INTERLEUKINS | IL-5

Interleukin-5 (IL-5) is a cytokine secreted principally by activated helper T cells of the T-helper-2 (Th2) subset. IL-5 is a short chain helical bundle cytokine structurally similar to IL-3, IL-4, and granulocyte-macrophage colony-stimulating factor. The IL-5 gene is tightly linked with the IL-4 and IL-13 genes in a Th2 cytokine gene cluster on chromosome 5q, and the expression of these genes is coordinately regulated. The biology of IL-5 has been best studied in the context of asthma in humans and allergic airway inflammation in mouse models. IL-5 directly mediates eosinophilic inflammation by stimulating the differentiation, proliferation, recruitment, survival, and activity of eosinophils. Eosinophils release granule proteins and leukotrienes that are hypothesized to contribute to airway hyperreactivity and epithelial damage in allergic asthma. However, recent studies indicate that the immunopathogenic role of IL-5 and eosinophils in asthma is not clear.