Epidermal cells synthesize a cytokine with interleukin 3-like properties.

Interleukin 3 (IL 3) is produced by T lymphocytes and T cell lines (EL 4), as well as by a monomyelocytic cell line (WEHI 3), and it activates lymphocytes as well as mast cells. Recently we have demonstrated that epidermal cells (EC) perform monocyte/macrophage-like functions through the release of an interleukin 1-like immunomodulating mediator (EC-derived thymocyte activating factor; ETAF. Because mast cells predominantly are located in the skin, in the present study we investigated whether EC in addition to ETAF may produce IL 3. Normal as well as transformed keratinocytes were able to secrete an IL 3-like mediator (EC IL 3) that induces the proliferation of IL 3-dependent cell lines. Furthermore, both EC IL 3 and WEHI IL 3 have a similar m.w. of 30,000. In addition, an antibody against IL 3 also blocked EC IL 3 activity, suggesting that these molecules appear to be very similar. EC IL 3 production was greatly enhanced by the addition of concanavalin A, phorbol myristate acetate, lipopolysaccharide, and silica. Factor production was completely blocked by inhibiting protein synthesis. These findings demonstrate that keratinocytes synthesize an additional cytokine with the biologic and biochemical properties of IL 3, but distinct from ETAF. Thus, through the production of EC IL 3, EC may participate in the activation of mast cells and thereby mediate inflammatory as well as hypersensitivity reactions.