Distinct mechanisms may account for the growth-promoting activity of interleukin 3 on cells of lymphoid and myeloid origin.

We have investigated whether interleukin 3 (IL-3) supports the growth of cells of different lineages by the same mechanism(s). The experiments were carried out with Ea3 cells, a mouse pre-B cell line, and S-480-3 cells, a mouse basophil cell line, both of which are totally IL-3 dependent. We found that Ea3 lymphocytes but not S-480-3 basophils absorb partially purified IL-3. Both Ea3 and S-480-3 cells respond to IL-3 by increasing anaerobic glycolysis as determined by lactic acid production. S-480-3 cells responded to exogenous ATP by maintaining proliferation and reducing lactic acid production, but Ea3 lymphocytes are refractory to exogenous ATP. We conclude that there may be two distinct mechanisms by which cells respond to IL-3, indicated by early events concerning the binding of IL-3 and the effect of exogenous ATP on respiratory metabolism. One appears to be a ligand-receptor-mediated mechanism in lymphoid cells and the other to be a mechanism that is partially replaceable by exogenous ATP in nonlymphoid cells not associated with lymphoid-like receptors. Our findings may explain (i) the apparent variety of cell lineages promoted by IL-3 by a widely available mechanism that supports glycolysis and, therefore, enables both proliferation and possibly expression of binding sites for lineage specific differentiation factors and (ii) the existence of lymphocytes that express receptors specific for IL-3 and are inducible for other characteristics and functions in a regulated manner.