Thy-1⁺ dendritic epidermal cells belong to the T-cell lineage

The murine epidermis contains a population of dendritic, Thy-1⁺ cells (Thy-1⁺ DEC). Although it is now clear that these cells are of bone marrow origin, extensive morphological, histochemical, and cell-membrane marker studies have not definitively placed them in any known hematopoietic differentiation pathway. Based on the observation that Thy-1⁺ DEC can be propagated in vitro with Con A and interleukin 2, we have established three cell lines (Tehy 184, Tehy 245, and Yety 245) that can be continuously grown in medium with lectin-lymphokine-rich culture supernatants of rat spleen cells. With the exception of the loss of reactivity with anti-asialo-G(M1) antibodies (Tehy 184 and Tehy 245) and the gain of interleukin 2 receptor expression, the cultured cell lines bear the same surface characteristics as freshly isolated Thy-1⁺ DEC: Thy-1⁺, Ly-5⁺, Lyt-1^-, Lyt-2^-, L3T4^-m Ia^-, sIg^-. Using Southern and RNA gel blot analysis, we now demonstrate that these Thy-1⁺ DEC-derived cell lines exhibit various patterns of rearrangements in the gene complexes encoding the T-cell receptor (related) β and γ chains and contain mature and/or incomplete transcripts from the T-cell receptor α- and β-chain genes, as well as transcripts from the receptor-related γ-chain genes. Tehy 184 cells, the only cells containing both mature α- and β-chain transcripts, react positively with the F23.1 monoclonal antibody, which recognizes the product of a subset of T-cell recepor β-chain variable region gene segments. This antibody precipitates a surface protein of 84-88 kDa from these cells that after reduction separates into two 40- to 44-kDa chains, characteristic of Ti α/β heterodimers. These data strongly suggest that Thy-1⁺ DEC belong to the T-cell lineage and point to the epidermis as a site either of immature thymocyte migration or of extrathymic T-cell differentiation.