Long-term cultured adult human keratinocytes secrete granulocyte-macrophage colony-stimulating factor but not interleukin-3 after cytokine exposure in vitro.

To investigate the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF) and of interleukin-3 (IL-3) by human keratinocytes in vitro, adult human keratinocytes (aHKc) from 3 different donors and a spontaneously transformed keratinocytic line (HaCaT) were cultured and exposed to various cytokines and to the protein kinase C-activating agent phorbol-12-myristate-13-acetate (PMA). GM-CSF and IL-3 were measured by highly specific and sensitive immunoassays. Our findings showed that long-term cultured aHKc and HaCaT cells are capable of secreting GM-CSF but not IL-3 upon cytokine and PMA stimulation. Both interleukin-1 and tumor necrosis factor alpha, which are known to be present in human epidermis, particularly during cutaneous inflammatory processes, were found to stimulate GM-CSF release. Therefore, we conclude that increased GM-CSF levels may play an important role in the interactions between epidermal keratinocytes and blood cells in vivo.