Abstract
Pulmonary eosinophilia, a hallmark pathologic feature of allergic lung disease, is regulated by interleukin-13 (IL-13) as well as the eotaxin chemokines, but the specific role of these cytokines and their cooperative interaction are only partially understood. First, we elucidated the essential role of IL-13 in the induction of the eotaxins by comparing IL-13 gene-targeted mice with wild type control mice by using an ovalbumin-induced model of allergic airway inflammation. Notably, ovalbumin-induced expressions of eotaxin-1 and eotaxin-2 mRNA in the lungs were almost completely dependent upon IL-13. Second, in order to address the specific role of eotaxin-2 in IL-13-induced pulmonary eosinophilia, we generated eotaxin-2 gene-deficient mice by homologous recombination. Notably, in contrast to observations made in eotaxin-1-deficient mice, eotaxin-2-deficient mice had normal base-line eosinophil levels in the hematopoietic tissues and gastrointestinal tract. However, following intratracheal IL-13 administration, eotaxin-2-deficient mice showed a profound reduction in airway eosinophilia compared with wild type mice. Most interestingly, the level of peribronchial lung tissue eosinophils in IL-13-treated eotaxin-2-deficient mice was indistinguishable from wild type mice. Furthermore, IL-13 lung transgenic mice genetically engineered to be deficient in eotaxin-2 had a marked reduction of luminal eosinophils. Mechanistic analysis identified IL13-induced eotaxin-2 expression by macrophages in a distinct lung compartment (luminal inflammatory cells) compared with eotaxin-1, which was expressed solely in the tissue. Taken together, these results demonstrate a cooperative mechanism between IL-13 and eotaxin-2. In particular, IL-13 mediates allergen-induced eotaxin-2 expression, and eotaxin-2 mediates IL-13-induced airway eosinophilia.
Highlights
Pulmonary eosinophilia, a hallmark pathologic feature of allergic lung disease, is regulated by interleukin-13 (IL-13) as well as the eotaxin chemokines, but the specific role of these cytokines and their cooperative interaction are only partially understood
IL-13 Is Required for Eotaxin-1 and Eotaxin-2 Induction—We were first interested in determining the specific molecules associated with allergen-induced Th2 responses that were responsible for mediating induction of the eotaxins
Recent attention concerning the pathogenesis of allergic lung disease has focused on understanding the role of IL-13 because it has been identified as an important regulator of multiple aspects of experimental disease including AHR, eosinophilia, FIG. 7
Summary
A hallmark pathologic feature of allergic lung disease, is regulated by interleukin-13 (IL-13) as well as the eotaxin chemokines, but the specific role of these cytokines and their cooperative interaction are only partially understood. By using experimental models of antigen-induced airway inflammation, eotaxin-1 has been demonstrated to partially regulate eosinophil recruitment during the late phase response following repetitive mucosal antigen challenges [37, 38] Mice deficient in both eotaxin-1 and IL-5 have a synergistic deficiency of lung eosinophils compared with mice deficient in either cytokine alone [39]. Mechanistic analysis identified IL-13-induced eotaxin-2 expression in a distinct cellular compartment (airway lumen) compared with eotaxin-1, which was solely expressed by cells found in the lung tissue Taken together, these results identify a linear relationship in which allergen induces IL-13, which in turn is required for eotaxin-2 induction, which in turn regulates airway eosinophilia in a manner distinct from eotaxin-1
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