Dynamic Effects of Thoracic Irradiation on Immune Status of Organs in and out of Radiation Field in Mice

Abstract

Thoracic irradiation involves large blood vessels and hematopoietic tissues which was easily inducing lymphopenia. Lymphocytes are important components of immune response and lymphopenia is associated with poorer survival. However, the dynamic recovery of lymphocyte subsets after thoracic irradiation were rarely reported in the literature. This study focused on dynamic changes of lymphocytes subsets of mice after receiving thoracic irradiation in and out of radiation field. C57BL/6 male mice aged 6-8 weeks received 2Gy*5fx whole thoracic irradiation and were sacrificed on the 1 day, 7 days, 15 days, 25 days after irradiation. Peripheral blood was harvested for mature lymphocyte subsets (B cells, T cells, CD4+T cells, CD8+T cells, NK cells) detection by performing flow cytometry, while thymus, femur bone marrow and sternal bone marrow for hematopoietic stem cells (Long-term Hematopoietic Stem Cell [LT-HSC], Short-term Hematopoietic Stem Cell [ST-HSC]) and progenitor cells (Multipotent Progenitor [MPP], Common Lymphoid Progenitor [CLP]). Absolute counts method was used in flow cytometry and data analysis were performed by scientific 2-D graphing and statistics software. We found that the lymphocyte subsets were significantly reduced in peripheral blood of irradiated mice (all p<0.05). The mature lymphocyte subsets returned to normal 2-3 weeks after irradiation. After radiation, thymus weight was significantly decreased (p<0.0001). With the recovery of thymus weight, the number of hematopoietic stem cells returned to the baseline. For the femur bone marrow (out of the radiation field), hematopoietic stem cells and progenitor cells showed a proliferation tendency. MPP significantly increased in the 1day after irradiation (p = 0.0347) and LT-HSC increased in the 8 days (p = 0.0011). However, although ST-HSC and CLP were slightly increased after irradiation, there were no statistically significance. The sternal bone marrow (in the radiation field) reached the lowest value 1day after irradiation (all p<0.0001). Although hematopoietic stem cells and progenitor cells recovered gradually, but still far away from the level of the control group (all p<0.05). The recovery of lymphocytes in the peripheral blood might mainly come from the supplement of bone marrow out of the irradiation field, while bone marrow in the field suffered serious destruction which did slightly help for lymphocytes recovery.