13 October 2005
Fighting Fit For Space Travel
by Kate Melville
The suppression of the human immune system in space was first observed forty years ago during the Apollo missions when more than half the astronauts reported a bacterial or viral infection either during or shortly after their mission. To further study the effects of micro-gravity on the immune system, a shuttle flight in 1991 carried out experiments that identified T-cells as the components of the immune system that were compromised. That experiment was carried out by San Francisco VA Medical Center researcher Millie Hughes-Fulford, who has now built on that knowledge by identifying the specific mechanism behind the compromised T-cells. Her new research is published in the journal FJ Express.
Hughes-Fulford and her co-researchers have identified a signaling pathway called PKA that in a gravity field responds to the presence of a pathogen by stimulating the expression of 99 genes that in turn cause the activation of T-cells, which are essential for proper immune function. The researchers found that in the simulated absence of gravity, the PKA pathway did not respond to the pathogen's presence; as a result, 91 genes were not induced and eight genes were significantly inhibited, severely reducing the activation of T-cells. There are only two known situations in which T-cell function is so severely compromised: HIV infection and weightlessness. Interestingly, the researchers found that three other pathways which regulate immune function - P13K, PKC, and pLAT - were not affected by a lack of gravity. The experiment was carried out on human immune cells in culture that were placed in a device called a random positioning machine, which simulates weightlessness.
"This is a specific signal pathway that is not working in the absence of gravity," said Hughes-Fulford. "You're short-circuiting a whole lot of the immune response - namely, the ability to proliferate T-cells - which shouldn't be a surprise, because life evolved in Earth's gravity field."
Hughes-Fulford speculates that cell structure may trigger the effect. "Why do some pathways work and some not? Perhaps it's differences in the cytoskeleton - the interior architecture of the cell. It's the infrastructure of the cell, a membrane made of lipid, and maybe without gravity it's not as well-organized as it should be."
The problem of immune function in space must be solved if human beings are ever to live in space for extended periods of time. Hughes-Fulford believes the new findings provide a potential key to developing treatments and she intends to further her studies when Russian cosmonauts carry a custom-designed container housing the same experiment aboard a Soyuz spacecraft. "We know how these genes behave in simulated microgravity," she said. "The results from Soyuz should tell us what happens during spaceflight, in real microgravity."
Source: University of California - San Francisco