The brain has a special kind of memory for past infections

The brain and spinal cord have their own squad of specialized immune cells, but the peripheral immune system is armed with a larger battalion of proteins, cells, and the entire organ, such as the spleen, that prevent invaders. Over the last decade, researchers have found that the peripheral immune system affects neural activity, that is, how immune signals generated from outside the central nervous system affect cognitive processes, social behavior, neural degeneration, and more. We have made great strides in understanding this. In fact, they learned that peripheral immune cells regularly patrol the central nervous system and support its function. In a new study, researchers can remember people, places, smells, etc., just as the brain remembers people, places, smells, etc. Preserves what they call “traces of memory” of past infections in the body.. Reactivating the same brain cells that encode this information is sufficient to quickly summon the peripheral immune system to protect at-risk tissue.

In a sense, this is not a complete surprise. It is clear that the peripheral immune system can retain information about past infections and fight future infections. Otherwise, the vaccine will not work. However, Asya Rolls, a neuroimmunologist at the Technion-Israel Institute of Technology and lead author of the paper, states that the study extends this notion of classical immunological memory. Initially, she was surprised that the brain could store traces of immune activity and use them to provoke such accurate responses. “I was surprised,” she says.

Rolls’ team focused on an area of ​​the brain called the insular cortex. The insular cortex senses the internal state of the body through visceral signals such as temperature, pain, hunger, and possibly immune activity. They studied strains of mice with a type of intestinal inflammation known as colitis and used fluorescent markers to take snapshots of groups of brain cells in the insular cortex that became active during infection. rice field.

After the infection and immune response disappeared, the researchers injected mice with a drug that artificially reactivated the same group of brain cells. They were amazed at what they saw: upon reactivation, the insular cortex instructed the immune system to initiate a targeted response in the intestine at the site of the original inflammation-there was no infection by that time. but, Local inflammation caused by tissue damage or pathogens can be found. The brain retained some memory of the infection and was ready to resume the fight.

“This result surprised us because we didn’t really expect it,” said Tamar Koren of Technion, the lead author of the paper. “I think this was our moment.”

Repeated experiments in mice with peritoneal infection gave similar results. However, it was still unclear how the insular cortex communicates with organs to promote an immune response.

To begin answering that question, researchers used a fluorescent tracer to graph the neural connections that allow the brain to exchange messages with the intestines and abdominal cavity. However, Koren considers this route to be just one line of communication. She also says that the insular cortex may regulate hormone levels to help signal the inner layers of tissues in the body and reactivate the immune response.

The insular cortex was a good place to start, although additional brain areas may be working, said Kevin Tracy, director of the Feinstein Institute of Medicine and neurosurgeon who was not involved in the study. Says. Tracey showed in the 1990s that certain nerves connected to the brainstem can talk to peripheral immune cells and weaken the immune response before it damages the body. This phenomenon is currently Inflammatory reflexWas the first evidence that neural circuits could control the peripheral immune system.And now Used for treatment Autoimmune diseases such as rheumatoid arthritis.

New studies provide “non-attackable” evidence that the central nervous system can control the peripheral immune system, Tracy says. “This is a very important contribution to the fields of neuroscience and immunology.”

Tracey suspects that there may be a similar neurological “map” of immunological information, just as researchers tracked sensory and motor processing to specific brain regions. He says this new study is the first direct evidence of the map. “It will be really exciting to see what happens next,” he adds.

Rolls’ lab has already begun to devise clinical trials to treat chronic intestinal inflammation, based on the team’s findings. Many bowel disorders, such as inflammatory bowel disease, are caused by stress and strong emotions. Researchers believe that this causes neurons in the insular cortex to misfire, reactivate immunological memory, and cause a false immune response. They can successfully reduce colitis in mice by simply reducing the activation of the insular cortex, placing human patients in a functional magnetic resonance imaging device and consciously reducing activity in that area. I suspect I can teach you. Reduces drug dependence and relieves intestinal inflammation. Rolls explains that allowing the brain to react instead is the most balanced and personalized reaction her team can seek.