Human keratinocytes and epidermoid carcinoma cell lines produce a cytokine with interleukin 3-like activity.

Keratinocytes are capable of releasing distinct immunomodulating cytokines such as epidermal cell-derived thymocyte activating factor (ETAF) and an epidermal cell-derived natural killer cell augmenting factor (ENKAF). The present study was performed to determine whether human keratinocytes also may secrete an interleukin 3 (IL-3)-like mediator and thereby participate in the regulation of mast cell activity in the skin. Supernatants of freshly isolated human epidermal cells (EC) and malignant keratinocyte cell lines (A 431, SCC) were tested for their capacity to induce the proliferation of IL-3-dependent cell lines 32 DCL and FDCP. Human epidermal cell interleukin 3 (EC IL-3) is spontaneously released by freshly isolated EC, A 431, and squamous cell carcinoma (SCC) cells. However, both normal EC and A 431 cells produced increased levels of EC IL-3 activity when cultured in the presence of different stimulants, such as phorbol myristate acetate and lipopolysaccharide. The EC IL-3 activity was not inhibited when treated with a monoclonal anti-IL-1 or anti-IL-2-antibody. Biochemical characterization showed that human EC IL-3 has a molecular weight of 17K, elutes of DEAE-ion exchange high-performance liquid chromatography (HPLC) as one major peak at 0.36 M NaCl, and upon HPLC-chromatofocusing exhibits 3 isoelectric points of 7.8, 7.5, and 5.6. Upon reversed-phase HPLC, EC IL-3 activity eluted at about 100% acetonitrile. When highly purified EC IL-3 was labeled with 125I and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a single homogeneous band exhibiting a molecular weight of 17K was seen, which correlated with the IL-3 activity and was free of ETAF/IL-1, IL-2, and interferon activity. These data indicate that human EC synthesize an IL-3-like cytokine which is distinct from ETAF/IL-1, IL-2, and interferon and thereby may participate in the regulation of mast cell activity during inflammatory and fibrotic, as well as hypersensitivity reactions.