IL-17C and IL-17RE Promote Wound Closure in a Staphylococcus aureus-Based Murine Wound Infection Model

Abstract

The epithelial cytokine interleukin-17C (IL-17C) mediates inflammation through the interleukin 17 receptor E (IL-17RE). Prior studies showed a detrimental role of IL-17C in the pathogenesis of immune-mediated skin diseases (e.g., psoriasis). Here, we examined the role of IL-17C/IL-17RE in wound closure in a Staphylococcus aureus wound infection model. We demonstrate that wound closure is significantly delayed in IL-17RE (Il-17re^-/-)- and 17C (Il-17c^-/-)-deficient mice. There was no significant difference between WT, Il-17re^-/-, and Il-17c^-/- mice in the absence of infection. Deficiency for IL-17RE and IL-17C did not significantly affect the elimination of bacteria. IL-17C expression was increased in the epidermis of human S. aureus-infected skin. Our results indicate that the IL-17C/IL-17RE axis contributes to the closure of infected wounds but does not contribute to the elimination of S. aureus.

Keywords: Staphylococcus aureus; interleukin-17C; wound closure; wound infection.

Figure 1

The deficiency for IL-17C and IL-17RE results in a delayed closure of infected wounds. Wounds were introduced into the flanks of WT (red symbols), Il-17c^−/− (green symbols) and Il-17re^−/− (blue symbols) mice and infected with 10⁵ CFU of S. aureus strain Newman (filled symbols) or PBS (open symbols) as control. (a) The averaged wound areas (mm²) are shown 0, 2, 4, and 6 days after wounding (n = 12–14 per group). Each symbol represents an individual wound. Horizontal bars indicate the median of all observations. Data were compared by a two-way ANOVA and Holm–Sidak’s post hoc test. * p < 0.05; ** p < 0.01; *** p < 0.001; ns, not significant. (b) Representative images of wounds 6 days after wounding. Scale bar, 2 mm.

Figure 2

The deficiency for IL-17C and IL-17RE does not affect the bacterial load and PMN content of S. aureus-infected wounds. (a) Numbers of viable bacteria (CFU) in wounds of WT (red symbols), Il-17c^−/− (green symbols) and Il-17re^−/− (blue symbols) mice at 6 days post-infection. (b) Representative images of hematoxylin–eosin (H&E)-stained tissue sections obtained from S. aureus-infected wounds of wild-type and IL-17c^−/− mice at 6 days post-infection. Scale bar, 100 µm. (c) Numbers of PMNs in the dermal regions of the infected wounds (n = 6–8 per group). (d,e) Concentrations of KC (d) and MIP-2 (e) in wound homogenates of 6-day-old S. aureus-infected wounds (n = 14 per group). (f) Representative images of CD68-stained tissue sections obtained from S. aureus-infected wounds of wild-type and IL-17c^−/− mice at 6 days post-infection. Scale bar, 100 µm. (g) Numbers of CD68⁺ cells in the dermal regions of the infected wounds (n = 6–8 per group). Each symbol represents an individual wound. Horizontal bars indicate the median of all observations. Data were compared by a one-way ANOVA and Holm–Sidak’s multiple comparison test (a,d,e) or the unpaired Student’s t-test (c). ns, not significant.

Figure 3

The deficiency for IL-17C and IL-17RE does only marginally affect the contents of wound-healing-associated cytokines in S. aureus-infected wounds. (a–d) Concentrations of G-CSF (a), IL-6 (b), IL-17A (c), and TNF-α (d) in wound homogenates of 6 days old S. aureus-infected wounds (n = 14 per group). (e) Ki-67 proliferation indices of tissue sections obtained from S. aureus-infected wounds of wild-type and IL-17c^−/− mice at 6 days post-infection (n = 5–7). (f) Representative images of K5-stained tissue sections obtained from S. aureus-infected wounds of WT and IL-17c^−/− mice at 6 days post-infection. Scale bar, 1 mm. (g) Intensity scores of K5-positive cells in the epidermal regions of the infected wound edges (n = 6–8 per group). Each symbol represents an individual wound. Horizontal bars indicate the median of all observations. Data were compared by one-way ANOVA and Holm–Sidak’s multiple comparison test (a–d) or the unpaired Student’s t-test (e,g). ns, not significant; * p < 0.05; ** p < 0.01.

Figure 4

IL-17C is expressed in S. aureus-infected skin (a,b). IL-17C was detected by immunohistochemistry in formalin-fixed, paraffin-embedded skin samples obtained from 3 non-infected individuals (a) and 5 patients with S. aureus skin infection (b). Scale bar, 100 µm. (c) The relative IL-17C intensity was quantified in the epidermis and dermis in relation to the staining intensities seen with hematoxylin in the respective regions. Relative IL-17C intensities between non-infected (black symbols) and S. aureus infected (red symbols) wound biopsies were compared by unpaired Student’s t-test. **, p < 0.01.