Interleukin-5: an eosinophil growth and activation factor.

A mouse lymphokine stimulating eosinophil differentiation has been identified and characterized. This factor was found to be identical to B cell growth factor II, and is now called interleukin-5 (IL5). Although this murine factor stimulated human eosinophil differentiation and activation, it had no detectable activity on human B cells. Following the cloning of the mouse factor, the human gene was cloned and expressed. Like the mouse factor human IL5 stimulates the production and activation of human eosinophils. However, unlike mouse IL5 which has a readily detectable activity on murine B cells, the human factor was negative when tested in a variety of assays on human B cells.