Study: Extended gravity-free stay leads to decrease in immune cells

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A team of scientists at the Riken research institute has found a link between extended stays in a weightless condition and a decrease in immune cell production, which could impact astronauts’ health on long-term spaceflights.

However, the researchers believe the impact could be mitigated by exposure to artificial gravity during the space missions.

The team, led by Taishin Akiyama of the Laboratory for Immune Homeostasis under the Riken Center for Integrative Medical Sciences, compared the size of the thymus organ between mice on Earth and those at the International Space Station that were placed in a state of weightlessness for about a month.

The thymus produces cells that play a key role in maintaining immune systems.

Past research has found that the number of immune cells in astronauts who spend time in space decreases. The latest research could help unravel the process by which that occurs.

The group raised six mice in the Kibo research module on the ISS and examined them after they were brought back to Earth. Comparing the ratio of the weight of the thymus to the whole mice found that the mice in space had about a 60 percent decrease in the ratio in comparison to murine left on Earth. Moreover, the structure of the thymus among those mice that went into space had also altered, leading to a weakening in the functioning of the genes that play a role in multiplying immune cells.

The group also placed six mice on the ISS in equipment that allowed for the same level of gravity as on Earth. Those murine had a lower rate of decrease in the weight of the thymus.

The results of the research were published on Dec. 27 in the British scientific journal Scientific Reports.

Japan is one of the nations involved in a plan to have astronauts eventually live on the moon in a sustainable manner.

Akiyama said his group would continue research to learn how much artificial gravity would have to be applied for astronauts in space to minimize the effects on the thymus.

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