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Study Finds Essential Role of White Blood Cells in Normal Brain Development

International team of scientists discover the presence of white blood cells to play key roles in normal brain development in mice models.

The blood-brain barrier separates the brain from our body’s immune system, it is a highly selective border that ensures tight regulation of blood to the brain. Immune cells in the blood-brain barrier, microglia, which trigger inflammation and tissue repair are known to arrive in the brain during embryonic development.

White blood cells 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.

In a study published by an international team of scientists led by Professor Adrian Liston, Babraham Institute, UK & VIB-KU Leuven, Belgium set out to 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.

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.

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 foetal and adult developmental state. Mice lacking brain T cells were observed to display multiple changes in their behaviour. The analysis points to an important role for brain-resident T cells in brain development and questions whether it could also be applicable to human brains.

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,” said Dr Emanuela Pasciuto, VIB-KU Leuven.

Professor Liston also sheds light on how this study brings in a connection with the gut microbiome. “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.” [APBN]