Human IL-5 Recombinant Protein. IL-5 is a cytokine that acts as a growth and differentiation factor for both B cells and eosinophils. IL-5 cytokine is a main regulator of eosinopoiesis, eosinophil maturation and activation. The elevated production of this cytokine is reported to be related to asthma or hypereosinophilic syndromes. The receptor of IL-5 cytokine is a heterodimer, whose beta subunit is shared with the receptors for interleukine 3 (IL3) and colony stimulating factor 2 (CSF2/GM-CSF). IL-5, together with those for interleukin 4 (IL4), interleukin 13 (IL13), and CSF2, form a cytokine gene cluster on chromosome 5. IL-5, IL4, and IL13 are found to be regulated coordinately by long-range regulatory elements spread over 120 kilobases