Do Mobile Eosinophil Progenitors Contribute to Eosinophilia in the Allergic Lung?
In response to inflammatory signals in the lung, eosinopoiesis occurs in the bone marrow, and mature eosinophils migrate from this compartment via the blood to the bronchial mucosa, where they receive specific signals to release a range of proinflammatory mediators that drive pathogenesis (1, 3). However, evidence is also accumulating for an extramedullary role of eosinophil progenitor cells in the pathogenesis of allergic disease (5, 28). An emerging hypothesis is that communication between the lung and bone marrow compartments in response to allergen provocation upregulates the production of eosinophil progenitors in the bone marrow. These IL-5-responsive cells then undergo differentiation in the bone marrow or migrate to the allergic lung. Cytokines elaborated from resident inflammatory and airway cells then locally drive differentiation of these lineage-committed progenitor cells to mature effector cells. Thus, two mechanisms may operate to promote eosinophilia during allergic resp
