Why infections like flu exacerbate symptoms of neurological diseases
In most cases, the symptoms of the flu only last a relatively short period of time. However, for people with neurological diseases like multiple sclerosis (MS), the flu can significantly exacerbate symptoms of their disease and increase the risk for relapse. Why this occurs remains largely unknown.
Researchers from the University of Illinois Urbana–Champaign have gained important insights into this question. Their study, titled "Influenza infection triggers disease in a genetic model of experimental autoimmune encephalomyelitis," is published in the Proceedings of the National Academy of Sciences.
Andrew Steelman, the principle investigator of the study, and colleagues started with transgenic mice that are susceptible to autoimmune brain damage. They exposed the mice to influenza A virus and investigated how it changed the animals' behavior and brain. Results showed that some of the infected mice exhibited MS-like symptoms.
Next, the team used wild-type mice to demonstrate that infection altered the transcriptome of the cerebellum and spinal cord. Consistently, glia cells appeared to be activated, and immune cells including T-cells, monocytes and neutrophils were increased in the brain several days after infection.
Glia cells, a main type of cells in the nervous system, are best known for their role in providing support for neurons. This study indicates that glia cells may have additional functions. Specifically, some glia cells may play a role in recruiting immune cells like T-cells, monocytes and neutrophils to the brain, the study suggests.
Furthermore, the researchers discovered that a protein called CXCL5 was increased the brains of flu-infected mice and in cerebrospinal fluid of MS patients during relapse. Besides, a separate study has identified CXCL5 as a possible predictor of relapse.
Taken together, the new study extends our understanding of why infections like flu can exacerbate symptoms of neurological diseases like MS. Moreover, CXCL5 might be involved in infection-induced relapse in MS patients, but this hypothesis requires further research.