Interleukin-3 (IL3) is a pleiotropic cytokine primarily produced by activated T-lymphocytes as well as mast cells and osteoblastic cells. It can stimulate the proliferation and differentiation of hematopoietic stem cells and various lineage-comitted progenitors. IL3 affects the functional activity of mature mast cells, basophils, eosinophils and monocytes. It also plays a crucial role in neural cell proliferation and survival. Moreover, IL3 participates in bone homeostasis, and inhibits osteoclast differentiation by preventing NF-kappa-B nuclear translocation and activation. Mechanistically, IL3 exerts its biological effects through a receptor composed of IL3RA subunit and the signal transducing subunit IL3RB. Upon receptor stimulation, JAK2 kinase is rapidly activated, leading to STAT5-mediated transcriptional program. Alternatively, under oxidative stress in non-hematopoietic systems, IL3 contributes to cell survival by activating pathways mediated by PI3K/AKT and ERK.