Coming down with the flu can provoke relapses in multiple sclerosis (MS) patients by activating glial cells that surround and protect nerve cells. In a study in mice, scientists found that activated glial cells increase the levels of a chemical messenger in the brain that, in turn, triggers an immune reaction and, potentially, autoimmune attacks.
The study, “Influenza infection triggers disease in a genetic model of experimental autoimmune encephalomyelitis,” was published in the journal Proceedings of the National Academy of Sciences (PNAS).
The flu is caused by the human influenza virus and, despite being unpleasant, usually resolves itself within days. However, for people with MS and other neurological conditions, the flu can lead to disease relapse.
Researchers at the University of Illinois investigated what happens in the brain of MS patients during upper-respiratory viral infections, such as the flu.
“We know that when MS patients get upper respiratory infections, they’re at risk for relapse, but how that happens is not completely understood,” Andrew Steelman, an assistant professor at the university and the study’s senior author, said in a press release. “A huge question is what causes relapse, and why immune cells all of a sudden want to go to the brain. Why don’t they go to the toe?”
The team used a mouse model characterized by autoimmune responses within the brain and spinal cord — the type of deregulated immune responses seen in MS patients. Researchers infected the animals with a version of human influenza virus adapted to mice, and looked at changes that occurred in the animal’s central nervous system.
While the virus was never detected in the animals’ brains, upon infection some of the mice developed MS-like symptoms.
“If you look at a population of MS patients that have symptoms of upper respiratory disease, between 27 and 42 percent will relapse within the first week or two,” Steelman said. “That’s actually the same incidence and timeframe we saw in our infected mice, although we thought it would be much higher given that most of the immune cells in this mouse strain are capable of attacking the brain.”
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