The role of interleukin-3 in the proliferation of murine mast cells in vitro

We studied the role of interleukin-3 (IL-3) in the growth of murine mast cells in the methylcellulose culture system. A mature mast cell population was prepared from the liquid culture of pooled mast cell colonies. In the presence of IL-3, primary mast cell colonies were formed from total spleen cells, but secondary mast cell colonies were not formed from the homogeneous population of mast cells. Pokeweed mitogen-spleen cell-conditioned medium (PWM-SCM) supported the secondary mast cell colony formation. To clarify the supportive role of IL-3 in mast cell growth, we carried out the delayed addition of PWM-SCM to the dishes with or without IL-3. When PWM-SCM was added to the mast cells supported by IL-3 for 9 days, the number of colonies was significantly increased, while no colony-forming cells survived in the absence of hemopoietic factors. These experiments suggest that IL-3 supports the differentiation of mast cells in the presence of accessory cells, but does not expand the mast cell population, and that other factor(s) are required.