Deep–space missions may alter immune cell phenotype in the primary (e.g., thymus) and secondary (e.g., spleen) lymphoid organsࣧcontributing to the progression of a variety of diseases. In deep space missions, astronauts will be exposed to chronic low doses of HZE radiation while being in microgravity. Ground-based models of long-term uninterrupted exposures to HZE radiation are not yet available. To obtain insight in the effects of concurrent exposure to microgravity and chronic irradiation (CIR), mice received a cumulative dose of chronic 0.5 Gy gamma rays over one month ± simulated microgravity (SMG). To obtain insight in a dose rate effect, additional mice were exposed to single acute irradiation (AIR) at 0.5 Gy gamma rays. We measured changes in proportions of immune cells relative to total number of live cells in the thymus and spleen, alterations in stress level markers in plasma, and change in body weight, food consumption, and water intake. CIR affected thymic CD3+/CD335+ natural killer T (NK-T) cells, CD25+ regulatory T (Treg) cells, CD27+/CD335- natural killer (NK1) cells and CD11c+/CD11b- dendritic cells (DCs) differently in mice subjected to SMG than in mice with normal loading. No such effects of CIR on SMG as compared to normal loading were observed in cell types from the spleen. Differences between CIR and AIR groups (both under normal loading) were found in thymic Treg and DCs. Food consumption, water intake, and body weight were less after coexposure than singular or no exposure. Compared to sham, all treatment groups exhibited elevated plasma levels of the stress marker catecholamine. These data suggest that microgravity and chronic irradiation may interact with each other to alter immune cell phenotypes in an organ–specific manner and appropriate strategies are required to reduce the health risk of crewmembers.

深空任务可能会改变初级（例如胸腺）和次级（例如脾脏）淋巴器官的免疫细胞表型，从而导致多种疾病的进展。在深空任务中，宇航员将在微重力环境中暴露于长期低剂量的 HZE 辐射。长期不间断地暴露于 HZE 辐射的地面模型尚不可用。为了深入了解同时暴露于微重力和慢性辐射 (CIR) 的影响，小鼠在一个月内接受了累积剂量的慢性 0.5 Gy 伽马射线 ± 模拟微重力 (SMG)。为了深入了解剂量率效应，将额外的小鼠暴露于 0.5 Gy 伽马射线的单次急性辐射 (AIR)。我们测量了免疫细胞相对于胸腺和脾脏中活细胞总数的比例变化，血浆中压力水平标志物的变化，以及体重、食物消耗和水摄入量的变化。CIR 在接受 SMG 的小鼠中对胸腺 CD3+/CD335+ 自然杀伤 T (NK-T) 细胞、CD25+ 调节性 T (Treg) 细胞、CD27+/CD335- 自然杀伤 (NK1) 细胞和 CD11c+/CD11b- 树突状细胞 (DC) 的影响不同与正常负荷的小鼠相比。与正常负荷相比，在脾脏的细胞类型中没有观察到 CIR 对 SMG 的这种影响。在胸腺 Treg 和 DC 中发现 CIR 和 AIR 组（均在正常负荷下）之间的差异。与单独接触或不接触相比，共同接触后的食物消耗、饮水量和体重减少。与假手术相比，所有治疗组都表现出应激标记儿茶酚胺的血浆水平升高。