Scientists in Wales may have cracked open a new way to think about Alzheimer's disease — and it starts with the virus that gives you cold sores.
A team at Cardiff University's School of Medicine has shown how herpesvirus infections can trigger the immune system to speed up dementia in mice. The research, published in the journal Brain, found that when herpesvirus infected mice bred to develop Alzheimer's, the virus caused a flood of immune cells called CD8+ T cells to pour into the brain. These cells, meant to fight infection, appeared to accelerate the damage that leads to memory loss and cognitive decline.
"Infections, including chronic human herpesviruses which can be associated with cold sores, have long been suspected as increasing the risk of developing Alzheimer's disease," said Dr. Mathew Clement, one of the researchers. "However, the mechanisms underlying this association have remained largely unknown."
To study this, the researchers used mice that carry genes linked to Alzheimer's disease, called 3xTg-AD mice. They infected some mice with a herpesvirus and then tested their memory and brain health. They also gave some mice an antiviral drug called valganciclovir hydrochloride, while others received treatments that removed certain white blood cells.
The results were striking. Mice that received antivirals or had their immune cells reduced performed better on memory tests — a key measure of how well the brain is working. This suggests that controlling the immune response to herpesviruses might actually slow down dementia.
The findings build on earlier research that spotted the same type of T cells in the brains and spinal fluid of human Alzheimer's patients. Professor Ian Humphreys, who co-led the study, urged caution about overinterpreting the results. "It remains unclear how virus-induced T cell presence in the brain leads to disease progression," he said. "These results should be viewed as one piece of a much larger puzzle rather than proof that herpesviruses cause Alzheimer's disease."
Still, the researchers say the work points to a future where preventing infections through vaccines and antiviral treatments might also help prevent or delay dementia. As Dr. Clement put it, "dementia risk is not as simple as genetic predisposition, but that environmental factors play an important part."
For the 55 million people worldwide living with dementia, this research offers not a cure, but a clue — and maybe, eventually, a new way to fight back.