Neutrophils express tumor necrosis factor-alpha during mouse skin wound healing.

The expression pattern of tumor necrosis factor-alpha (TNF-alpha) mRNA and protein was examined in vivo in experimental mouse skin wounds by in situ hybridization and immunohistochemistry. TNF-alpha mRNA and protein is detected in a distinct layer of mainly neutrophils subadjacent to the would clot. The layer of TNF-alpha-positive cells extends from the margin of the advancing epithelial outgrowth to the opposing one. By in situ hybridization the TNF-alpha mRNA is detectable 12 h after wounding; the signal peaks after 72 h and remains visible up to at least 120 h after wounding. TNF-alpha mRNA could not be detected in the normal skin or in 5-hour-old wounds. Immunohistochemical staining for TNF-alpha and macrophages on adjacent sections confirms that the main part of TNF-alpha-positive cells are polymorphonuclear neutrophils and shows that most of the cells located just beneath the layer of TNF-alpha-positive neutrophils are macrophages with weak TNF-alpha immunoreactivity. The data reported here show that neutrophils serve as an important source of TNF-alpha during healing of mouse skin wounds. We suggest that this specific expression of TNF-alpha is related to the process of re-epithelialization.