We describe a bioassay that allows the in vitro investigation of the stimulatory and suppressive factors derived from immune cells in short-term cultures of human keratinocytes. In agreement with other assays, epidermal growth factor is not mitogenic for human keratinocytes. Supernatant fluid from human PBMC stimulated with Con A, from allo-MLRs, as well as supernatants from nonstimulated PBMC, possess growth-promoting molecules. Our results show that both activated and nonactivated T cells release growth factors. Suppressive molecules are produced preferentially by monocyte cultures. Two T cell products, IFN-gamma and transforming growth factor beta are both inhibitory for keratinocyte proliferation. Two other T cell products, IL-3 and GM-CSF, stimulate keratinocyte proliferation at nanogram concentrations. These results suggest the existence of regulatory circuits between the T cells of a dermal inflammatory infiltrate and the overlying epidermal keratinocytes. This may determine the fine control of epidermal proliferation and turnover leading either to enhanced wound repair or skin pathology.

This content is only available as a PDF.