Effects of dendritic epidermal T cells on proliferation and apoptosis of epidermal cells in wound margin of mice

Objective To explore the effects of dendritic epidermal T cells (DETC) on proliferation and apoptosis of epidermal cells in wound margin of mice and its effects on wound healing. Methods Twenty-eight healthy specific pathogen free (SPF) C57BL/6 wild-type (WT) male mice aged 8-12 weeks and 60 SPF T lymphocyte receptor δ-knockout (TCR δ^-/-) male mice aged 8-12 weeks were selected to conduct the following experiments. (1) Eight WT mice were selected to isolate epidermal cells and primarily culture DETC according to the random number table. Morphological observation and purity identification of DETC by flow cytometer were detected immediately after culture and on culture day (CD) 15 and 30, respectively. (2) According to the random number table, 5 WT mice and 5 TCR δ^-/- mice were selected and enrolled into WT control group and TCR δ^-/- group. Round full-thickness skin defect with diameter of 6 mm was made on the back of each mouse. The wound healing condition was observed immediately after injury and on post injury day (PID) 2, 4, 6, 8, 10, and the percentage of residual wound area was calculated. (3) Mice were selected to group and reproduce model of full-thickness skin defect as in experiment (2). On PID 3, the tissue of wound margin was collected for hematoxylin eosin staining, and the length of new epithelium was measured. (4) Mice were selected to group and reproduce model of full-thickness skin defect as in experiment (2). On PID 3, epidermal tissue of wound margin was collected to determine expression of proliferating cell nuclear antigen (PCNA) using Western blotting for evaluation of proliferation of epidermal cell. (5) Mice were selected to group and reproduce model of full-thickness skin defect as in experiment (2). On PID 3, epidermal tissue of wound margin was selected and digested into single-cell suspension, and apoptosis of cells was detected by flow cytometer. (6) Forty TCR δ^-/- mice were selected to carry out the same treatment as in experiments (2)-(5). According to the random number table, these mice were enrolled into TCR δ^-/- control group and TCR δ^-/-+ DETC group, with 5 mice in each group for each experiment. Round full-thickness skin defect was made on the back of each mouse. DETC in the number of 1×10⁵ (dissolution in 100 μL phosphate with buffer purity above 90%) were injected through multiple points of wound margin of mice in TCR δ^-/-+ DETC group immediately after injury, and equal volume of phosphate buffer was injected into mice of TCR δ^-/- control group with the same method as above. Data were processed with one-way analysis of variance for repeated measurement,

test, and Bonferroni correction. Results (1) Along with the culture time elapse, the number of dendritic structures of DETC increased gradually. The percentage of T lymphocytes was 4.67% and 94.1% of these T lymphocytes were DETC. The purity of DETC on CD 15 was 18.50% and the purity of DETC on CD 30 was 98.70%. (2) Immediately after injury, the wound healing condition of mice in WT control group and TCR δ^-/- group was similar. The wound healing speed of mice in TCR δ^-/- group was slower than that in WT control group on PID 2-10. The percentages of residual wound area of mice in TCR δ^-/- group on PID 2, 4, 6, 8, and 10 were increased significantly compared with those in WT control group (

=3.492, 4.425, 4.170, 4.780, 7.318,

<0.01). (3) The length of new epithelium of mice in TCR δ^-/- group on PID 3 was (359 ± 15) μm, which was obviously shorter than that in WT control group [(462±26) μm,

=3.462,

<0.01]. (4) Immediately after injury, wound condition of mice in TCR δ^-/-+ DETC group and TCR δ^-/- control group was similar. Compared with TCR δ^-/-+ DETC group, the wound healing speed of mice in TCR δ^-/- control group were obviously slower on PID 2-10. The percentages of residual wound area of mice in TCR δ^-/-+ DETC group on PID 2, 4, 6, 8, and 10 were decreased significantly compared with those in TCR δ^-/- control group (

=2.308, 3.725, 2.698, 3.707, 6.093,

<0.05 or

<0.01). (5) On PID 3, the length of new epithelium of mice in TCR δ^-/-+ DETC group was (465±31) μm, which was obviously longer than that in TCR δ^-/- control group [(375±21) μm,

=2.390,

<0.05]. (6) On PID 3, PCNA expression of epidermal cell in wound margin of mice in TCR δ^-/- group was 1.25±0.04, which was obviously lower than that in WT control group (2.01±0.09,

=7.415,

<0.01). (7) On PID 3, PCNA expression of epidermal cell in wound margin of mice in TCR δ^-/-+ DETC group was 1.62±0.08, which was significantly higher than that in TCR δ^-/- control group (1.05±0.14,

=3.561,

<0.05). (8) On PID 3, apoptosis rate of epidermal cell in wound margin of mice in TCR δ^-/- group was (16.1±1.4)%, which was higher than that in WT control group [(8.1±0.6)%,

=5.363,

<0.01]. (9) On PID 3, apoptosis rate of epidermal cell in wound margin of mice in TCR δ^-/-+ DETC group was (11.4±1.0)%, which was obviously lower than that in TCR δ^-/- control group [(15.4±1.4)%,

=2.377,

<0.05]. Conclusions DETC participates in the process of wound healing though promoting the proliferation of epidermal cells in wound margin and inhibit the apoptosis of these cells.