The role of tumor necrosis factor alpha (TNF-α) in wound healing is unclear and the results are contradictory. In vivo, TNF-α induces vessel growth, an important step in promoting wound healing. However, a reduced amount of collagen, hydroxyproline, and granulation tissue was found after TNF-α treatment. It is also unknown if this is a direct effect, by influencing cells involved in wound healing, or an indirect effect due to a negative or positive effect on cells such as macrophages.

The current study was undertaken to test the effect of TNF-α on wound epithelialization and neovascularization in vivo. In the first experiment, standardized full-thickness dermal wounds (2.25 mm diameter, 0.125 mm depth) were created on the dorsum of the ears of male hairless mice. The wounds were treated either with TNF-α (100 ng/ml, 1 µg/ml, 5 µg/ml; n = 10 per group), monoclonal TNF-α antibody (10 µg/ml; n = 10), or vehicle (n = 10). Wound epithelialization and neovascularization were analyzed every 3rd day by intravital microscopy until complete healing.

In a second experiment, the same wound model was used, but in order to impair the healing process, macrophages were depleted. To reduce macrophages, two out of four groups (n = 10 per group) were pretreated with iota-carrageenan (MR groups), and the other two groups received only saline (N groups). One N group and one MR group were treated with TNF-α (1 µg/ml). The other N group and MR group received vehicle only (carboxymethylcellulose). Using intravital microscopy and computerized planimetry, wound epithelialization and neovascularization were measured every 3rd day until complete healing. Immunohistochemistry was performed to detect TNF-α, macrophages, fibronectin, and vitronectin receptors.

In the first experiment the wounds treated with 1 µg/ml healed significantly earlier than controls (13.9 ± 2 vs. 17.3 ± 2.8 days, respectively; p < 0.05). Epithelialization in the antibody group was significantly slower compared to controls (20.1 ± 2 days; p < 0.05). Neovascularization was significantly enhanced in the group treated with 1 µg/ml TNF-α (p < 0.05). In the second experiment the wounds treated with TNF-α were significantly earlier epithelialized (13.1 ± 0.6) and vascularized (16.0 ± 0.5) compared to controls (16.8 ± 0.4 vs. 17.6 ± 0.5; p < 0.05). Wound closure was significantly delayed in the MR group treated with vehicle only (20.4 ± 1) and equal to controls in the MR group treated with TNF-α (16.8 ± 0.6).

The results demonstrate the TNF-α accelerates wound epithelialization and neovascularization in this in vivo model. TNF-α is able to compensate for the negative effect of macrophage reduction and seems to have a direct effect on the wound-healing process.