Scientists are exploring a little-known protein that may help explain how brain chemistry, immune cells and nerve-cell connections influence behavior.
The protein, called IDO2, plays a role in how the body processes tryptophan, an amino acid found in protein-rich foods. A new study suggests that losing this protein can produce major changes in the brains and behavior of mice.
The research was led by Associate Professor Yasuko Yamamoto and colleagues at Fujita Health University in Japan. Their findings were published in The FEBS Journal. The study may offer a new clue for understanding complex brain conditions, although the researchers stress that findings in mice cannot be directly applied to people.
Tryptophan is best known as a building block that the body needs to make proteins, but it can also be turned into several other chemicals. One important route is called the kynurenine pathway. Chemicals produced during this process can affect the brain, the immune system and the way nerve cells communicate.
Earlier studies have connected changes in this pathway with conditions including schizophrenia, Alzheimer’s disease and autism spectrum disorder. However, scientists still do not fully understand how individual proteins in the pathway affect the brain. IDO2 has received much less attention than some related proteins.
To investigate its role, the researchers studied mice that had been genetically changed so they could not produce IDO2. They compared these animals with ordinary mice in a series of behavioral tests. Mice without IDO2 showed more repetitive grooming, explored less and had more difficulty adjusting when their surroundings changed.
The animals also behaved differently in tests involving contact with other mice. Researchers described some of these patterns as autism-like because they resemble certain behaviors used in laboratory studies of autism. This does not mean that the mice had human autism or that losing IDO2 has been proven to cause autism in people.
The team then examined the animals’ brains to find possible reasons for the behavioral changes. Without IDO2, levels of chemicals involved in tryptophan processing changed. The researchers also found differences in dopamine in areas including the striatum and amygdala.
Dopamine is a chemical messenger that allows brain cells to send signals to one another. It helps control movement, motivation, learning and responses to rewards. Changes in dopamine activity can therefore affect behavior in many different ways.
Another finding involved a protein called BDNF, which helps nerve cells grow, survive and form strong connections. Mice without IDO2 had lower levels of BDNF and changes in tiny structures on nerve cells called dendritic spines. These small structures help nerve cells receive messages from other cells and are important for learning and brain communication.
The scientists also found differences in microglia, special immune-related cells that live in the brain. Microglia normally watch their surroundings, remove damaged material and respond when something goes wrong. In mice lacking IDO2, more of these cells appeared to be in an active state.
Importantly, the researchers later restored IDO2 activity in experiments. Some of the unusual behaviors improved after the protein was restored. This result strengthened the evidence that IDO2 itself was involved in the changes seen in the animals.
The researchers also examined genetic information from 309 people with autism and found an IDO2 mutation in one 16-year-old girl. A single case cannot show that this gene commonly causes autism, and autism has many different genetic and environmental influences. Still, the finding gives scientists another reason to study IDO2 in much larger groups of people.
The study is an early step rather than evidence for a new treatment. Future research will need to determine whether IDO2 has a meaningful role in human brain development or conditions such as autism. Understanding the protein could eventually reveal more about how tryptophan processing, dopamine, nerve-cell growth and the brain’s immune system work together.
If you care about health, please read studies that vitamin D could help lower the risk of autoimmune diseases, and drug for inflammation may stop spread of cancer.
For more health information, please see recent studies about which drug can harm your liver most, and results showing this drug can give your immune system a double boost against cancer.
Copyright © 2026 Knowridge Science Report. All rights reserved.
