Read more: 鈥淚nfectious moods: How bugs control your mind鈥�
The decline in our memories in old age could be partly due to the ageing of immune cells, opening up new prospects for treatments
Could boosting the immune system keep your memory sharp as you age? Jonathan Kipnis of the University of Virginia in Charlottesville thinks so.
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Prompted by studies suggesting immune responses can help repair the nervous system, Kipnis and his colleagues created mice that lack CD4 cells, a kind of T-cell. They found the mice performed extremely poorly in tasks involving learning and memory, but when they were injected with CD4 cells from healthy mice, their memories improved (). Similarly, when he killed CD4 cells in healthy mice, their memory declined.
Further animal studies by Kipnis and others show that learning new tasks triggers a mild stress response within the brain, which prompts CD4 cells to rally to the meninges, the membranes that surround the brain. Here, they release IL-4, which both switches off the stress response and tells brain cells called astrocytes to release brain-derived neurotrophic factor, a protein that enhances learning ().
Whether these animal studies are relevant to human learning and memory remains unclear, but there is some indirect evidence to support it. For example, many chemotherapy drugs suppress the immune system, which might explain why some people with cancer develop 鈥渃hemobrain鈥� 鈥� a term used to describe the cognitive problems and memory loss associated with chemotherapy.
Sluggish immune cells might also explain why our brains slow down as we age. 鈥淭he number one cell affected by ageing is the T-cell,鈥� says Kipnis. 鈥淚鈥檓 not saying it鈥檚 the only factor leading to age-related dementia, but it could definitely be one of them.鈥�
If the immune system does play a role in human memory, this could lead to new classes of drugs to boost it. Kipnis is already developing such immune-based cognitive enhancers in mice, with the short-term goal of using them to treat Rett syndrome 鈥� a developmental disorder associated with behavioural problems that has recently been linked to abnormal T-cells.
Ultimately, Kipnis believes such drugs could be used not only to reverse age-related cognitive decline, but also to boost memory in healthy people. 鈥淚f you take a very smart human being you may not be able to make him smarter, but if you take someone who is just normal then you may be able to enhance memory,鈥� he says.
Others are reserving judgement for the moment. 鈥淚 think these experiments are very intriguing,鈥� says Bienenstock. It鈥檚 hard to believe that the immune system and the nervous system do not effect each other, he says, but the extent to which this happens is unclear. And even if Kipnis is right, the dangers of meddling with the immune system mean we need to know what we are doing before trying to boost people鈥檚 memory this way.
