Stimulation of DNA synthesis in cultured mouse epidermal cells by human peripheral leukocytes

Primary epidermal cells derived from the skin of newborn mice can be arrested in G1(G0) of the cell cycle when kept in serum-free medium with 0.06 mM Ca++ for 4 days. These cells can be restimulated to grow by the addition of Chelex 100-treated inactivated fetal calf serum, as shown by liquid scintillation counting and autoradiography after [3H]-thymidine incorporation and by counting mitotic figures. This system may be useful in studying growth-promoting and -inhibiting substances in vitro, and it is shown here that leukocytes from peripheral human blood are able to stimulate the DNA synthesis of epidermal cells although the effect is smaller than that observed with serum. The stimulation was not inhibited by pretreatment of leukocytes with mitomycin C, excluding the possibility that the increased incorporation of radioactivity in mixed epidermal-leukocyte cultures is due to increased DNA synthesis in leukocytes stimulated by epidermal cells. Therefore, this system may also be helpful in the investigation of the role of leukocytes in the hyperproliferation of the epidermis.