Function of human skin T cells in wound healing in the in vitro experimental setting

Currently, the treatment of persistent non-healing wounds is among the most difficult clinical issues. We studied 20 samples of normal human skin, 10 specimens from patients with acute trauma, and 9 samples from the patients with chronic wounds that did not heal within 2 months. Using multicolor flow cytometry, we found that the resident T lymphocytes (CD3⁺αβ⁺ and CD3⁺γθ⁺) are able to locally produce biologically active substances, normalize human skin homeostasis, thus promoting the wound healing. The data obtained indicate that the blood contains mainly αβ⁺T lymphocytes (p < 0.001), while the γθ⁺T cells detected in wounds represent a population similar to skin cells. We found no difference in the ratio of resident T cells in chronic and acute wounds, and healthy epithelium. Accordingly, non-healing of wounds and chronic clinical course may be caused by dysfunction of T cells. CD69 regulates γθ T cell secretion of growth factors, IFNγ, IL-17 and IL-22. The relative number of CD69-expressing T cells from the patients with acute wounds was significantly increased, if compared with cells from normal epidermis and chronic wounds (10.5%±2.3, 7.6%±1.24, and 3.0%±1.05, respectively. p < 0.001). The number of cells with the CD3⁺αβ⁺CD69⁺ phenotype did not differ significantly between all three groups under comparison. Dysregulation of T cell-mediated healing in chronic wounds is caused by reduced production of IGF-1 by resident CD3⁺αβ⁺T lymphocytes (1.7%±0.9 (p < 0.001), and CD3⁺γθ⁺ (0.44%±0.02, p < 0.001) compared to CD3⁺αβ⁺T cells derived from acute wounds (13.6%±5.6) and CD3⁺γθ⁺ (8.9%±3.1). The αβ⁺ and γθ⁺ T cells isolated from non-healing chronic wounds did not respond to mitogenic stimuli, unlike the cells obtained from acute wounds and healthy skin. In vitro analysis of cytokine secretion by the CD69-deficient dermal γθ T cells showed a lower spontaneous secretion of IL-22 (4.56%±2.3 and 23.9%±1.05 and 10.6%±1.24, respectively; p < 0.001) and IL-2 (0.9%±0.08 and 22.6%±2.5 and 3.9%±1.0, and respectively; p < 0.01). When analyzing the number of resident γθ skin T cells secreting IL-17, we obtained the following differences for healthy skin (1.4%±0.08), acute wounds (11.3%±3.2) and chronic wounds (31.7%±11.8), thus showing a significant intergroup difference (p < 0.001). T lymphocytes in chronic wounds exhibit some functional disorders and are not able to produce biologically active substances that promote physiological tissue regeneration. The results suggest a role of resident T cells in human skin in wound healing processes and provide new insights into the pathogenesis of chronic wounds.