The dreaded tick-borne encephalitis (TBE) virus infects various kinds of brain cells in several parts of the brain, depending on whether the affected person’s immune system is activated or not. That is shown in a recent study at Umeå University, Sweden.

“This increased understanding of how the virus behaves within the brain and the way it prompts the immune system is an important step in the event of effective treatments and preventive measures against this difficult disease,” says Anna överby, professor at Umeå University and leader of the research group behind the present study.

What the Umeå researchers have mapped is how the TBE virus infects the brain to cause encephalitis. The researchers developed a technique to three-dimensionally determine the placement of viruses within the brain of mice and determine which specific parts of the brain have been infected with TBE virus. The tactic relies on information from image analyses that were combined with studies of gene expression in several cell types. The result could be seen as a virus “road map” within the brain.

It turned out that there was an enormous difference between the spread of the virus within the brains of mice with and without an innate immune response. The virus infected different regions of the brain depending on the innate immune system of the mouse. When the researchers zoomed in on the cells within the infected brain regions, they might see that the immune system not only affected how the virus spread, it also modified which cell types were infected within the affected regions of the brain.

When the researchers zoomed in further, they might see that in cases where the immune system within the brain couldn’t be activated, the brain’s immune cells, microglia, were infected. Their task is otherwise to assist prevent and clear the infection. In mice that would activate their immune system within the brain, nevertheless, it was mainly nerve cells that were infected.

It’s already known that the innate immune system plays a crucial role in stopping the TBE virus from damaging the brain, but it surely has been unclear where and which cells they infect.

That is a crucial piece of the puzzle that’s now being put in place. The outcomes underline the importance of the immune system for those infected with TBE. We’ve got also opened up recent opportunities to review viruses that infect the brain with the brand new imaging methods we have now developed and by combining them with gene expression evaluation from individual cells.”

Anna överby, Professor at Umeå University

Tick-borne encephalitis virus, TBEV, just isn’t only a significant problem in Sweden, especially in tick-dense areas reminiscent of the Stockholm archipelago and within the Mälardalen region, but additionally an enormous problem in central and eastern Europe. The virus could cause serious brain inflammation with long-term disabilities in consequence. There may be currently no curative treatment for TBE, but an important measures are to stop infection by avoiding tick bites and to get vaccinated.

Source:

Journal reference:

Chotiwan, N., et al. (2023). Type I interferon shapes brain distribution and tropism of tick-borne flavivirus. Nature Communications. doi.org/10.1038/s41467-023-37698-0.