Interleukin 3 (IL3) is a cytokine that regulates hematopoiesis by controlling the production, differentiation and function of granulocytes and macrophages.
The protein, which exists in vivo as a monomer, is produced in activated T cells and mast cells, and is activated by the cleavage of an N-terminal signal sequence.
IL3 is produced by T lymphocytes and T-cell lymphomas only after stimulation with antigens, mitogens, or chemical activators such as phorbol esters.
However, IL3 is constitutively expressed in the myelomonocytic leukemia cell line.
It is thought that the genetic change of the cell line to constitutive production of IL3 is the key event in development of this leukaemia.