Interleukin 5 (IL5) is an interleukin produced by type-2 T helper cells and mast cells.Through binding to the interleukin-5 receptor, interleukin 5 stimulates B cell growth and increases immunoglobulin secretion - primarily IgA. It is also a key mediator in eosinophil activation.IL-5 is a 115-amino acid (in human, 133 in the mouse) -long TH2 cytokine that is part of the hematopoietic family. Unlike other members of this cytokine family (namely interleukin 3 and GM-CSF), this glycoprotein in its active form is a homodimer.