GoKawiilSome immune cells make the long journey from the gut to membranes surrounding the brain. Credit: Steve Gschmeissner/SPL/Alamy
Immune cells that fight stomach bugs can migrate from the gut to the brain, where they establish a lasting ‘memory’ of previous infection, according to a study in mice.
The brain is shielded by protective membranes called meninges, which guard the central nervous system against pathogens circulating in the blood. When mice in the study were infected with common bacteria and parasites that cause intestinal illness, immune cells journeyed from the gut to the meninges. Once there, the cells became residents that responded to a second round of infection more than a month after the first, suggesting that they kept a record of past illnesses.
The study is “outstanding” and could help researchers to learn more about how the gut interacts with the central nervous system, says Francisco Quintana, a neuroimmunologist at Harvard University in Cambridge, Massachusetts. “It opens up several possibilities,” he says, such as exploring how gut infections might affect neurological disorders, and developing therapies that harness that relationship.
The findings were published last week in Nature Neuroscience1.
On the move
Previous studies have found that, under healthy conditions, some types of immune cell found in the gut are also housed in the meninges. But few studies have investigated whether the gut and meninges share immune cells that respond to gastrointestinal infections, says study co-author Menna Clatworthy, a clinician scientist at the University of Cambridge, UK.
Guardians of the brain: how a special immune system protects our grey matter
To find out, Clatworthy and her colleagues infected mice with various pathogens that cause stomach illness, including the food-poisoning bacterium Citrobacter rodentium and Schistosoma mansoni, a parasitic worm that causes a tropical disease called snail fever. The researchers then compared immune cells called CD4+ T cells — which direct other immune cells to fight infections — between the gut and the meninges.
Before infection, CD4+ T cells made up only a small portion of the immune cells found in the meninges. Three weeks after mice were infected with C. rodentium, there was a spike in the number of T cells that expressed a protein called IL-17 in both the gut and the meninges. These types of T cells are known to target C. rodentium. In both tissues, there was also an increase in the number of T cells geared towards fighting parasitic worms six weeks after mice were infected with S. mansoni.
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