Immunology in SPACE!

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On Saturday, this Tweet came across my feed and rather caught my attention.  The cell picture is what caught my attention first, closely followed by the text: T-cell in Microgravity.

My Ph.D. is in Biomedical Sciences, and I studied Immunology for my research.  In particular, I was looking at the immune system in the brain and how it responded to viral infections of the brain.  I found this concept immediately arresting because SPACE! I love space and I’ve always wanted to go into space and if NASA (or someone) offered me a chance of reaching Mars with a 50% chance at surviving on the surface I would go immediately.  But with regard to the immune system, this did not immediately make sense to me: why would anyone study the effects of microgravity on the immune system? How would anyone come up with such an idea?  Is it plausible to think that there might be some effects?

Even going back to the beginnings of the space program, we worried about astronaut health, but this was more due to the fact that medical care was… rather far away.  Your immune system is all you’ve got, and it’s pretty good at defending you.  But could microgravity (or zero-gravity) affect how well it functions? Perhaps.

I suppose the first thing to consider is that you’re stuck in a closed environment with other people.  Germs quickly become community property and are likely pretty universal, but what if someone has a latent viral infection (like, say, chicken pox) and someone else isn’t immune?  What if some freaky-weird space virus gets on the space suits and infects the crew?  These aren’t particularly plausible concerns (especially the second), but you do have to postulate that somehow, some new pathogen might get into the environment.  Maybe your experiment escapes and you have to worry about a mutant rampant fungus.  I don’t know.  But let’s assume that this pathogen gets into the body somehow.  What then?

The immune system has several sort of generic sets of cells that patrol for invaders.  If and when you get an infection, these cells are supposed to migrate toward the lymph node that serves that tissue.  For example, if you eat the pathogen, these immune cells should probably hit your cervical (neck) lymph nodes.  Except that fluid travel on Earth is used to having GRAVITY.  So, could microgravity disrupt that?  Possibly.

Once these first-defense immune cells arrive in the lymph nodes, their job is to activate T cells.  Physical contact is required for this, and there are lots of molecules involved in holding the immune cells together for a brief period to activate them.  That junction/border between the T cell and its activator is called the immunological synapse. Could that be affected by microgravity?  Again, maybe.  I’m not certain this is plausible because I imagine those interactions sort of like Velcro, and I’m not sure that they’re going to be gravity-dependent.

The T cells are then supposed to replicate and differentiate.  Gravity-dependent? Harder to say.  We do know that microgravity conditions affect bone and muscle cell growth and differentiation 1-3.  That makes sense because our bones and muscles on Earth are pretty gravity-dependent; weight-bearing exercise increases both muscle mass and bone density.  Perhaps more surprisingly, though, additional research shows that microgravity also affects male reproductive cells (in mice) 4 and even how sensitive cancer cells are to chemotherapy 5.  These studies lend some credence to the idea that immune system function might be affected by microgravity!

Once the T cells are activated, they’re supposed to migrate back to the site of infection following a chemical trail left by the first defense cells.  That may or may not be gravity-dependent as well.  Then, on arrival, they must physically interact with and identify infected cells: more Velcro.  Finally, they have to kill the infected cells.  Along the way, some of these T cells are converted (differentiate) into memory cells, in case your body sees that same pathogen again.

Now, here’s what the Principal Investigator (PI) has to say about her work:

I think this research is tremendously exciting and I wish I were in that lab and participating!  It can be hard to justify and explain why these types of studies are important.  I’m probably never going into space.  I doubt many of you who read this (or your children) are, either. But what if? As we explore and learn more and take our first tentative steps into that out there, being informed is good.  And what if, just what if, we learn from such experiments that T cells grown in microgravity can aggressively attack and kill cancer cells? What value might that have?  I am so excited about this payload and I can’t wait to read the results (which will be a while. Science requires patience.)

 References

  1. PLoS One. 2013 Oct 7;8(10):e76710. doi: 10.1371/journal.pone.0076710. eCollection 2013.
  2. Cell Cycle. 2013 Sep 15;12(18):3001-12. doi: 10.4161/cc.26029. Epub 2013 Aug 14.
  3. Aviakosm Ekolog Med. 2012 Sep-Oct;46(5):64-7. Russian.
  4. PLoS One. 2010 Feb 4;5(2):e9064. doi: 10.1371/journal.pone.0009064.
  5. Neurosci Lett. 2009 Sep 29;463(1):54-9. doi: 10.1016/j.neulet.2009.07.045. Epub 2009 Jul 21.

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