Interleukin-5 (IL-5) is a hematopoietic growth factor expressed in Th2, mast cells and eosinophils. IL-5 acts through its receptor, the IL-5 receptor (IL-5R) and is involved in B cell growth and eosinophil activation. IL-5 has been shown to be and is regulated by GATA-3, in addition to other transcription factors. and IL-5 are cross-reactive. Recombinant IL-5 is a non-glycosylated, disulfide-linked homodimer, containing two 113 amino acid chains, with a total molecular weight of 26.2 kDa.