A group of immune cells that normally protect against inflammation in the gastrointestinal tract may have the opposite effect in multiple sclerosis (MS) and other brain inflammation-related conditions, according to a new study by Weill Cornell Medicine and NewYork-Presbyterian researchers. The results suggest that countering the activity of these cells could be a new therapeutic approach for such conditions.
The researchers, who reported their finding Dec. 1 in Nature, were studying a set of immune cells called group 3 innate lymphoid cells (ILC3s), which help the immune system tolerate beneficial microbes and suppress inflammation in the intestines and other organs throughout the body. They discovered a unique subset of these ILC3s that circulate in the bloodstream and can infiltrate the brain—and, to their surprise, do not quench inflammation but instead ignite it.
The scientists called this subset inflammatory ILC3s, and found them in the central nervous system of mice with a condition modeling MS. Instead of constraining the immune response, this subset of ILC3s spurred another group of immune cells called T cells to attack myelinated nerve fibers, leading to MS-like disease symptoms. The researchers detected similar inflammatory ILC3s in the peripheral blood and cerebrospinal fluid of MS patients.
“This work has the potential to inform our understanding of, and potential treatments for, a broad variety of conditions involving T-cell infiltration of the brain,” said senior author Dr. Gregory Sonnenberg, associate professor of microbiology and immunology in medicine in the Division of Gastroenterology and Hepatology and a member of the Jill Roberts Institute for Research in Inflammatory Bowel Disease at Weill Cornell Medicine.
Dr. Greg Sonnenberg (left) and John Benji Grigg
MS affects more than two million people worldwide. Other conditions that feature chronic brain inflammation afflict tens of millions more and include Alzheimer’s and Parkinson’s diseases. There is also evidence that neuroinflammation develops naturally with aging and is a major factor in age-related cognitive decline, and more recently inflammatory T-cell responses in the brain have been linked to neurological symptoms associated with SARS-CoV-2 infection.
The researchers have shown in recent work that ILC3s residing in the gut act as sentinels and immune regulators, suppressing inflammation—including inflammatory T-cell activity—and warding off cancer. In the new study, they examined the roles of ILC3s in the brain, and found, contrary to their expectation, that ILC3s are not normally present in the brain under healthy conditions but can infiltrate the brain from the bloodstream during inflammation. When they do infiltrate the central nervous system, they have pro-inflammatory rather than anti-inflammatory effects.
The researchers showed with a mouse model of MS that these inflammatory ILC3s in the brain function as antigen-presenting cells: They display bits of myelin protein, the main ingredient in the insulating layer around nerve fibers, to T cells—prompting them to attack myelin, causing the nerve damage that gives rise to disease signs. They found the inflammatory ILC3s in close association with T cells in regions of active inflammation and nerve damage in the mouse brains. To read more, click here.