Study On Immune Function And DNA Damage Level Of Long - Term Low Dose Ionizing Radiation

BackgroundImmune effect induced by low dose ionizing radiation is one of the important direction of health effects on low dose radition research. Lots of animal experiments confirmed that low dose ionizing radiation could stimulate immune effects through augmenting the proliferative reactive response of T cells, encouraging the development of Thl cells and secreting IL-2SC,but the epidemiological studies about this aspect are rare and the results are not consistent. United Nations Scientific Committee on The Effects of Atomic Radiation (UNSCEAR) 2012 report indicates that radiation-induced perturbation of immune function or induction of inflammatory reactions based on the study of cytokines levels and T lymphocyte subsets of atomic-bomb survivors, and suggests further study. Immune function can be evaluated by estimating changes of cell numbers or by cytokines level, there is no one single end-point for measuring and reflecting immune function comprehensively. Antibody microarray appeared in 2000 can stimulatory detect hundreds of cytokines, which has an important meaning to discover cytokines profiles and explore the relationship of cytokines. Besides, the telomere study of low dose radiation is a hot issue, can help explain DNA damage level after low-dose irradiation.PurposeThis study is aimed to explore immune function after long-term low dose radiation through detecting the levels of peripheral blood lymphocyte subsets and serum cytokines of uranium miners and residents lived in Yangjiang high background radiation area, and to observe DNA damage level by measuring telomere length, which can evaluate health effects of the population exposed to low dose radiation for providing direct observation and show the scientific basis for solving practical problems in radiological protection practice.Methods1. Forty-nine workers were selected from a uranium mine and classified the miners into two groups. Exposed group included 28 male miners continuously working underground for≥5 years, and control group included 21 male persons who continuously worked underground for<5 years. Customized antibody microarrays were used to detect 50 cytokines or receptors in sera of uranium miners.2. Flow cytometry was used to detected peripheral blood T lymphocyte and its subsets (CD4+T, CD8+T lymphocyte) in 100 healthy female residents selected from Yangjiang high background radiation area (HBRA) and control area (CA), respectively.3. Forty subjects were selected from 200 residents mentioned above based on age and BMI matched between two groups,30 cytokines or receptor (based on the past study and cytokines expression of uranium miners) and CRP (vascular inflammatory markers) levels were measured using antibody arrays, and then verify the cytokines expression in profiles using ELISA methods, including IL-la, IFN-y, MCP-1 and IL-6sR, EGFR, CRP. Telomere length in peripheral blood of 80 healthy residents was measured by real-time PCR.4. Comparing difference of T lymphocyte subsets, cytokines absolute concentration and telomere length between two groups using independent sample t-test. Significance analysis of microarray (SAM) was used to choose significant regulated cytokines, any increase equal or larger than 1.5-fold or decrease equal or lesser than 0.65-fold in signal intensity for a single cytokine between two groups is considered significant difference in expression. The significant difference is indicated by q-value<0.05, and dose-response relationship and effectsize of influence factors using multiple or multivariate linear regression analysis.Results1. The difference of age distribution, body mass index (BMI) between two groups is no statistic significance. Of the 50 custom cytokines and receptors,28 cytokines were measurable. Compared to control group, the release of IP-10, IL-1a, IL-1sRI, IL-3, IL-15 were significantly up-regulated, fold change is 1.78,1.71,1.65,1.62,1.59, q-values<0.05. Other pro-inflammatory cytokines such as IL-2, IFN-γ, IL-10, IL-6, TNF-α levels were slightly up-regulated. With adjustment to age and BMI, IL-1α and IL-3 levels increased significantly with underground time, IL-1α and IL-3 relative levels increases 31%,36%per 10 years, respectively. The effectsize of IL-1α and IL-3 levels attributed to dose is 0.16,0.11.2. The mean cumulate dose in HBRA and CAis 163.83±37.90,43.80±7.28 mSv, respectively; Age attribution between two groups is significant difference (t=-3.58, p<0.01), is 65.6±10.4 and 60.8±8.1, respectively. BMI is 21.84±2.99 and 22.34±3.25 kg/m2, respectively (t=1.08, p>0.05). Compared to CA, the peripheral T lymphocyte count, CD4+T and CD8+T numbers are higher in HBRA, there is no statistic significance. Multivariable linear regression analysis indicants that T lymphocyte count, CD4+T and CD8+T lymphocyte numbers increased with cumulate dose, and CD8+T lymphocyte numbers increased significantly,b=0.001,p=0.036. CD8+T lymphocyte numbers increased 1% per 10 mSv.The cytokines profile expressed in HBRA and CA residents indicates, of 30 selected targets, 22 indexes were measurable and inflammatory cytokines such as IFN-γ, IL-α, MCP-1, IL-8, GRO, IL-10, VEGF, EGFR, sIL-6R and CRP levels were significant up regulated, Ratio>1.5 and q-values<0.05. After adjustment to age and BMI, these ten indexes increased significantly with cumulate dose, p<0.001.ELISA results verified the levels of IL-1α, IFN-γ, MCP-1 and sIL-6R, EGFR, CRP on cytokine profiles. The results show that the absolute levels of IL-la are lower than the . minimum detection. Other four indexes levels are consistent with cytokine expression in array profiles, and levels of IFN-y, MCP-1 and SIL-6R, EGFR, CRP in HBRA are significantly higher than in CA. Also, cumulate dose has the significant influence on the whole levels of five indexes expression. CRP, MCP-1, sIL-6R levels are linear with cumulate dose, log(CRP), log(MCP-1) and sIL-6R levels increased 8.68%,1.89%,84.51%per 10mSv, respectively. Also, the proportion of total variance (η2) of CRP, MCP-1, and sIL-6R that is attributed to dose is 0.21,0.15,0.26, respectively; but the linear relationship of IFN-y and EGFR are not well.3. Telomere length in HBRA (2.03±0.20) is significantly lower than control area (2.75±0.22), t=2.146, p=O.O35. With adjustment to age and BMI, telomere length in 50-,100-,200+mSv group is 0.520,0.558,0.569, respectively. Telomere length in HBRA increased 7.33% per 10 mSv.ConclusionImmune function was influnced, particularly the increase of CD8+T lymphocytes numbers in human exposed to long-term low dose radiation, and inflammatory biomarkers such as sIL-6R, CRP, MCP-1, IFN-y up regulate. Besides, long-term exposure to low dose radiation may affect the telomere length.