The role of interleukin-1 and granulocyte-macrophage colony-stimulating factor in the paracrine stimulation of an in vivo-derived murine myeloid leukemia.

WEHI-274.3 is a cell line isolated from an in vivo-derived, murine myelomonocytic leukemia. Although the survival and growth of WEHI-274.3 cells in vitro is absolutely dependent on the addition of exogenous growth factors such as interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or colony-stimulating factor-1, when injected into syngeneic mice the cell line is tumorigenic. Sera from normal mice contain low levels of an activity that sustains survival of WEHI-274.3 but does not stimulate growth. In contrast, sera from mice bearing the WEHI-274.3 leukemia contained levels of CSF-1 and GM-CSF that stimulated the growth of WEHI-274.3 cells. Supernatants of cultures of WEHI-274.3 cells contained an activity that stimulated 3T3 fibroblasts to release an activity that stimulated the growth of the WEHI-274.3 cells. The 3T3-stimulatory activity released by the WEHI-274.3 cells was neutralized completely with an antiserum specific for murine IL-1 alpha, but not with antiserum specific for IL-1 beta. Moreover, WEHI-274.3 cells both in vitro and in vivo contained high levels of IL-1 alpha and IL-1 beta mRNAs. The leukemia-stimulatory activity released by the 3T3 cells was neutralized by an antiserum specific for GM-CSF. We postulate that the IL-1 alpha constitutively released by the WEHI-274.3 cells stimulates the production of GM-CSF from host cells such as fibroblasts or endothelial cells. A similar paracrine mechanism of growth stimulation may occur in acute myeloid leukemias in humans.