The focus of the laboratory continues to be cadherin-mediated leukocyte-epithelial interactions, with a major emphasis on understanding E-cadherin-mediated Langerhans cell-keratinocyte adhesion. This novel interaction is important because it influences the ability of Langerhans cells to localize in epidermis, and to emigrate to lymph nodes after activation. Studies of mechanisms that regulate E-cadherin in Langerhans cells have been hampered by the lack of a model system in which to carry out in vitro experiments. We have identified culture conditions that allow propagation of cells that are similar to Langerhans cells, and that will be suitable for studies of E-cadherin function. Dissociated murine d17 fetal skin cells are cultured in media supplemented with GM-CSF and CSF-1. After 10-14 days, aggregates of leukocytes appear and can be separated from adherent stromal cells and contaminating leukocytes. Cells in aggregates resemble Langerhans cells based on morphologic, surface phenotypic and functional criteria, and have the potential to develop into cells that are analogous to lymphoid dendritic cells. Thus, we have established a model system that will permit studies of Langerhans cells in vitro. Recently, we demonstrated that cells in aggregates adhere to each other via an E-cadherin-dependent mechanism, and that they also specifically adhere to other cells that express E-cadherin. In addition, we have determined that biologic response modifiers that activate Langerhans cells in vivo and that mobilize Langerhans cells from murine skin (eg endotoxin and proinflammatory cytokines), dissociate cells in aggregates. Thus, it would appear that E-cadherin function in leukocytes can be regulated via novel mechanisms that are not operative in epithelial cells, and that can be studied in the model system that we have developed. This system will be also useful for other studies of Langerhans cell biology, including studies regarding the role that the pleiotropic cytokine TGFbeta1 plays in dendritic cell ontogeny that are ongoing in the laboratory. We are also interested in the role of wnt genes in cutaneous biology. These studies were initiated because wnt genes are positive regulators of cadherin function, and the drosophila ortholog wingless plays an important role in epidermal development. We have determined that wnt-4 is expressed in murine adult epidermis as well as in murine keratinocytes in vitro. Wnt-4 gene expession is suppressed in keratinocytes treated with mitogeic growth factors and, in preliminary experiments, appears not to be expressed in cells from squamous cell carcinomas. We are now breeding wnt-4 knockout mice and should have additional insights into the importance of wnt-4 gene expression in skin in the near future.
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