Mast Cell Progenitor Trafficking in Allergic Airway Inflammation

Mast cell progenitors originate from the bone marrow and migrate to the lungs via the blood. During maturation, these cells acquire granules that contain a potent array of bronchoconstrictive mediators. The number of pulmonary mast cells is augmented in asthmatic patients and in mice with allergic airway inflammation, possibly contributing to airway hyperreactivity. An increase in mast cells is likely due to an increased recruitment of committed mast cell progenitors from the blood. However, until now a committed mast cell progenitor population has not been found in adult peripheral blood. We isolated Lin- c-kithi ST2+ integrin β7hi CD16/32hi progenitors from murine blood and showed that these cells were committed to the mast cell lineage. Based on the expression of FcεRI, these cells were less mature in Th1-prone C57BL/6 mice than in Th2-prone BALB/c mice. Asthma is associated with elevated levels of IgE. Upon exposure to allergens, IgE immune complexes are formed. In a mouse model of allergic airway inflammation, we showed that intranasal administration of IgE immune complexes to antigen-sensitized mice resulted in an increased number of mast cell progenitors compared with antigen administration alone. The increase in mast cell progenitors was independent of the low-affinity IgE receptor CD23. Rather, signaling through the common FcRγ-chain was required to enhance the number of lung mast cell progenitors. Signaling through FcεRI was likely responsible for the increase. However a role for FcγRIV could not be excluded. CD11c+ cells, such as dendritic cells, are important for antigen sensitization. In a mouse model of allergic airway inflammation, these cells are also important for the development of airway hyperreactivity, eosinophilia and Th2 cytokine production in response to antigen challenge. We showed that CD11c+ cells are critical for the recruitment of lung mast cell progenitors and the subsequent increase in mast cells. These CD11c+ cells were needed for the upregulation of endothelial vascular cell adhesion molecule-1 (VCAM-1), which is a prerequisite for the antigen-induced recruitment of lung mast cell progenitors