Abstract
Alterations of the immune system could seriously impair the ability to combat infections during future long-duration space missions. However, little is known about the effects of spaceflight on the B-cell compartment. Given the limited access to astronaut samples, we addressed this question using blood samples collected from 20 healthy male volunteers subjected to long-duration bed rest, an Earth-based analog of spaceflight. Hematopoietic progenitors, white blood cells, total lymphocytes and B-cells, four B-cell subsets, immunoglobulin isotypes, six cytokines involved in inflammation, cortisone and cortisol were quantified at five time points. Tibia microarchitecture was also studied. Moreover, we investigated the efficiency of antioxidant supplementation with a cocktail including polyphenols, omega 3, vitamin E and selenium. Our results show that circulating hematopoietic progenitors, white blood cells, total lymphocytes and B-cells, and B-cell subsets were not affected by bed rest. Cytokine quantification suggested a lower systemic inflammatory status, supported by an increase in serum cortisone, during bed rest. These data confirm the in vivo hormonal dysregulation of immunity observed in astronauts and show that bed rest does not alter B-cell homeostasis. This lack of an impact of long-term bed rest on B-cell homeostasis can, at least partially, be explained by limited bone remodeling. None of the evaluated parameters were affected by the administration of the antioxidant supplement. The non-effectiveness of the supplement may be because the diet provided to the non-supplemented and supplemented volunteers already contained sufficient antioxidants. Given the limitations of this model, further studies will be required to determine whether B-cell homeostasis is affected, especially during future deep-space exploration missions that will be of unprecedented durations.
Highlights
Bioastronautics programs have substantially expanded over the last 50 years
To address this question and given limitations in the availability and the experimental protocols that can be performed with samples from astronauts following space missions, we investigated B-cell homeostasis in healthy volunteers subjected to two months of head-down tilt bed rest, as this is the best and most integrated Earth-based analog of the microgravity of spaceflight [18]
We studied the effects of this trial at BDC-4, HDT20, HDT60 and R+13 on reticulocytes, erythrocytes and platelets as these cell types have been shown to be affected by bed rest [24–26], thereby indicating a modification of hematopoiesis which includes Blymphopoiesis
Summary
Bioastronautics programs have substantially expanded over the last 50 years. Medical and physiological findings from these missions have demonstrated that spaceflight negatively impacts numerous physiological systems. Space studies performed using the newt Pleurodeles waltl as an animal model showed that spaceflight affects antibody production in response to antigenic stimulation [4, 5] and that somatic hypermutations, which diversify antibody binding sites to improve their affinity, occur at a lower frequency in space following immunization [6]. Another study showed that two out of five cosmonauts involved in a long-term space mission onboard the International Space Station (ISS) presented significant changes in their IgM repertoire during the mission, that these modifications persisted up to 30 days after landing and likely affected the specificities of IgM binding sites [12] This last observation agrees with another study that demonstrated that the immune system of approximately half of astronauts who spent six months on the ISS is sensitive to spaceflight conditions [13]
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