Interleukin-4 and interleukin-13 prime migrational responses of haemopoietic progenitor cells to stromal cell-derived factor-1α.

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.

Human airway smooth muscle promotes eosinophil differentiation.

INTRODUCTION: Human airway smooth muscle (HASM) cells in culture synthesize cytokines and chemokines that may orchestrate the tissue homing and in situ differentiation of haemopoietic progenitor cells from the peripheral circulation. OBJECTIVE: To study the effect of a supernatant from cultured HASM cells on the differentiative and transmigrational responses of haemopoietic progenitor cells. METHODS: HASM cells were grown to confluence and stimulated with a cytomix of TNF-alpha, IL-1beta and IFN-gamma. Peripheral blood-derived progenitors from atopic asthmatics (n=12) and non-atopic controls (n=11) were grown in a methylcellulose culture with a supernatant from stimulated HASM cells to assess clonogenic potential. The ability of HASM cells to stimulate directional migration and adhesion to fibronectin of blood progenitors was also investigated. RESULTS: HASM cells stimulated significant growth of eosinophil/basophil colony forming units (Eo/B CFUs) from blood progenitor cells from both groups of subjects. This activity was significantly attenuated in the presence of anti-IL-5 and anti-granulocyte macrophage-colony forming factor blocking antibodies and by pre-treatment with SB202190 [p38 mitogen-activated protein kinase (MAPK) inhibitor]. An src kinase (srcK) inhibitor (Pyrazolopyrimidine 1) was less effective at attenuating IL-5- and HASM-stimulated Eo/B CFU growth from both groups of subjects. Examination of the phosphorylation of these kinases in CD34(+) cells following co-incubation with the major constituents of HASM showed activation of p38 MAPK but not that of the srcK pathway. The HASM supernatant had no significant effect on the migrational and adhesive responses of haemopoietic progenitor cells in vitro. CONCLUSION: We have shown that HASM cell-derived cytokines promote eosinophil differentiation that is dependent on p38 MAPK but not on the srcK pathway. This study shows that a major structural cell of the lungs, airway smooth muscle, has the capability to direct eosinophil differentiation and maturation from progenitor cells, which in turn may perpetuate an eosinophilic inflammation and consequently tissue remodelling in patients with chronic asthma.