Stress results in an immune system that can't properly protect us, Australian research shows.
It isn't news that stress weakens the immune system, with many people believing they become sick after a particularly stressful period. And over the years, science has backed them up. Early animal studies linked stress and infection and research among US medical students late last century found their immunity fell during a stressful three-day exam period and their infection-fighting T-cells responded weakly to test-tube stimulation.
Since then, evidence has been mounting that bouts of stress result in an immune system that can't properly protect us – at least temporarily. Now, for the first time, scientists have been able to look inside the body to see why, says Scott Mueller, an immunology researcher with the University of Melbourne.
He is interested in the way the immune and nervous systems talk to each other. "There's good evidence that they're linked, but what's happening at a cellular level has been really difficult to chase down," he says.
To track cells in real time, he and his team used an advanced imaging technique called intravital microscopy.
"This is just a fancy microscope with a number of lasers on it that means we can shine deep into the tissue and see the cells as they're doing their job."
The study involved mice, some of which were given the neurotransmitter noradrenaline to simulate the stress of a massive shock – the equivalent of being attacked or receiving a cancer diagnosis. Other mice had been genetically engineered to switch on a stress response when given medication. And Mueller also used techniques such as applying thermal stress to the animals to produce a more natural pathway.
"The imaging showed us that stress caused immune cells to stop moving, preventing them from protecting against disease," he says.
"Movement is central to how immune cells get to the right parts of the body to mount a response against infections or tumours, so it was surprising to see that the stress signals had such a rapid and dramatic effect on how they move around. We had thought we might see a subtle effect, or we might have fewer immune cells coming into a tissue. We didn't expect that, from one minute to the next, they would just stop moving."
He worked mostly with T lymphocytes, cells that play a vital role in immunity to foreign substances. He also looked at other immune cells – macrophages, dendritic cells and B lymphocytes – and found all were affected, and that this could occur in many parts of the body.
In this instance, the paralysis was caused by sudden acute stress, but there is every reason to believe significant chronic stress may have the same effect.
It makes sense that in a crisis situation the body would dial down the immune system and focus its resources on pumping blood to the muscles and providing the energy required to escape a threat. But if ongoing high stress levels activate this same system over a longer period and keep immune cells from doing their work, it is going to have an effect.
Mueller's next focus is to look at how stress might affect the body's immune response to cancer and whether blocking signals from the nerves might benefit patients.
The immune system is enormously complex and he has supplied only a piece of the puzzle, but Mueller believes it is an important one, particularly as we cope with the threat of the Covid-19 pandemic.
"Most people know they need to manage their stress. This just gives you another reason to do that. It's more proof that it's not good to be overly stressed."
High stress levels may even dampen the efficacy of the Covid-19 vaccines.
"The types of immune challenges we tested in our study are very similar to a vaccine being delivered," says Mueller. "If you're overly stressed and your cells have stopped moving, it's quite likely that makes it harder [for the body] to mount a good response to the vaccine. So, get your vaccine and go and relax is probably the best advice."