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Description

Interleukin-5 (UniProt: P05113, also known as IL-5, B-cell differentiation factor I, Eosinophil differentiation factor, T-cell replacing factor, TRF) is encoded by the IL5 gene (Gene ID: 3567) in human. IL-5 is a disulfide-linked homodimeric secreted protein that is synthesized and secreted mainly by the activated CD4+ helper T cells of the Th2 subset, mast cells, and eosinophils. It is synthesized with a signal peptide (aa 1-19), which is subsequently cleaved off to produce the mature protein (aa 20-134). It serves as a powerful proinflammatory cytokine that is responsible for maturation, proliferation, activation, and migration of eosinophils. It is also a key factor in the upregulation of myeloid progenitors in the bone marrow after airway allergen challenge, and for trafficking from the marrow to the airways in upper or lower airways inflammation. Its biological effects are mediated via selective interaction with IL-5 receptor (IL-5R), which is composed of an a subunit (IL-5Ra) and a non-specific betac heterodimer. As a homodimer it binds to IL-5Ra expressed on eosinophil surface and recruits the betac dimer and induces the assembly of the IL-5/IL-5Ra/betac ternary complex. In the absence of IL-5, IL-5Ra is complexed with the intracellular JAK2, whereas the betac subunit is associated with JAK1. (Ref.: Pelaia, C., et al. (2019). Front. Physiol. 10, 1514).