Why You’re Stupid When You’re Sick
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A fascinating study by Jonathan Kipnis, a neuroimmunologist in the University of Virginia School of Medicine’s department of neuroscience, has shown that there really is a mind body connection when it comes to physical illness and mental acuity. Kipnis got the idea from his adviser, Michal Schwartz as he watched her studying how the brain repairs itself after an injury. From Disccover Magazine:
She [Schwarz] found that the brain depends on a type of immune cell known as the T cell, which normally kills infected cells or leads other immune cells in a campaign against foreign invaders. Her research suggested that T cells can also send signals that activate the brain’s resident immune cells, microglia and blood-borne macrophages, telling them to protect the injured neurons from toxins released by the injury.
Without T cells, Schwartz and other researchers have found, the brain does a bad job of healing itself. Kipnis was fascinated by the discovery because he knew that T cells cannot get past the blood-brain barrier. Yet apparently they could significantly influence the brain from a distance. He wondered if T cells did more for the brain than just help heal wounds. “The crazy idea came to me: What if we needed T cells for healthy brain function?” Kipnis says.
Kipnis then performed an experiment rearing two separate groups of genetically identical mice -one normal and another without T cells. Kipnis then sent the mice to a colleague, Hagit Cohen at Ben-Gurion University of the Negev, to see how well they could learn a new trick. What they found was extraordinary – the mice without T cells were completely stupid and couldn’t learn anything. To get more specific results, he then isolated the brain only from receiving T-cells:
It has long been known that the membranes encasing the brain, called the meninges, are loaded with T cells and other immune cells. Kipnis and his colleagues wondered how smart mice would be if they had a normal supply of T cells everywhere in their bodies except the meninges, so he injected a compound into mice that prevented T cells from reaching the meninges. When those animals were put into a water maze, they, too, performed badly—just as Kipnis had predicted.
The science behind it is as follows:
When we learn something new, our neurons tear down old connections and build new ones. In the process they cast off lots of molecules. To the immune system, this waste may look like an infection or some other kind of trouble, resulting in inflammation and the release of harsh compounds that normally fight viruses but can also interfere with the brain and its function.
Kipnis suggests that T cells keep this process in check, differentiating between disease and ordinary stress and, when warranted, telling other immune cells to stand down by releasing antagonist molecules that prevent misguided inflammation.
The same T cells that protect the brain from inflammation also work to keep us sharp; and in what appears to be a feedback loop, the mere act of learning reinforces the effect.
What can we learn from this? Firstly, it changes how future brain-immune medicine could work. In another experiment, scientists drew blood from old mice whose supply of T cells was depleted and isolated their immune cells. They then added IL-4 to the flasks where they reared those immune cells and injected the IL-4-exposed cells back into the mice. The old mice were then able to perform mental tasks at a higher level, leading Kipnis to believe that it could be a fantastic therapeutic tool for the elderly, who spend much of the time fighting off illnesses as they age. As Kipnis says “We can’t really get inside the brain and fix things. But we can take the immune system out of the body, we can put it back in, we can do almost anything we want to it.”
On a more practical level, it means taking sick days when you’re actually sick. Americans have a bizarre habit of never taking time off, even when they’re seriously ill. The science now shows that this is completely counterproductive. You simply won’t be able to perform while bunged up and coughing all over the place. From an evolutionary point of view, this make a lot of sense:
When we’re sick, Kipnis proposes, it’s more important to launch a powerful immune attack than to have a sharp mind. “Everything in life is priorities,” he says.
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