Objective To explore the role of the dendritic cell (DC) antigen presentation CD80/CD28 pathway in radiation-induced T cell activation.
Methods (1) Ninty C57BL/6N mice were randomly divided into the control, irradiation, and irradiation+C6b (a CD80/CD28 inhibitor) groups by using a random number table, 30 mice per group. Mice in the irradiation and irradiation+C6b groups were subjected to a single 20 Gy dose of 60Co γ rays to the thorax. On the basis of irradiation, C6b was dripped into the irradiation+C6b group. Mice from all three groups were sacrificed at one, three, and seven days postirradiation. Single-cell suspensions were prepared from lung draining lymph nodes. The quantities of T cells (CD3+) and their subpopulations (CD4+ and CD8+), as well as the expression of the CD28 and CD69, were assessed by flow cytometry. (2) Mouse lung epithelial cells MLE-12 cells were divided into the control, irradiation, and irradiation+C6b groups. The irradiation group and the irradiation+C6b group were irradiated with 6 Gy 60Co γ rays, while the irradiation+C6b group was supplemented with C6b on the basis of irradiation. After co-cultured 3 groups of MLE-12 cells with spleen derived T cells and (or) bone marrow derived DCs for 6, 12, and 24 hours, the number and activation-related indexes of T cells were detected by flow cytometry. The comparison between the two groups was conducted using a two independent sample t-test.
Results (1) Compared with the control group, the number of T cells (CD3+) and subpopulations (CD4+ and CD8+) in the thoracic lung draining lymph nodes of mice significantly increased on the third day after irradiation ( (1.11±0.12)×105 vs. (3.06±0.35)×105, (0.74±0.06)×105 vs. (1.55±0.12)×105, (0.47±0.05)×105 vs. (0.59±0.06)×105; t=9.128, 10.460, 2.883; all P<0.05). The expression of CD28 on the surface of CD8+ T cell subpopulations significantly increased on the third day after irradiation (238.33±7.09 vs. 310.33±13.32; t=8.169, P<0.05), while the expression of CD69 on the surface of T cell subpopulations (CD4+ and CD8+) significantly increased on the first day after irradiation (96.80±10.74 vs. 207.67±5.77, 67.53±8.29 vs. 125.67±4.51; t=15.750, 10.670; both P<0.05). Compared with the irradiation group, the number of T cells (CD3+) and its subpopulations (CD4+ and CD8+) significantly reduced in the irradiation+C6b group on the third day after irradiation ((3.06±0.35)×105 vs. (1.91±0.12)×105, (1.55±0.12)×105 vs. (1.03±0.08)×105, (0.59±0.06)×105 vs. (0.48±0.03)×105) , and the expression of CD28 and CD69 were significantly decreased on the third day after irradiation (627.00±88.07 vs. 464.00±24.76, 310.00±13.32 vs. 224.00±6.24, 122.33±15.57 vs. 40.87±5.28, 80.97±15.12 vs. 26.97±3.15; t=2.840–10.460; all P<0.05). (2) After 12 h of co-cultured with DCs and T cells, compared with the control group, the numbers of T cells (CD3+) and the subpopulations (CD4+ and CD8+) in the irradiation group of MLE-12 cells increased ((3.87±0.23)×105 vs. (5.57±0.40)×105, (1.58±0.10)×105 vs. (2.31±0.12)×105, (1.96±0.11)×105 vs. (2.83±0.22)×105) and the expression of CD28 and CD69 in T cell subpopulations (CD4+ and CD8+) were significantly upregulated (4.86±0.35 vs. 5.64±0.31, 17.60±0.26 vs. 19.23±0.31, 15.37±2.41 vs. 23.30±0.62, 20.60±1.30 vs. 27.53±2.36), and differences were statistically significant (t=3.067–6.978, all P<0.05). Compared with the irradiation group, the number of T cells (CD3+) and its subpopulations (CD4+ and CD8+) in the irradiation+C6b group were significantly reduced ((5.57±0.40)×105 vs. (3.76±0.13)×105, (2.31±0.12)×105 vs. (1.66±0.06)×105, (2.83±0.22)×105 vs. (1.83±0.01)×105), the expression of CD28 and CD69 in T cell subpopulations (CD4+ and CD8+) were significantly reduced (5.64±0.31 vs. 4.63±0.34, 19.23±0.31 vs. 15.87±1.04, 23.30±0.62 vs. 17.93±1.90, 27.53±2.36 vs. 20.67±0.84), and differences were statistically significant (t=3.802–8.307, all P<0.05).
Conclusion The DC antigen presentation CD80/CD28 pathway partially mediates radiation-induced T cell activation.
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