophils recruited into the airways in allergic diseases are exposed to inhaled allergens, we evaluated whether eosinophils within the endobronchial lumen can function in vivo as antigen-presenting cells for inhaled antigens. We recovered eosinophils from the airways after aerosol antigen challenge in sensitized mice or from the peritoneal cavities of IL-5 transgenic mice and fluorescently labeled these cells ex vivo. These labeled cells, instilled intratracheally into normal mice, migrated into draining paratracheal lymph nodes and localized to T cell-rich paracortical areas. The homing of airway eosinophils to lymph nodes was not governed by eotaxin, because CCR3(-/-) and CCR3(+/+) eosinophils migrated identically. Airway eosinophils, recovered after inhalational antigen challenge in sensitized mice, expressed MHC class II and costimulatory CD80 and CD86 proteins and functioned in vitro as CD80- and CD86-dependent, antigen-specific, antigen-presenting cells. Moreover, when instilled into the airways of antigen-sensitized recipient mice, airway eosinophils recovered after inhalational antigen challenge stimulated antigen-specific CD4(+) T cell proliferation within paratracheal lymph nodes. Thus, eosinophils within the lumina of airways can process inhaled antigens, traffic to regional lymph nodes, and function in vivo as antigen-presenting cells to stimulate responses of CD4(+) T cells.