Viruses often spread through the brain in patchwork patterns, infecting some cells but missing others. New research at Washington University School of Medicine in St. Louis helps explain why. The scientists showed that natural immune defenses that resist viral infection are turned on in some brain cells but switched off in others.
"The cells that a pathogen infects can be a major determinant of the seriousness of brain infections," says senior author Michael Diamond, MD, PhD, professor of medicine. "To understand the basis of disease, it is important to understand which brain regions are more susceptible and why."
While some brain infections are caused by bacteria, fungi or parasites, often the cause is a virus, such as West Nile virus, herpesvirus or enteroviruses.
For their study, now available online in Nature Medicine, the researchers focused on granule cell neurons, a cell type that rarely becomes infected. They compared gene profiles in granule cells from the cerebellum with the activity in cortical neurons in the cerebral cortex, which are more vulnerable to infection.
The comparison revealed many differences, including a number of genes in cortical neurons that were less well-expressed—meaning that for those specific genes there were fewer copies of mRNA, the molecules that relay genetic information from DNA to the cell's protein-making mechanisms.