Immunological Risks of Spaceflight Could Compromise Mars Missions

Imagine being trapped in space with an enemy that grows stronger as you grow weaker. That's what astronauts on a long trip to Mars will have to face, concludes a report published in the November 2009 issue of the Journal of Leukocyte Biology. The authors found that spaceflight weakens the immune system while strengthening harmful microbes, increasing risk of serious infection and potentially preventing long-term manned missions.

Researchers reviewed studies exploring the effects of spaceflight conditions on microbes and immune systems in humans and animals. Their review suggests that spaceflight affects the development, quantity, and function of important immune cells. The authors found that low-gravity environments led to the suppression of T lymphocytes, which are important for the destruction of infected cells and the activation of other immune cells. The precise molecular mechanisms of this suppression are currently being investigated. In addition, the authors found that long-term spaceflight led to changes in the expression of antibodies: molecules that circulate in the blood and label invaders, tagging them for destruction by immune cells. However, the high variability of the results of the studies reviewed suggests that more investigation is necessary to delineate the complete effects of spaceflight on the immune system.

"When people think of space travel, often the vast distances are what come to mind first," said Jean-Pol Frippiat, one of the report's co-authors from Nancy-University in France, "but even after we figure out a way to cover these distances in a reasonable amount of time, we still need to figure out how astronauts are going to overcome disease and sickness."

In addition, according to several studies described in the report, the growth, strength and antibiotic resistance of some common pathogens increases during spaceflight. A low-gravity environment can lead to increased production of E. coli toxins and can alter gene expression in Salmonella typhimurium, which, in turn, increases virulence. Furthermore, radiation, highly prevalent beyond Earth's orbit, increases the rate of DNA mutations and thus the rate at which microbes may develop resistance to antibiotics that would normally be sufficient to treat infections on Earth.

The authors presented several promising dietary additions that could prevent the weakening of astronauts' immune systems. In particular, antioxidants, found in many fruits and other foods, can protect against the effects of radiation. Nucleotide supplements and AHCC, a compound extracted from mushrooms, may protect and even enhance the immune system. And it has recently been shown that exercise increases antibody production. Though several solutions have been presented, the authors highlighted the need for further investigation before such long-term voyages as a mission to Mars can be undertaken.

The benefits of studying spaceflight-associated weakening of the immune system are not limited to space travel. Methods developed to protect against infection can also be used to treat Earth-bound patients with compromised immune systems. Such advances may also benefit the millions afflicted with diseases such as HIV/AIDS that attack or weaken the immune system.

Though a trip to Mars seems further out of reach for now, said Frippiat, his team's findings do not preclude the establishment of a lunar base in preparation for future long-term interplanetary missions. The Moon is close enough for a quick return to Earth should the immune systems of astronauts stationed there be overwhelmed.

Author: Sarah Stanley

Reviewed by: Natasha Hochlowski and Yangguang Ou

Published by: Yangguang Ou

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