Pathogenesis of Murine Experimental Allergic Rhinitis: A Study of Local and Systemic Consequences of IL-5 Deficiency

Abstract

Recent studies have demonstrated an important role for IL-5-dependent bone marrow eosinophil progenitors in allergic inflammation. However, studies using anti-IL-5 mAbs in human asthmatics have failed to suppress lower airway hyperresponsiveness despite suppression of eosinophilia; therefore, it is critical to examine the role of IL-5 and bone marrow responses in the pathogenesis of allergic airway disease. To do this, we studied the effects of IL-5 deficiency (IL-5-/-) on bone marrow function as well as clinical and local events, using an established experimental murine model of allergic rhinitis. Age-matched IL-5+/+ and IL-5-/- BALB/c mice were sensitized to OVA followed by 2 wk of daily OVA intranasal challenge. IL-5-/- OVA-sensitized mice had significantly higher nasal mucosal CD4+ cells and basophilic cell counts as well as nasal symptoms and histamine hyperresponsiveness than the nonsensitized group; however, there was no eosinophilia in either nasal mucosa or bone marrow; significantly lower numbers of eosinophil/basophil CFU and maturing CFU eosinophils in the presence of recombinant mouse IL-5 in vitro; and significantly lower expression of IL-5Rα on bone marrow CD34+CD45+ progenitor cells in IL-5-/- mice. These findings suggest that IL-5 is required for normal bone marrow eosinophilopoiesis, in response to specific Ag sensitization, during the development of experimental allergic rhinitis. However, the results also suggest that suppression of the IL-5-eosinophil pathway in this model of allergic rhinitis may not completely suppress clinical symptoms or nasal histamine hyperresponsiveness, because of the existence of other cytokine-progenitor pathways that may induce and maintain the presence of other inflammatory cell populations. Show more