[en] The goal was to investigate the T helper (Th) response in splenocytes of mice exposed to low-dose/low-dose-rate (LDR) γ-rays, simulated solar particle event protons (sSPE), or combination of both. C57BL/6 mice were exposed to LDR γ-radiation (⁵⁷Co) to a total dose of 0.05 Gray (Gy) at 0.024 cGy/h, either with or without subsequent exposure to 2 Gy sSPE protons. Expression of genes related to Th cells was evaluated immediately after exposure (day 0). On day 21, intra- and extracellular cytokine production was assessed after activation with anti-CD3 monoclonal antibodies (mAb) or phorbol 12-myristate 13-acetate/ionophore (PMA/I). Five genes were significantly modulated on day 0 in one or more of the irradiated groups compared to controls (p<0.05): Ccl11, Ccr5, Cd80, Inha, and Il9. On day 21, numbers of cells positive for interferon-γ were high in the LDR + sSPE group versus 0 Gy and LDR γ-rays (p<0.05), but there was no difference in interleukin (IL)-2 and tumor necrosis factor (TNF)-α. Levels of secreted cytokines after anti-CD3 mAb activation were high for 5 (maximum intensity projection (MIP)-1α, GM-CSF, interferon (IFN)-γ, TNF-α, IL-13) and low for 2 (IL-7, IL-9) in all irradiated groups. Priming with LDR photons had a significant effect on IFN-γ and IL-17 compared to sSPE protons alone; IL-2 was low only in the LDR + sSPE group. The cytokine patterns after anti-phorbol myristate acetate (PMA)/ionomycin (I) activation were different compared to anti-CD3 mAb and with fewer differences among groups. The data show that total-body exposure to space-relevant radiation has profound effects on Th cell status and that priming with LDR γ-rays can in some cases modulate the response to sSPE. (author)

[en] A better understanding of low dose radiation effects is needed to accurately estimate health risks. In this study, C57BL/6 mice were γ-irradiated to total doses of 0, 0.01, 0.05, and 0.1 Gy (⁵⁷Co; -0.02 cGy/h). Subsets per group were euthanized at the end of irradiation (day 0) and on days 4 and 21 thereafter. Relative spleen mass and splenic white blood cell (WBC) counts, major leukocyte populations, and spontaneous DNA synthesis were consistently higher in the irradiated groups on day 0 compared to 0 Gy controls, although significance was not always obtained. In the spleen, all three major leukocyte types were significantly elevated on day 0 (P<0.05). By day 21 post-irradiation the T, B, and natural killer (NK) cell counts, as well as CD4⁺ T cells and CD4:CD8 T cell ratio, were low especially in the 0.01 Gy group. Although blood analyses showed no significant differences in leukocyte counts or red blood cell and platelet characteristics, the total T cells, CD4⁺ T cells, and NK cells were increased by day 21 after 0.01 Gy (P<0.05). Gene analysis of CD4⁺ T cells negatively isolated from spleens on day 0 after 0.1 Gy showed significantly enhanced expression of Il27 and Tcfcp2, whereas Inha and Socs5 were down-regulated by 0.01 Gy and 0.1 Gy, respectively (P<0.05). A trend for enhancement was noted in two additional genes (Il1r1 and Tbx21) in the 0.1 Gy group (P<0.1). The data show that protracted low dose photons had dose- and time-dependent effects on CD4⁺ T cells after whole-body exposure. (author)

[en] The probability that a dose of ionizing radiation kills a cell is about 10,000 times the probability that the cell will be transformed to malignancy. On the other hand, the number of cells killed required to significantly impact health is about 10,000 times the number that must be transformed to cause a late malignancy. If these two risks, cell killing and malignant transformation, are about equal, then the risk that occurs during a mission is more significant than the risk that occurs after a mission. The latent period for acute irradiation effects (cell killing) is about 2-4 weeks; the latent period for malignancy is 10-20 years. If these statements are approximately true, then the impact of cell killing on health in the low-gravity environment of space flight should be examined to establish an estimate of risk. The objective of this study is to synthesize data and conclusions from three areas of space biology and environmental health to arrive at rational risk assessment for radiations received by spacecraft crews: (1) the increased physiological demands of the space flight environment; (2) the effects of the space flight environment on physiological systems; and (3) the effects of radiation on physiological systems. One physiological system has been chosen: the immune response and its components, consisting of myeloid and lymphoid proliferative cell compartments. Best-case and worst-case scenarios are considered. In the worst case, a doubling of immune-function demand, accompanied by a halving of immune capacity, would reduce the endangering dose to a crew member to around 1 Gy

[en] Purpose: Exposure to various forms of radiation, including iron ions that have an exceptionally high biological effectiveness, is an inevitable consequence of spaceflight. However, genetic background can significantly influence the response to radiation and hence also the overall health of crewmembers. The major goal of this study was to compare leukocyte population responses in two strains of mice that differ in susceptibility to radiation: C57BL/6 (resistant) and CBA/Ca (susceptible). Materials and methods: The mice were whole-body irradiated with 0, 50, 200, or 300 cGy ⁵⁶Fe²⁶ (1 GeV) at ∼1 Gy/min and euthanised on days 4 and 30 thereafter for analyses. Analyses included body and organ masses (spleen, liver, thymus, lungs), distribution of leukocyte populations in blood and spleen, red blood cell and platelet characteristics, expression of surface molecules (CD11b, CD54), and spontaneous and mitogen-induced blastogenesis. Results: There were main effects of Dose and Dose × Day interactions on virtually all quantified parameters in both strains of mice. In contrast, there were relatively few Dose × Strain and three-way interactions. Strain-related interactions involved changes in circulating phagocytic populations, erythrocytes, and liver mass. Conclusion: The data demonstrate that genetic background can modify certain immune-related parameters after exposure to heavy particle radiation. The possible implications of these findings are discussed. (authors)

[en] Purpose: Particle radiations could significantly impact astronaut health during space missions. This study quantified the effects of iron ion radiation on lymphocytes in two strains of mice differing in susceptibility to radiation-induced acute myeloid leukemia (AML) and thymic lymphoma (TL): C57BL/6 (AML resistant, TL sensitive) and CBA/Ca (AML sensitive, TL resistant). Materials and methods: The animals (n = 60/strain) were irradiated with ⁵⁶Fe²⁶⁺ (1 GeV) to total doses of 0, 0.5, 2 and 3 Gray (Gy) at an average dose rate of 1 Gy/min and euthanised on days 4 and 30 thereafter; blood, spleen, and bone marrow were collected for flow cytometry analyses. Cells expressing the following molecules were quantified: Cluster of differentiation (CD) 4, CD8, CD25, CD34, CD71, B220 (isoform of CD45 on B cells), NK1.1 (marker on natural killer or NK cells, C57B mice), panNK (marker on NK cells, CBA mice), and Sca1 (stem cell antigen 1). Results: Exposure to radiation resulted in different distribution patterns in lymphocyte populations and leukocytes expressing activation and progenitor markers in the two mouse strains. Significant main effects were dependent upon strain, as well as radiation dose, body compartment, and time of assessment. Especially striking differences were noted on day 4 after 3 Gy irradiation, including in the CD4:CD8 ratio [blood, C57 (2.83 ± 0.25) vs. CBA (6.19 ± 0.24); spleen, C57 (2.29 ± 0.12) vs. CBA (4.98 ± 0.22)], %CD25⁺ mononuclear cells in bone marrow [C57 (5.62 ± 1.19) vs. CBA (12.45 ± 0.93)] and %CD34”+Sca1”+ cells in bone marrow [CD45l° gate, C57 (2.72 ± 0.74) vs. CBA (21.44 ± 0.73)]. Conclusion: The results show that genetic background, as well as radiation dose and time post-exposure, had a profound impact on lymphocyte populations, as well as other leukocytes, after exposure to iron ion radiation. (authors)

[en] Purpose: Astronauts on missions are exposed to low-dose/low-dose-rate (LDR) radiation and could receive high doses during solar particle events (SPE). This study investigated T cell function in response to LDR radiation and simulated SPE (sSPE) protons, alone and in combination. Materials and methods: C57BL/6 mice received LDR γ-radiation (⁵⁷Co) to a total dose of 0.01 Gray (Gy) at 0.179 mGy/h, either with or without subsequent exposure to 1.7 Gy sSPE protons delivered over 36 h. Mice were euthanised on days 4 and 21 post-exposure. T cells with cluster of differentiation 4 (CD4⁺) were negatively isolated from spleens and activated with anti-CD3 antibody. Cells and supernatants were evaluated for survival/signalling proteins and cytokines. Results: The most striking effects were noted on day 21. In the survival pathway, nuclear factor-kappaB (NF-κB; total and active forms) and p38 mitogen activated protein kinase (p38MAPK; total) were significantly increased and cJun N-terminal kinase (JNK; total and active) was decreased when mice were primed with LDR γ-rays prior to sSPE exposure (P < 0.001). Evaluation of the T cell antigen receptor (TCR) signalling pathway revealed that LDR γ-ray exposure normalised the high sSPE proton-induced level of lymphocyte specific protein tyrosine kinase (Lck; total and active) on day 21 (P < 0.001 for sSPE vs. LDR + sSPE), while radiation had no effect on active zeta-chain-associated protein kinase 70 (Zap-70). There was increased production of interleukin-2 (IL-2) and IL-4 and decreased transforming growth factor-β1 in the LDR + sSPE group compared to the sSPE group. Conclusion: The data demonstrate, for the first time, that protracted exposure to LDR γ-rays can significantly modify the effects of sSPE protons on critical survival/signalling proteins and immunomodulatory cytokines produced by CD4⁺ T cells. (authors)

[en] Purpose: To determine whether differences exist between proton and electron radiations on biological responses after total-body exposure. Materials and methods: ICR mice (n = 45) were irradiated to 2 Gray (Gy) using fully modulated 70 MeV protons (0.5 Gy/min) and 21 MeV electrons (3 Gy/min). At 36 h post-irradiation liver gene expression, white blood cell (WBC), natural killer (NK) cell and other analyses were performed. Results: Oxidative stress-related gene expression patterns were strikingly different for irradiated groups compared to 0 Gy (P < 0.05). Proton radiation up-regulated 15 genes (Ctsb, Dnm2, Gpx5, Il19, Il22, Kif9, Lpo, Nox4, Park7, Prdx4, Prdx6, Rag2, Sod3, Srxn1, Xpa) and down-regulated 2 genes (Apoe, Prdx1). After electron irradiation, 20 genes were up-regulated (Aass, Ctsb, Dnm2, Gpx1, Gpx4, Gpx5, Gpx6, Gstk1, Il22, Kif9, Lpo, Nox4, Park7, Prdx3, Prdx4, Prdx5, Rag2, Sod1, Txnrd3, Xpa) and 1 was down-regulated (Mpp4). Of the modified genes, only 11 were common to both forms of radiation. Comparison between the two irradiated groups showed that electrons significantly up-regulated three genes (Gstk1, Prdx3, Scd1). Numbers of WBC and major leukocyte types were low in the irradiated groups (P < 0.001 vs. 0 Gy). Hemoglobin and platelet counts were low in the electron-irradiated group (P < 0.05 vs. 0 Gy). However, spleens from electron-irradiated mice had higher WBC and lymphocyte counts, as well as enhanced NK cell cytotoxicity, compared to animals exposed to protons (P < 0.05). There were no differences between the two irradiated groups in body mass, organ masses, and other assessed parameters, although some differences were noted compared to 0 Gy. Conclusion: Collectively, the data demonstrate that at least some biological effects induced by electrons may not be directly extrapolated to protons. (authors)

[en] A radiation biology experiment was performed in the research room of the proton therapy facility at Loma Linda University Medical Center to simulate the proton exposure produced by a solar particle event. The experiment used two scanning magnets for X and Y deflection of the proton beam and covered a usable target area of nearly 1 m². The magnet scanning control system consisted of Lab View 6.0 software running on a PC. The goal of this experiment was to study the immune system response of 48 mice simultaneously exposed to 2 Gy of protons that simulated the dose rate and energy spectrum of the September 1989 solar particle event. The 2 Gy dose was delivered to the entrance of the mice cages over 36 h. Both ion chamber and TLD measurements indicated that the dose delivered was within 9% of the intended value. A spot scanning technique using one spot per accelerator cycle (2.2 s) was used to deliver doses as low as 1 μGy per beam spot. Rapid beam termination (less than 5 ms) on each spot was obtained by energizing a quadrupole in the proton synchrotron once the dose limit was reached for each spot. A parallel plate ion chamber placed adjacent to the mice cages provided fluence (or dose) measurements for each beam energy during each hour of the experiment. An intensity modulated spot scanning technique can be used in a variety of ways for radiation biology and a second experiment is being designed with this proton beam scanning system to simultaneously irradiate four groups of mice with different dose rates within the 1 m² area. Also, large electronic devices being tested for radiation damage have been exposed in this beam without the use of patch fields. The same scanning system has potential application for intensity modulated proton therapy (IMPT) as well. This paper discusses the beam delivery system and dosimetry of the irradiation