Description_x000D_ Biochem/physiol Actions_x000D_ Interleukin-3 (IL-3) is a multifunctional protein, originally called colony forming unit-stimulating activity (CFU-SA), and is produced by activated T lymphocytes. IL-3 supports the formation of multilineage colonies in the early development of multipotent hematopoietic progenitor cells. IL-3 has been shown to induce colony formation of macrophages, neutrophils, mast cells, and megakaryocytes from agar-suspended bone marrow cells. IL-3 also interacts with IL-2 to stimulate growth of T lymphocytes and to induce IgG secretion from activated B cells. Other synonyms for IL-3 include pan-specific hemopoietin, multicolony stimulating factor, mast cell growth factor, burst promoting activity, histamine-producing cell stimulating factor, P cell stimulating factor, and WEHI-3 factor._x000D_ Physical form_x000D_ Lyophilized with no additives. Sterile filtered through a 0.2 μm filter._x000D_ Analysis Note_x000D_ The biological activity is measured by the dose-dependent stimulation of the proliferation of human TF-1 cells.