Miniscule cleaners
February 12, 2024
This article originally appeared in Dutch in EOS Magazine. Read more at eoswetenschap.eu.
Microglia are specialized immune cells that play both soldier and feeder roles. The Pac-Man of our brains, you could say. They eliminate foreign and other threatening substances by engulfing them, thus contributing to keeping the brain healthy.
Immunity in the brain
Our brain is a complex organ composed of 150 to 170 billion cells. The first described and most well-known brain cells are our neurons, the cells that receive, process, and transmit information. They contribute to controlling our body and cognitive functions. However, these neurons make up only about half, or 86 billion, of the total number of brain cells. The other half, or 85 billion cells, are collectively known as glia (Greek for glue). Glia are considered support cells, providing support to the neurons. They can be divided into three cell types: astrocytes, oligodendrocytes, and microglia. Astrocytes contribute to energy and support neuron communication. Oligodendrocytes contribute to the speed of neurons. The latter, our microglia, are the immune cells of the brain.
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What microglia do
Microglia are essential for brain development, maintaining brain health, and protection. The first form of brain protection is the blood-brain barrier. This physical barrier or blockade ensures that nothing enters the brain through the bloodstream. A second protective mechanism are the microglia. They provide active protection against infections that have managed to breach the barrier. Additionally, they contribute to waste disposal in the brain, ensuring that dead cells and other debris are cleared away. Microglia continuously scan the environment, extending their long arms in all directions, ready to react if necessary.
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Microglia in case of disease
While microglia protect our brain, they can also contribute to neurodegenerative diseases such as Alzheimer's and Parkinson's. The exact mechanism by which they contribute is not yet known, but microglia either stop responding to their environment or go into an overreaction. Both of these scenarios are harmful to the normal functioning of the brain.
Overactivity is observed, for example, in Alzheimer's disease, where cells come into contact with beta-amyloid brain plaques. The cells become active and attempt to break down these plaques. While initially, clearance of plaques is beneficial for our brains, over time, this reaction proves to do more harm than good. After a prolonged period of inflammation, we observe that microglia also contribute to the breakdown of healthy brain cells. Microglia responding to beta-amyloid brain plaques not only participate in clearing but also emit signals. In doing so, they release substances that aid in the clearance but can also send a kind of danger signal to other cells. The signal spreads throughout the brain, eventually resulting in a malfunctioning immune system of the brain.
It is crucial to continue researching how cells in our brain interact and how this changes in diseases. Finding a way to intervene in the immune system in the brain could potentially serve as the basis for a new therapy.
Baukje Bijnens, a PhD student at the VIB-UAntwerp Center for Molecular Neurology, focuses on neuroinflammation in Alzheimer's disease, contributing valuable insights to this field of research.
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