In Vitro Induction of Proliferation and Differentiation of Uncommitted Spleen Cells by Epidermal Cell-Derived Cytokines

In this study of the hematopoietic functions of the cytokines released by the epidermal cells, we examined the effects of culture supernatants of epidermal cells and dermal cells from new born mice on uncommitted spleen cells. The epidermal cell culture supernatants (ECCS) stimulated the proliferation of nylon wool-passed I-A-spleen mononuclear cells (SC) much more vigorously than did the dermal cell culture supernatants (DCCS). The main responding cells were I-A^-Thy-l^-Lyt-l^-Lyt>2^- cells. Giemsa staining of cytocentrifuge preparations disclosed that SC cultured with ECCS or DCCS were composed of about 50% lymphoid cells, 30-40% granulocytes, 10% macrophages, and a few mast cells and megakaryocytes. Immunoperoxidase staining of the cytocentrifuge preparations showed that SC cultured with ECCS consisted of less than 10% I-A^-, about 40% Thy-1⁺, 10-20% Lyt-1⁺, less than 6% Lyt-2⁺, 30-40% Mac-1⁺, 10-30% Mac-2⁺, 40-55% Mac-3⁺, and 10-20% Asialo-GMl⁺ cells. A double immunofluorescence study showed that 11% of Mac-1⁺ cells, 34% of Mac-2⁺ cells and 14% of Mac-3⁺ cells were I-A⁺, whereas all the I-A⁺ cells were either Mac-1⁺, Mac-2⁺, or Mac-3⁺, and that the percentage of Thy-l⁺Asialo-GMl⁺ was less than 5%. In a panel of 3 available purified cytokines known to be secreted by keratinocytes which were used as a positive control, a similar stimulatory effect was recognized with GM-CSF and IL-3 but no such effect was found with recombinant IL-1. These data suggest that ECCS can stimulate the development of uncommitted SC into lymphocytes, different subsets of macrophages probably including Langerhans cells, granulocytes, mast cells and megakaryocytes. They constitute direct and convincing evidence indicating the combined effect of various cytokines released by epidermal cells on the proliferation and maturation of hematopoietic precursor cells into different immunocompetent cells in the skin.