Background: There is epidemiological evidence that suggests there are beneficial effects of ionizing radiation at low doses. Some experimental studies confirmed this hormetic effect with doses of about 1 cGy/day, but no data concerning very low dose rates are available. Objective: The aim of this study was to determine the life span of mice exposed to very low doses of ionizing radiation. Methods: Six hundred female C57BL/6 mice, 1 month old, were exposed to chronic gamma irradiation at very low dose rates of 7 or 14 cGy/year. These doses are about 25 or 50 times higher than background, but much lower than the doses of about 1 cGy/day used in previous experiments. Three hundred mice living in the same room were used as controls. Results: The life span, after the beginning of the experiment, determined by the survival time of 50% of each population, is increased in irradiated mice: 549 days in controls, 673 days in both irradiated groups. The differences are significant between the control and the irradiation mice. Differences between mice irradiated with 7 or 14 cGy are not significant. Conclusions: These results confirm the possibility of a nonharmful effect (hormesis) of ionizing radiation. They demonstrate that the paradigm, which states that low-dose effects can be predicted high-dose effects, cannot be systematically applied in radiation biology in general and gerontology in particular.

Limited data exist on the cytokine and cellular changes in the alveolar environment in immunocompromised patients during Pneumocystis jirovecii infection. A cellular and a cytokine analysis were performed on bronchoalveolar lavage (BAL) samples from three groups of patients, i.e., an initial study group of 64 immunocompromised P. jirovecii-positive individuals and two control groups of P. jirovecii-negative patients who had been or not immunosuppressed (65 patients). The results were related to alveolar dilution as determined by urea measurement. Compared with non-infected groups, P. jirovecii-infected patients had a lower level of alveolar macrophages (AM), particularly those with high burdens of P. jirovecii. Alveolar macrophages over-expressed the Dectin-1 receptor, which was largely implicated in P. jirovecii clearance. The alveolar CD8+T and CD4+T lymphocyte counts were increased and an inverse correlation was observed between the alveolar CD4+ cell count and the P. jirovecii burden. Although the alveolar IL-6 level was considerably increased, alveolar IL-17, IL-10, TNF-α, TGF-β concentrations of P. jirovecii patients were not different from the control groups. Changes in the pulmonary environment were also highlighted during P. jirovecii colonization. Our study suggests that there is a correlation between the P. jirovecii burden in the alveolus (from colonization to a high P. jirovecii burden), and the degree of impairment of the alveolar immune response.

Forty-one cases of histiocytic sarcoma (HS) in C57BL/6J mice were histopathologically studied with special regard to unexpected associated hematopoietic disorders. These cases were retrieved among C57BL/6J female mice used as control mice in a chronic low-dose irradiation experiment. Hematopoietic characteristics were analysed by comparison to 41 disease-free mice from the same cohort. Tumoral involvement of the liver was observed in all 41 HS-bearing mice, followed by infiltration of the spleen (61.8%), lung (32.4%), bone marrow (14.3%), uterus (12.2%), lymph node (9.8%), and kidney (2.4%). By comparative analysis, we were able to demonstrate a significant association of HS with liver hematopoiesis (89.5% in HS group vs 15% in control mice, p < 0.00001), and with central hematopoietic disorders involving the myelocytic cells (decreased in HS, p = 0.003) and erythrocytic cells (increased in HS, p = 0.001). Microscopic characteristics of these 41 cases and physiopathology of the newly described hematopoietic features in HS are further discussed.

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