Thy-1⁺ epidermal cells proliferate in response to Concanavalin A and interleukin 2

Mouse epidermal cells (EC) are composed of at least two phenotypically discrete populations of cells that in epidermal sheets have a dendritic morphology: Ia⁺ Langerhans cells (LC) and dendritic, bone marrow-derived, Ia^- cells that express Thy-1 antigen (Thy-1⁺ dEC). Thy-1⁺ dEC lack other typical T cell markers such as L3T4, Lyt-1, and Lyt-2; however, they do express Ly-5 and asialo GM₁ in common with NK cells and certain other leukocytes. To investigate the functional capabilities of Thy-1⁺ dEC in vitro, cell suspensions prepared from trypsin-disaggregated sheets of mouse body wall epidermis were first enriched to 8 to 20% Ia⁺ and 20 to 40% Thy-1⁺ cells by centrifugation over Isolymph and then were cultured for 2 to 10 days with Concanavalin A (Con A) and/or partially purified rat IL 2. Con A-induced proliferation of EC was readily seen, with the maximal response occurring at a Con A concentration of 2.5 μg/ml on day 5 of culture. Con A responses were significantly enhanced by the continuous presence of 1 μg/ml indomethacin. Responses both in the presence and absence of Con A were significantly enhanced by the addition of 5 to 10 U/ml of partially purified rat IL 2; proliferation in cultures stimulated by both Con A and IL 2 continued to increase throughout the 10-day culture period. Culture of fluorescence-activated cell sorter (FACS)-separated EC suspensions revealed that Thy-1-depleted EC and irradiated Thy-1⁺ EC failed to proliferate in response to Con A and IL 2, whereas unirradiated purified Thy-1⁺ EC gave enhanced Con A- and IL 2-induced responses compared with the unseparated population. Finally, to distinguish between the proliferation of small numbers of mature peripheral T cells and that of Thy-1⁺ dEC, antibody and complement-depletion studies were conducted with an unusual monoclonal anti-Thy-1 reagent, 20-10-5S, and with the anti-T cell reagents, anti-L3T4 and anti-Lyt-2. Thy-1⁺ dEC, but not LC, express the 20-10-5S determinant; furthermore, in CBA (Thy-1.2) mice 20-10-5S reacts with Thy-1⁺ dEC, thymocytes, and peripheral T cells, whereas in AKR/J (Thy-1.1) mice, it reacts only with Thy-1⁺ dEC and thymocytes and not with peripheral T cells. Pretreatment of AKR/J EC with 20-10-5S and complement abolished the capacity of such cells to respond to Con A and to IL 2. Furthermore, pretreatment of CBA EC with anti-L3T4, anti-Lyt-2.1, and complement failed to diminish the proliferative response of these cells. These results suggest strongly that Thy-1⁺ dEC, which do not have a mature peripheral T cell phenytype, can proliferate in response to Con A and to IL 2. The ability to establish both short-term and long-term cell lines of Con A- and IL 2-stimulated Thy-1⁺ EC will facilitate analysis of the functional capabilities of these recently recognized cells residing within mouse epidermis.