Research On The Pathological Features And Mechanism Of Immune Tissue Injury Radiated By Neutron

Objective: Immune organs are highly sensitive to ionizing radiation, with heavy injuries, slow recovery and difficult to cure. The damage mechanisms remain unclear, and there is no effective prevention and cure measure. As the conditions of neutron irradiation required highly and the animal models of neutron damage were difficult to establish, the characteristics and patterns of injures caused by different doses of neutrons on the immune tissue have yet to be clarified. Based on previous findings, this article studied the mechanism of immune injury by neutron radiation from two aspects of cell apoptosis and Th1/Th2 imbalance, and then explored the application of rhIL-11 treatment. This study further clarified the pathological characteristics, rules, mechanisms and preventions of immune injury caused by neutron, and had important significances.Materials and methods: 90 male BALB/c mice were randomly divided into control group, 3 Gy neutron irradiation group and rhIL-11 treatment group, with 30 rats every group. The mixing ratio of neutron andγ-ray was 9:1 and absorbed dose was 3.0 Gy. RhIL-11 was used by intraperitoneal injection with 600μg/kg/d and daily administration. The mice were sacrificed at 6h, 1d, 3d and 5d after irradiation. The effects of neutron irradiation on mice spleen and thymus morphology and the cure effects of rhIL-11 on immune function injury by neutron irradiation were studied systematically by peripheral blood lymphocyte counts, weight index, light and electron microscopic from the general, tissues, cells and sub-cellular levels, and further to detect apoptosis, the expression of caspase 3, IL-2 and 4 by in situ end labeling, immunohistochemistry to investigate the mechanism of immune tissue injury caused by neutron radiation.Results: 1. The changes of white blood cell and lymphocyte count after 3Gy neutron irradiation: during 3d after 3Gy neutron irradiation, the WBC and lymphocyte counts were significantly lower than control group, and decreased continuously.2. The changes of spleen and thymus weight index after 3Gy neutron irradiation: during 3d after neutron irradiation, thymus and spleen weight index was significantly lower than the control group, and decreased continuously.3. The pathological changes of thymus and spleen after 3Gy neutron irradiation: (1) The pathological changes of thymus: a large number of lymphocyte appeared apoptosis or necrosis at 6h after irradiation. The number of lymphocytes reduced significantly at 1d, with dead cells and a small amount of nuclear debris. The number of lymphocytes reduced extremely and the number of reticular cells and fibroblasts increased at 3d. The thymus lymphoid tissue occurred regeneration mainly in the cortical area around the small arteries at 5d. (2) The pathological changes of the spleen: A large number of lymphocytes were apoptosis or necrosis and necrotic cells was more prevalent at 6h after irradiation. The number of lymphocytes reduced significantly with occasionally apoptotic cells and a small amount of nuclear fragmentation, nuclear dissolution at 1d. The number of lymphocytes reduced extremely at 3d, and the nuclear fragments of varying sizes is still seen, and the number of plasma cells, reticular cells and fibroblasts increased. The lymphoid tissue was regenerated and repaired at 5d. (3) The ultrastructural changes: at 6h after 3Gy neutron irradiation, the apoptosis and necrosis co-exist in lymphocytes of thymus and spleen, showing nuclear chromatin condensation, side shift, half-moon changes, apoptotic body formation and nuclear fragmentation and nuclear dissolution prevalent.4. The results of cell apoptosis of thymus and spleen detected by in situ end labeling after 3Gy neutron irradiation: The results of thymus and spleen were similar, which was that the numbers of apoptotic cells were significantly more than the control group at 6h and 1d after irradiation. The apoptosis cells had no significant difference with control group at 3d. 5. The changes of caspase3 expression of thymus and spleen after 3Gy neutron irradiation: (1) Spleen: white pulp area shows a large number of strongly positive cells, mainly lymphocytes at 6h after irradiation. Only a small number of positive lymphocytes could be seen at 3d and 5d. The MOD and IOD of caspase3 expression were significantly higher than other groups. (2) Thymus: the cortex shows a large number of strongly positive cells, mainly lymphocytes at 6h and 1d after irradiation. Only a few positive lymphocytes could be seen at 3d and 5d.6. The expression of IL-2 in spleen after 3Gy neutron irradiation: White pulp and red pulp area shows a large number of strongly positive cells, mostly lymphocytes and macrophages at 6h after irradiation. The MOD and IOD of IL-2 expression were significantly higher than other groups. The positive cells were significantly reduced, and mainly macrophages at 1d, 3d and 5d.7. The expression of IL-4 in spleen after 3Gy neutron irradiation: There were a large number of positive cells in spleen white pulp and red pulp of control group, including lymphocytes, macrophages and giant cells, etc. The positive cells decreased and the expression was decreased at 6h and 1d after irradiation. The positive cells increased and positive enhanced at 3d. The MOD and IOD of IL-4 expression were significantly lower than control group at different time point's after 3Gy neutron irradiation.8. The effects of rhIL-11 therapy on peripheral blood and lymphocyte count after irradiation: Leukocyte and lymphocyte count and lymphocyte percentage in treatment group was significantly lower than control group at 3d and 5d after rhIL-11 treatment, but there was no significant difference between treatment group and irradiation group. There was no significant difference at 3d and 5d in treatment group.9. The changes of rhIL-11 therapy on of thymus and spleen weight index after irradiated: The changes in thymus and spleen index were similar: the treatment group was significantly lower than the control group at 3d and 5d after rhIL-11 treatment, but compared with the irradiation compared with no significant difference.10. The effects of rhIL-11 therapy on morphology of thymus and spleen after irradiation: (1) Thymus: the cortex appears lymphoid tissue regeneration, mainly in the small arteries around at 3d and 5d after rhIL-11 treatment. (2) Spleen: white pulp lymphoid tissue appears regeneration area, the increasing number of small arteries around the lymphocytes at 3d and 5d after rhIL-11 treatment.Conclusion:1. 3.0 Gy neutron irradiation can cause destruction of the spleen and thymus morphology: (1) the characteristics and laws of the lesion: lymphocyte injury manifested as apoptosis or necrosis, mainly necrosis. The apoptosis and necrosis of thymic cortex lymphocytes were more severe than the medulla, and the apoptosis and necrosis of splenic white pulp cells were more severe than the red pulp. The damage of lymphocytes appeared earlier and progress rapidly after irradiation. The cells regeneration occurs earlier. (2) pathological staging: apoptosis and necrosis stage of lymphocyte; residue depletion stage of lymphocyte; regeneration stage of lymphocyte.2. Apoptosis is one of the important ways to die of immune tissue injuries induced by neutron irradiation. Caspase 3 plays a regulatory role in the apoptosis of lymphocytes induced by neutron irradiation.3. Neutron irradiation leading to Th1 and Th2 type cytokine imbalance: an early advantage for the Th1-type response with cellular immunity-based leaded to tissue and cell damage. Late advantage for the Th2-type response with humoral immune-based suppressed the immune inflammation and reduced the over-injury.4. RhIL-11 has some therapeutic effect on immune tissue injury induced by neutron irradiation.