A preliminary report: preparations containing Interleukin-3 (IL-3) promote proliferation of multipotential stem cells (CFUs) in the mouse.

The effect of a preparation containing the lymphokine "Interleukin-3" (IL-3) on murine marrow CFUs has been investigated. When marrow cells are incubated for a short period with IL-3 in vitro, the number of spleen colonies that develop upon injection into irradiated recipients is increased. In addition, an increase is seen in the proportion of CFUs killed in vitro by tritiated thymidine. IL-3 does not affect the seeding efficiency of CFUs in the spleen, but appears to act directly on them, not through production of an endogenous marrow stimulator.