Results of studying pro- and anti-atherogenic immune factors in the persons chronically exposed to ionising radiation

It is well established that cohorts of individuals exposed to ionizing radiation exhibit increased risks for cardiovascular diseases. Currently, the role of immune system in pathogenesis of atherosclerosis is actively studied. Meanwhile, the immunomodulatory effects of irradiation in pathogenesis of atherosclerosis in the persons exposed to ionizing radiation still remain unclear. The aim of this research was to study the effect of ionizing radiation upon lymphocyte subpopulations involved in pathogenesis of atherosclerosis. The lymphocyte subpopulations were studied in peripheral blood of the workers chronically exposed to occupational combined radiation versus a control group. The study considered 72 workers of the Russian nuclear production facility, the Mayak Industrial Association (mean age of 72.1±10.9 years), and 72 control individuals (mean age of 70.7±9.2 years). All the workers were chronically exposed to combined radiation (external gamma-rays and internal alpha-particles). The mean cumulative dose absorbed by red bone marrow from external gamma-ray exposure was 0.750±0.699 Gy; the mean cumulative absorbed dose to red bone marrow from internal alpha-particles was 0.072±0.092 Gy. The relative and absolute numbers of lymphocyte subpopulations (total T-cells, T-helpers, T-cytotoxic, total B-cells, NK-cells and T-NK-cells) were detected by flow cytofluorometry. The absolute number of CD3 + CD19 + T-lymphocytes was significantly lower in the individuals exposed to chronic irradiation, compared with the controls (1658.8±694.3 x 10 6 /l and 1988.4±1045.4 x 10 6 /l, respectively). The relative number of CD3 + CD4 + T-helpers and CD3 + CD8 + T-cytotoxic lymphocytes was significantly higher in individuals exposed to chronic irradiation. Relative number of T-helpers in the main group was 42.4±8.8% vs 35.3±8.7% in controls; the relative number of T-cytotoxic lymphocytes was 27.6±9.5%, and 23.3±6.5%, respectively. A significant negative correlation was revealed between absolute number of T-lymphocytes and cumulative absorbed doses to bone marrow from external gamma irradiation (correlation quotient r = -0,53565, p = 0,000001) and internal alpha sources (r = -0.54804, p = 0.0000006). This correlation may indicate a relationship between these changes (decreased absolute numbers of T cells) and occupational exposure rates. The increased relative number of T-helpers and cytotoxic T-lymphocytes confirm an assumption that specific antigens may cause an enhanced immune response during the development of atherosclerosis in exposed individuals.