Objective: To explore whether or not eosinophils can present antigen to T lymphocytes in vivo, and to further elucidate the process and characteristics of antigen-presentation by eosinophils in vivo.
Methods: BALB/c mice were sensitized and challenged by ovalbumin to recruit eosinophil infiltration into the airways. The airway eosinophils were purified and were labeled with a fluorescent dye. The labeled eosinophils were instilled into the mouse tracheas, fluorescent microscope was used to observe the migration of endobronchial eosinophils in vivo. Single cell suspension was prepared from paratracheal lymph nodes of mice receiving antigen-exposed eosinophil instillation, and flow cytometry was used to determine proliferation response of T cells and to identify the subset of responding T cells.
Results: By 8 h after tracheal instillation, labeled eosinophils were visible in the subcapsular region and streaming through the subcapsular sinus (19.0 +/- 1.8/mm(2)). With increasing time, the numbers of eosinophils entering the regional lymph nodes increased, peaking at 24 h (59.2 +/- 7.2/mm(2)) and persisting for at least 120 h (29.6 +/- 2.8/mm(2)). In sensitized mice that received 5 x 10(5) antigen-exposed eosinophils, in vivo percentage of proliferating T cell in the paratracheal lymph nodes 1 d after eosinophil instillation (6.9% +/- 0.5%) were much higher than basic control value (3.2% +/- 0.3%, P < 0.01), peaked at day 3 (10.8% +/- 0.8%, P < 0.01), and then declined over 7 d (6.1% +/- 0.6%, P < 0.05). Eosinophil-induced in vivo T cell proliferation was antigen-specific, and the responding T cells were limited to CD4(+) cells.
Conclusions: Eosinophils within the lumina of airways can process inhaled antigens, traffick to regional lymph nodes and function in vivo as antigen-presenting cells to stimulate responses of CD4(+) T cells.