Modulation of β1-integrins on hemopoietic progenitor cells after allergen challenge in asthmatic subjects

Background: Mobilization of hemopoietic progenitor cells from the bone marrow (BM) is a feature of inflammatory asthmatic responses. Understanding the mechanisms regulating progenitor cell mobilization and trafficking to the peripheral circulation might be important for the development of effective asthma therapies. Objective: We investigated the role of adhesion molecules in the mobilization of hemopoietic progenitor cells from the BM during an allergen-induced asthmatic response. Methods: BM and peripheral blood samples were obtained from dual-responders with mild asthma before and at several time points after allergen challenge. Fluctuations in expression and adhesive properties of beta 1- and beta 2-integrins on CD34(+)CD45(+) progenitor cells were assessed by using flow cytometry and adhesion to protein-coated wells, respectively. Results: On BM-derived CD34(+)CD45(+) cells, expression of very late antigen (VLA) 4, but not VLA-5 or Mac-1, decreased significantly 24 hours after allergen challenge and had begun to recover by 48 hours after challenge. In peripheral blood allergen challenge induced a significant decrease in VLA-4 levels after 6 hours, which had not recovered by 96 hours after challenge. Similarly, VLA-5 expression decreased, most prominently at 72 to 96 hours after allergen challenge. In contrast, Mac-1 levels did not change. Chemokine-stimulated adhesion of BM-derived CD34+CD45+ cells to fibronectin was significantly attenuated 24 hours after challenge. Furthermore, adhesion to fibronectin and vascular cell adhesion molecule I was greatly reduced by anti-VLA-4 or anti-VLA-5 antibodies. Conclusions: Preferential downregulation of beta 1-integrin expression on progenitor cells can reduce the tethering forces to BM components, thus facilitating their egress to the peripheral circulation during an allergic inflammatory response.