Allergic airway inflammation and bone marrow eosinophilopoiesis. Modulation by cytokines

Abstract

Accumulation of eosinophils in the airways and lung parenchyma is one of the hallmarks of allergic airway inflammation. This cellular inflammatory response is likely to involve the release of eosinophils from peripheral storage pools and possibly cause production of eosinophils in the bone marrow (BM). In exacerbations of asthma, prolonged airway eosinophilia is commonly observed. Cytokines play a critical role in the orchestration of allergic airway inflammation. IL-5 is the major cytokine regulating eosinophilia in allergic disease. IL-5 not only increases the number of eosinophils but also enhances their function. Several cytokines, for example IL-12, Interferon gamma (IFN- ) and IL-10, have anti-inflammatory effects in allergic inflammation. IL-12 is the endogenous regulator of Th1 cell development and determines the balance between Th1 and Th2 cells. IL-12 directs naive T cells to develop into Th1 cells and enhances the production of IFN- IFN- has an inhibitory effect on Th2 cells, thus reducing the synthesis of IL-4, IL-5 and has been shown to reduce eosinophilic cell infiltration into the airways. There are different possible ways to inhibit the effects of IL-5, such as by antagonists of the IL-5 receptor expressed on the surface of eosinophils, monoclonal antibodies to IL-5 and soluble IL-5 receptors. The aim of this thesis was to determine whether airway allergen exposure increases bone marrow eosinophil production, and thus whether eosinophilopoiesis is enhanced. This would elucidate the contribution of newly produced eosinophils in the prolonged airways allergic inflammation and the cytokines' modulating role in these processes. After OVA sensitization and exposure, cells from BAL, blood and BM were analyzed. To identify IL-5 producing cells in the bone marrow, we used a flow cytometer. BM cells were cultured to evaluate IL-5 protein release. IL-5 receptor positive cells were detected by immunocytochemistry staining. We used the thymidine analogue bromodeoxyuridine (BrdU) to identify the newly produced cells. To evaluate the role of IL-5 in the airways inflammation, we give anti IL-5 systemically. To evaluate any modulating role of IL-12 and IFN- we used IL-12 and IFN- receptor knockout mice and matched wild type mice. Repeated airway allergen exposure induces airway eosinophilia, bone marrow eosinophilopoiesis and enhanced bone marrow responsiveness in vitro. Both CD3+ and non-CD3 cells acquired from the bone marrow expressed and released IL-5-protein. Anti-IL-5 given systemically inhibited both airway and bone marrow eosinophilia. Bone marrow cells, but not BAL eosinophils, displayed stainable amounts of the IL-5R -chain. IL 12 KO mice showed higher eosinophil levels in both BAL and bone marrow than wild type mice. BAL eotaxin levels were increased in IL 12 KO. Three weeks after allergen exposure, only IFN- R KO mice kept increased eosinophil levels in BAL, blood and BM. Approximately 50% of BAL granulocytes were BrdU-positive in IFN- R KO mice. In conclusion, bone marrow is activated after allergen exposure, and IL-5 plays a crucial role in this process. T lymphocytes are one of several sources of IL-5 in bone marrow. Anti IL-5 given systemically is effective in reducing both airway and BM eosinophilia. Newly produced eosinophils contribute to prolonged airways inflammation. Cytokines IL-12 and IFN- have modulatory effects in allergic airways inflammation, partly via effects in the bone marrow.