[Interleukin 3 (IL-3)].

Interleukin 3 (IL-3) was initially described in the supernates of cultures of viral-infected murine spleen cells, as a cytokine produced by T lymphocytes can promote differentiation of immature T lymphocytes. Later, it was found that IL-3 exhibited a striking effect on hematopoiesis. The recombinant molecule of murine and human IL-3 can promote the sustained proliferation of clones of mast cells and basophils. It also acts as a colony stimulating factor (CSF) for bone marrow cells. Although other CSFs generally stimulate specific lineages of myeloid or erythroid cells, IL-3 stimulates bone marrow to induce proliferation of a variety of clonal cell populations, including colonies of granulocytes, macrophages, megakaryocytes, eosinophils, basophils, mast cells, normoblasts and erythroblasts. Thus, IL-3 is responsible for promoting proliferation of earlier lineage pluripotent stem cells, of hematopoietic cells and lymphoid cells. Recently, it is also suggested, as to its effects on lymphocytes, that IL-3 may possibly be a factor responsible for T lymphocytes to be differentiating extra-thymically.