Role of IL-5 in Immune and Pathological Responses in the Mouse

Studies in interleukin (IL)-5-/- mice have shown that this cytokine plays a critical role in the regulation of eosinophil expansion in the bone marrow and blood in response to allergic and parasitic stimuli. IL-5 also plays a central role in regulating baseline blood and tissue eosinophil numbers but is not essential for eosinophil development or migration. Thus, eosinophil accumulation into allergic tissues should not be viewed as a process that is exclusively regulated by IL-5, but one that is greatly enhanced by this cytokine. Although IL-5 regulated eosinophilia plays an important role in the regulation of allergic inflammation and the subsequent development of disease, its role in the elimination of parasites and in nonallergic disease processes is less clear. This may stem from the observation that eosinophils can accumulate in tissues independently of IL-5 and that these alternative pathways coexist in many disease and immune responses. Importantly, studies in IL-5-/- mice are disclosing an important role for this cytokine in the regulation of immune responses by modulating lymphocyte function.