Research brief: Immune system dynamics in microgravity
If you're working on a proposal for Genes in Space 2020, we know many of you are planning to focus your project on the immune system. Understanding and overcoming the immune system deficiencies faced by astronauts is a priority for NASA and other space agencies. But — aside from two past Genes in Space investigations — what is currently being done to explore the molecular changes that lead to these deficiencies?
We asked Dr. Randall Gregg, an immunologist based at Lincoln Memorial University, to share the latest in space immunology research. Writing with his daughter, 2019 Genes in Space Junior Scientist Award winner Karley Gregg, he shared the results of one of his recent investigations, which was published last year in the journal Scientific Reports. Dr. Gregg shares his findings below.
Guest post by researcher Dr. Randal Gregg and his daughter, Karley Gregg
What was the purpose of this study?
One of the most important problems to overcome in the next step of space exploration to Mars and worlds beyond is ensuring the health of the astronauts. Since the early days of the space program, we’ve known that astronauts experience a reduction in the immune response. Just seven days of spaceflight causes a decrease in the activity of T cells, one of the main players of the immune response. We don’t know where this decrease in activity comes from. One possibility is that dendritic cells (DC), which direct the action of T cells, are impaired in microgravity. We investigated that possibility here.
What exactly did you do?
We used a rotating cell culture system to create an environment like microgravity called simulated microgravity (SMG) in which to grow the cells. We grew DC in simulated microgravity for 3, 7, 12, and 14 days (we called these groups of cells SMG DC). For control, another group of DC were grown in normal conditions over the same time (called static DC). At the end of each growth point, the DC were put into a tube with T cells. The next day, the activity of the T cells was measured to see if T cells that had been incubated with DC grown in simulated microgravity were less active than T cells incubated with DC from normal conditions.
What did you find?
We were shocked to see that T cells appeared to behave differently based upon how long DC were exposed to simulated microgravity. When DC were grown in simulated microgravity for less than 7 days, the T cells were hyperactivated by the DC. Surprisingly, that hyperactivation turned into hypoactivation when growing the DC in simulated microgravity for more than 7 days. But when you look closely at the activity of T cells grown with SMG DC, the T cell response starts to get better the longer DC are left in microgravity.
Figures 4a and 5c from Tackett, et al. The figure shows activation of the immune system as measured by T cell release of the protein interleukin-2 (IL-2). Left: T cell activity increases (i.e., they release more IL-2) when activated by DC grown for 3 days in SMG. Right: T cell activity decreases when activated by DC grown in SMG for 7 to 14 days (compare SMG (black bar) to Static (gray bars) conditions).
What does this mean for the future of space exploration?
Our results suggest that spaceflight of one week or more has a negative impact upon our body’s ability to respond to microbes. During this time, astronauts could be at high risk for infections and even cancers from space radiation. However, immune function appeared to be improving from day 7 to day 14. We will next study the function of DC during long-duration SMG exposure. This information will help in the development of treatments to keep astronauts healthy until the immune system has adapted to microgravity and ensure safe exploration of the next worlds.
About the author
With astronaut health a major concern for long-duration space travel to and colonization of other worlds, Dr. Randal Gregg’s lab works on the effects of microgravity upon the functioning of the immune system. His aim is to understand the molecular events altered by microgravity in order to develop countermeasures to preserve immune function and astronaut well-being.
Inspired by this research? Have your own idea for a follow-up study? Submit it to Genes in Space! Application deadline: April 25, 2020.