The protein encoded by this gene is a cytokine that acts as a growth and differentiation factor for both B cells and eosinophils. This 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 this cytokine is a heterodimer，whose beta subunit is shared with the receptors for interleukine 3 （IL3） and colony stimulating factor 2 （CSF2/GM-CSF）. This gene，together with those for interleukin 4 （IL4），interleukin 13 （IL13），and CSF2，form a cytokine gene cluster on chromosome 5. This cytokine，IL4，and IL13 are found to be regulated coordinately by long-range regulatory elements spread over 120 kilobases on chromosome 5q31.
