Interleukin‐9 stimulates in vitro growth of mouse thymic lymphomas

The ability of interleukin (IL)-9 to stimulate the in vitro proliferation of freshly collected mouse thymic lymphoma cells was tested on a panel of 45 tumors, induced by N-methyl-N-nitrosourea (MNU) or by X-ray irradiation. IL-9 significantly stimulated the proliferation of 26 of these tumors. Out of 11 other factors tested, only IL-2, IL-4 and IL-7 showed similar activities. In addition to the responses to IL-9 alone, a potent synergy was often observed between IL-9 and IL-2 for MNU-induced tumors. Synergies between IL-9 and IL-7 or IL-9 and IL-4 were also observed but less frequently. The growth-promoting activity of IL-9 and the synergistic activities of IL-2 and IL-9 for thymic lymphoma cells were confirmed with cell lines established from the fresh tumors.