Effect of fractionated radiotherapy of transplanted hepatocellular carcinoma on the splenic immune cells in mice

Objective To investigate the effect of fractionated radiotherapy on the immune system of mice with subcutaneously transplanted hepatocellular carcinoma. Methods Logarithmic growth of mouse hepatocellular carcinoma cells Hepa 1-6 were inoculated subcutaneously on the right side of C57BL/6 J mice (1×107 cells /mice). The tumor-bearing mice were randomly divided into control group (Ctrl) and irradiation group (IR), 20 mice in each group. Additionally, 10 healthy mice were set as normal control group. Local fractionated X-ray irradiation of 8 Gy×3 fraction was given to the subcutaneous tumors, and the dose rate was 0.883 Gy/min. At 7 and 14 d after irradiation, the tumor organ index, spleen organ index, spleen pathological changes, and splenic T lymphocyte subsets, B lymphocyte subsets, and NK cells were detected. Results Compared with Ctrl, at 7 and 14 d after irradiation, the tumor organ index decreased (t=4.649, 26.34, P<0.05), and the percentage of NK cells increased significantly (t=3.952, 3.633, P<0.05). The percentages of CD3+ , CD4+ , CD3+ CD4+ lymphocytes and the ratio of CD4+ /CD8+ lymphocyte decreased at 7 d after irradiation (t=3.193, 3.656, 3.219, 2.641, P<0.05), and the percentage of CD3+ lymphocyte decreased at 14 d after irradiation (t=3.031, P<0.05). But after irradiation, there were no significant changes in spleen organ index, B lymphocyte, CD3+ CD4+ lymphocyte and CD8+ lymphocyte. Conclusions Local hepatoma radiotherapy causes imbalance of lymphocytes in distal spleen of mice and hence reduces immunity, which provides a novel mechanism of radiological immunity damage. Key words: Hepatocellular carcinoma; Fractionated radiotherapy; Splenic lymphocytes