In the current study we used a well-characterized mouse model of allergen-induced airway inflammation to determine the role of CCR3 receptor–ligand interactions in the migration and function of CD34+ cells. Allergen exposure significantly increased BM, blood and airway CD34+ CCR3+ cells as well as airway CD34+ CCR3+ stem cell antigen-1-positive (Sca-1+) and CD34+ CD45+ interleukin-5 receptor-α-positive (IL-5Rα+) cells. A portion of the newly produced CD34+ CCR3+, Sca-1+ CCR3+ and IL-5Ralpha+ lung cells showed a significant proliferative capacity in response to allergen when compared with saline-treated animals. In addition, in vitro colony formation of lung CD34+ cells
was increased by IL-5 or eotaxin-2 whereas eotaxin-2 had no effect on BM CD34+ cells. Furthermore, both eotaxin-1 and eotaxin-2 induced migration of BM and blood
CD34+ CCR3+ cells in vitro. These data suggest that the CCR3/eotaxin click here pathway is involved in the regulation of allergen-driven in situ haematopoiesis and the accumulation/mobilization of eosinophil-lineage-committed progenitor cells in the lung. Hence, targeting both IL-5 and CCR3-mediated signalling pathways may be required to control the inflammation associated with allergen-induced asthma. Allergic airway inflammation LY2835219 in vitro in asthma is dominated by eosinophils, which develop from CD34+ haematopoietic progenitor cells within the bone marrow (BM).1–7 Evidence increasingly suggests that in addition to the trafficking of mature eosinophils from the BM to the airways, migration of immature cells and progenitors from the BM to sites of inflammation can also occur during an allergic inflammatory response.8–11 Increased numbers of CD34+ cells in BM and airways has been reported in atopic individuals and in individuals with ongoing asthma or allergic rhinitis.12,13 To date, however, it is not clear which chemotactic factors induce the very traffic of these cells to the airways during an allergic inflammatory
response. It is known that the eotaxin receptor, CC chemokine receptor 3 (CCR3) is expressed on human CD34+ BM cells and that asthmatics with late responses to allergen have increased numbers of BM CD34+ CCR3+cells 24 hr after allergen challenge.14,15 These findings imply that variations in CCR3 expression on BM CD34+ cells may facilitate chemokine-mediated progenitor cell mobilization to the peripheral circulation and that eotaxins may orchestrate the homing of CD34+ cells to tissue sites of allergic inflammation. Furthermore, results from clinical studies using humanized monoclonal anti-interleukin-5 (IL-5) clearly demonstrate that eosinophils are able to reside in the tissue despite blockade of IL-5.16 These findings highlight unidentified signals that promote eosinophil survival and proliferation in vivo in response to allergen challenge and that need further investigation.