Intradermal transgenic expression of granulocyte-macrophage colony-stimulating factor induces neutrophilia, epidermal hyperplasia, Langerhans' cell/macrophage accumulation, and dermal fibrosis.
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Granulocyte-macrophage colony-stimulating factor (GM-CSF), a pleiotropic cytokine, is up-regulated in a number of chronic skin inflammatory diseases, particularly atopic dermatitis. However, its role in these conditions remains largely unclear. To explore its function, we have established a rat intradermal transgene model by using a replication-deficient adenoviral vector expressing GM-CSF. Intradermal GM-CSF gene transfer led to a prolonged compartmentalized expression of transgene protein in the dermis. This expression induced an unexpectedly wide spectrum of pathologies in both epidermis and dermis, including neutrophilia, epidermal hyperplasia (acanthosis), an increased number of epidermal Langerhans' cells, accumulation of MHC II-positive macrophages, as well as mild eosinophilia in the dermis at earlier stages and upper dermal fibrosis at later stages. These findings thus identify GM-CSF as a potent multifunctional cytokine at skin site that is capable of evolving numerous inflammatory processes ranging from the early acute neutrophilia to later chronic fibrotic responses, and also suggest the important role of this cytokine in the development and perpetuation of pathologic changes in chronic skin inflammatory conditions including chronic atopic dermatitis. In addition, our study presents a novel model of adult normal animals that is useful for identifying and studying key cytokines involved in inflammatory skin diseases.
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