Langerhans cell interaction with epidermal y& t cells

Two leukocyte populations reside in murine epidermis: a) Langerhans cells (LC), Ag presenting cells of dendritic cell lineage, and b) dendritic epidermal T cells (DETC), tissue-resident y& T cells. Despite their close approximation in vivo, the extent to which LC and DETC affect each other's function is not known. To address this question, we employed the long-term DC line XS52 and the yS T cell line 7-17, both of which were established from mouse epidermis and both of which retain important features of resident LC and DETC. The XS52 cells, which proliferate maximally in response to added GM-CSF or CSF-1, exhibited an equivalent level of proliferation when cocultured with -irradiated 7-17 DETC. Supernatants collected from anti-CD3 stimulated 7-17 DETC cultures, but not from unstimulated cells, also promoted the growth of XS52 cells, suggesting that one or more soluble factors play roles. This supernatant effect was blocked substantially with antibodies against GM-CSF or the receptor for CSF-1, documenting roles for both GM-CSF and CSF-1. Because the 7-17 DETC secreted these cytokines only after stimulation, our observations are most consistent with the hypothesis that XS52 DC deliver activation signals to DETC for the secretion of GM-CSF and CSF-1, which, in turn, promote the growth of XS52 DC. We propose that LC and DETC interact with each other in situ, thereby regulating their residence and function within the epidermal microenvironment.