Purpose: Study the apoptotic death of peripheral blood lymphocytes in long-term period in persons exposed to chronic radiation exposure, and analysis of association of the polymorphic regions rs4645878, rs2279115, rs28362491, rs664677, rs1042522, rs1801270, rs2279744 of the BAX, BCL2, NFkB, ATM, TP53, CDKN1A, MDM2 genes with apoptotic lymphocytes frequency in residents of the coastal villages of the Techa River. Material and methods: The study of apoptosis and genotyping was conducted in 390 persons exposed to chronic radiation exposure as a result of Mayak PA radioactive waste releases into the Techa–Iset–Tobol river system. The early stage of apoptosis was assessed on a flow cytometer by the presence of phosphatidylserine on the surface of the cell membranes using the Annexin V Apoptosis Detection Kit I and the late stage of apoptosis using the TUNEL method. Real-time PCR genotyping was performed of allelic variations of rs4645878, rs2279115, rs28362491, rs664677, rs1042522, rs1801270, rs2279744 of BAX, BCL2, NFkB, ATM, TP53, CDKN1A, MDM2 genes in a group of irradiated individuals. Results: The number of cells at the early stage of apoptosis is statistically significantly increased in individuals whose irradiation began during the period of intrauterine development and continued in the postnatal period compared to individuals exposed only in the postnatal period. At the same time, the number of lymphocytes at the stage of DNA fragmentation in the group irradiated in utero is lower than in the group irradiated postnatally and non-irradiated individuals. Also, a weak negative correlation between intrauterine doses of RBM irradiation and the doses of thymus and peripheral lymphoid organs with the number of cells in the late stage of apoptosis in individuals irradiated in utero. The influence of allelic variation rs4645878 of the BAX gene was established on the number of lymphocytes at the early stage of apoptosis in residents of coastal villages of the Techa River. A statistically significant decrease in the number of cells at an early stage of apoptosis is observed in C/C genotype carriers according to the allelic variation rs4645878 of the BAX gene compared with carriers of the T/T and T/C genotypes. Conclusion: Residents of coastal villages of the Techa River exposed to radiation during the period of prenatal development, there are differences in the frequency of apoptotic death of peripheral blood lymphocytes compared with non-irradiated persons and persons who were irradiated in the postnatal period. SNPs of apoptosis-regulating genes can modify the response of blood lymphocytes to radiation in a wide range of doses RBM.

Transcriptional activity of genes involved in maintaining genetic homeostasis (genes for repair, cell cycle and apoptosis: TP53, MDM2, ATM, BAX, BCL-2, CDKN1A, OGG1, XPC, PADI4, MAPK8, NF-KB1, STAT3, GATA3) was studied in chronically exposed persons with an increased intensity of early and late stages of apoptosis and necrosis of peripheral blood lymphocytes. The object of this study was peripheral blood mononuclear cells obtained from 132 chronically exposed residents of the Techa riverside villages. The mean accumulated dose to red bone marrow was 426.4±48.2 mGy (1.3–2930.0 mGy), to thymus and peripheral immune organs, 58.9±7.9 mGy (0.1–489.0 mGy). The study was performed more than 60 years after the onset of exposure, the average age of exposed persons was 68±0.6 years (55–86 years). The study of apoptotic and necrotic death of peripheral blood lymphocytes was based on the presence of phosphatidylserine on the cell membrane surface, as well as on its permeability for DNA-intercalating dye. Evaluation of the relative content of mRNA genes for repair, cell cycle, and apoptosis was carried out using real-time PCR. An increased relative content of PADI4 gene mRNA was registered in the group of chronically exposed persons with the increased intensity of early apoptosis (p = 0.006). Modulation of the relative content of mRNA of the TP53 (p = 0.013) and BCL-2 (p = 0.021) genes was detected in the group of chronically exposed individuals with the increased intensity of the late stage of apoptosis. A statistically significant increase in the transcriptional activity of the TP53 gene was observed in the group of chronically exposed persons with the increased intensity of peripheral blood lymphocyte necrosis in the long-term period (p = 0.015). In the course of the study it was noted that exposed people with increased intensity of apoptosis, first of all, demonstrate changes in the transcriptional activity of apoptotic genes. These data are consistent with current views on the activation of programmed cell death.

Earlier, it has been convincingly established that exposure to ionizing radiation (IR) alters the T cell-mediated immunity in the long term. However, a search for papers describing the effect chronic exposure to radiation has on various subpopulations of T-helpers yielded no results. Therefore, we designed this study seeking to investigate the quantitative characteristics of various subpopulations of T-helpers in the peripheral blood of individuals chronically exposed to low-level radiation for a long period of time. The study involved 102 chronically exposed Techa Riverside residents (Russia) aged 60–87 years. The participants were divided into two groups, one comprised of exposed individuals with the average red bone marrow (RBM) irradiation dose of 567 ± 73 mGy, another, the control group, comprised of people with the irradiation dose below 70 mGy. With the help of flow cytometry, we identified the quantitative characteristics of T-helper subpopulations in the peripheral blood at various stages of their differentiation, as well as various T-helper subpopulations of central and effector memory. The study revealed no significant differences in the composition of T-helper subpopulations in the compared groups. We discovered a significant growth of the double positive follicular T-helper 17 subpopulation in the population of central memory T-helpers, which is associated with the increase of RBM (p = 0.04; S = 0.19), thymus and peripheral lymphoid organs (p = 0.03; S = 0.22) irradiation dose. In the group of exposed individuals, the number of naive T-helpers (p = 0.009) and double positive follicular T-helpers 17 in the TEM subpopulation (p = 0.04) was decreasing as the age of participants increased, and the number of effector memory T-helpers, on the contrary, increased with age (p = 0.04). We have not registered similar phenomena in the comparison group.

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Changes in the peripheral blood cellular composition were observed in the long term period in the residents of the Techa riverside villages chronically exposed to radiation, which may be the consequence of structural and functional disorders in the pool of hematopoietic stem cells (HSC) and progenitor cells. Therefore, the study was aimed to quantify peripheral blood CD34+ cell pool in individuals chronically exposed to radiation over a long-term period. Sixty years after the onset of exposure, a total of 153 individuals were examined, who were divided into four groups: individuals exposed in utero and postnatally (the average postnatal absorbed dose was 570 mGy); individuals exposed only postnatally (the average postnatal absorbed dose was 790 mGy), and two comparison groups, in which the average postnatal absorbed dose to red bone marrow did not exceed 70 mGy. Absolute and relative peripheral blood CD34+ cell counts in chronically exposed individuals were assessed by flow cytometry. No changes in CD34+ cell counts compared to comparison group were revealed in the group of individuals exposed in utero and postnatally; no age-related changes were registered as well. However, a significant decline in absolute HSC and progenitor cell counts with increased absorbed dose to red bone marrow was observed. In the group of individuals exposed only postnatally, there was a significant increase in peripheral blood CD34+ cell counts compared to comparison group (p = 0.004 for absolute cell count; p = 0.009 for relative cell count), dose-dependent increase in peripheral blood HSC and precursor cell counts (p = 0.02 for absolute cell count; p = 0.03 for relative cell count), along with age-related decline in these cells’ counts (р = 0.02 for absolute cell count; p = 0.04 for relative cell count).