Interleukin 5 is a T cell-derived factor that promotes the proliferation, differentiation and activation of eosinophils. In mice, IL-5 has also been shown to be a growth and differentiation factor for B cells. Various names previously used to describe IL-5 include: T cell replacing factor (TRF), B cell growth factor II (BCGFII), B cell differentiation factor μ (BCDF μ), eosinophil differentiation factor (EDF) and eosinophil colony-stimulating factor (Eo-CSF). Biologically active IL-5 is a disulfide-linked homodimer. The cDNAs for murine and human IL-5 encode precursor proteins with signal peptides that are cleaved to form mature proteins containing 113 and 115 amino acid residues, respectively. Murine and human IL-5 are 70% identical in their amino acid sequences and show species cross‑reactivity. The genes for human and mouse IL-5 have been mapped to chromosome 5 and chromosome 11, respectively; closely linked to the genes for IL-3, IL-4 and GM-CSF.
IL-5 exerts its activity on target cells by binding to specific cell surface receptors. The functional high‑affinity receptor for human IL-5 has been shown to be composed of a low-affinity IL-5 binding alpha -subunit and a non-binding common beta -subunit that is shared with the high‑affinity receptors for GM‑CSF and IL-3.
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