New role for white blood cells in the developing brain

July 22, 2020

Whether white blood cells can be found in the brain has been controversial, and their role there a complete mystery. In a study published in Cell, an international team of scientists led by Professor Adrian Liston (Babraham Institute, UK & VIB-KU Leuven, Belgium) describe a population of specialised brain-resident immune cells discovered in the mouse and human brain, and show that the presence of white blood cells is essential for normal brain development in mice.

Like a highly fortified headquarters, our brain enjoys special protection from what is circulating in the rest of our body through the blood-brain barrier. This highly selective border makes sure that passage from the blood to the brain is tightly regulated.

The blood-brain barrier also separates the brain from our body's immune system, which is why it has its own resident immune cells, called microglia, which trigger inflammation and tissue repair. Microglia arrive in the brain during embryonic development, and later on, the population becomes self-renewing.

Yet, white blood cells--which are part of our immune system--have been found to play a role in different brain diseases, including multiple sclerosis, Alzheimer's and Parkinson's disease or stroke. Whether or not white blood cells can be found in healthy brains as well, and what they might be doing there, has been subject of intense debate. An interdisciplinary team of scientists led by Prof. Adrian Liston (Babraham Institute and VIB-KU Leuven) set out to find the answers.

White blood cells in the brain

"A misconception about white blood cells comes from their name," explains Dr Oliver Burton (Babraham Institute). "These 'immune cells' are not just present in the blood. They are constantly circulating around our body and enter all of our organs, including--as it turns out--the brain. We are only just starting to discover what white blood cells do when they leave the blood. This research indicates that they act as a go-between, transferring information from the rest of the body to the brain environment"

The team quantified and characterised a small but distinct population of brain-resident T helper cells present in mouse and human brain tissue. T cells are a specific type of white blood cells specialized for scanning cell surfaces for evidence of infection and triggering an appropriate immune response. New technologies allowed the researchers to study the cells in great detail, including the processes by which circulating T cells entered the brain and began to develop the features of brain-resident T cells.

Dr Carlos Roca (Babraham Institute): "Science is becoming increasingly multidisciplinary. Here, we didn't just bring in expertise from immunology, neuroscience and microbiology, but also from computer science and applied mathematics. New approaches for data analysis allow us to reach a much deeper level of understanding of the biology of the white blood cells we found in the brain."

An evolutionary role

When T helper cells are absent from the brain, the scientists found that the resident immune cells - microglia - in the mouse brain remained suspended between a fetal and adult developmental state. Observationally, mice lacking brain T cells showed multiple changes in their behavior. The analysis points to an important role for brain-resident T cells in brain development. If T cells participate in normal brain development in mice, could the same be true in humans?

"In mice, the wave of entry of immune cells at birth triggers a switch in brain development," says Liston. "Humans have a much longer gestation than mice though, and we don't know about the timing of immune cell entry into the brain. Does this occur before birth? Is it delayed until after birth? Did a change in timing of entry contribute to the evolution of enhanced cognitive capacity in humans?"

The findings open up a whole new range of questions about how the brain and our immune system interact. "It has been really exciting to work on this project. We are learning so much about how our immune system can alter our brain, and how our brain modifies our immune system. The two are far more interconnected than we previously thought," says Dr Emanuela Pasciuto (VIB-KU Leuven).

The study also brings in a connection with the gut microbiome, says Liston: "There are now multiple links between the bacteria in our gut and different neurological conditions, but without any convincing explanations for what connects them. We show that white blood cells are modified by gut bacteria, and then take that information with them into the brain. This could be the route by which our gut microbiome influences the brain."

Taken together, the results contribute towards the increasing recognition of the role of immune cells in the brain and shed new light on its involvement in a range of neurological diseases.
-end-


Babraham Institute

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.