RESUMO
BACKGROUND: Lung-homing of progenitor cells is associated with inflammatory and remodelling changes in asthma. Factors that modulate the increased traffic of progenitor cells to the site of inflammation in asthma remain to be defined. Interleukin (IL)-4 and IL-13 are Th2 cytokines that are key regulators of asthma pathology. OBJECTIVE: We investigated the role of IL-4 and IL-13 in modulating the trans-migrational responses of haemopoietic progenitor cells (HPC). METHODS: HPC were enriched from cord blood (CB) and peripheral blood (PB) samples. Migration of HPC was assessed using transwell migration assays, and responding cells were enumerated by flow cytometry. RESULTS: IL-4 and IL-13 primed migration of CB- and PB-derived HPC (CD34(+) 45(+) cells) to stromal cell-derived factor-1α (SDF-1α), in vitro. However, these cytokines had no effect on migrational responses of eosinophil-lineage committed progenitors (CD34(+) 45(+) IL-5Rα(+) cells) or mature eosinophils to SDF-1α. For HPC, priming effects of IL-4 (0.1 ng/mL) and IL-13 (0.1 ng/mL) were detectable within 1 h and optimal at 18-h post-incubation, and IL-4 was the more effective priming agent. Pre-incubation with IL-4 or IL-13 had no effect on the intensity of cell surface expression of SDF-1α receptor, CXCR4. Disruption of cell membrane cholesterol content by pre-incubation with polyene antibiotics inhibited IL-4 priming of SDF-1α stimulated migration of HPC indicating that increased incorporation of CXCR4 into membrane lipid rafts mediated the cytokine primed migrational response of HPC. This was confirmed by confocal fluorescent microscopy. CONCLUSIONS AND CLINICAL RELEVANCE: IL-4 and IL-13 prime the migrational response of HPC to SDF-1α by enhancing the incorporation of CXCR4 into lipid rafts. The priming effect of these cytokines is specific to primitive HPC. These data suggest that increased local production of IL-4 and IL-13 within the lungs may promote increased SDF-1α mediated homing of HPC to the airways in asthma.