Researchers are constantly making new discoveries about Alzheimer’s disease (AD) due to the fact that is a complex condition that involves one of the most sophisticated organs, the brain. In recent years, some of the focus of AD research has shifted to how the immune system and the brain interact with each other, and how this might affect AD. Here is a brief overview of some of the more recent research about AD and the immune system.
Amyloid plaques and the immune system
Researchers at Harvard have been studying a molecule known as amyloid-beta. This molecule is responsible for the amyloid plaques that are found in the brains of patients with dementia.1 Until recently, these plaques were always considered to be a bad waste product of the AD process, but researchers now are beginning to believe that they are part of the body’s innate immune system and actually play a role in protecting the brain.1
Researchers believe that the plaques may form as an immune response to protect the brain from foreign invaders such as bacteria and viruses.1 They propose that plaques form as shields around the pathogens to keep them from attacking the brain. These plaques only appear to become a problem when they begin to overproduce.1 This may be caused by the immune system becoming overactive and mistakenly attacking healthy brain cells, much like other autoimmune disorders such as lupus and rheumatoid arthritis.
While this research has been in progress for over a decade, it still needs to be explored further. It could explain why many drugs aimed at treating amyloid plaques have not been as successful as researchers have hoped, and may lead to new treatments for AD.1,2
The lymphatic system and the brain
For hundreds of years, scientists thought that the brain had a separate immune system from the rest of the body. More recently, researchers have discovered that the brain is connected to the lymphatic system, an important part of the immune system, which is a series of vessels that run throughout the body much like veins and arteries in the circulatory system.3 This means that the brain uses the lymphatic system to remove certain waste products from the brain, and may tie AD with lymphatic drainage disorders.
This research not only changes the way that scientists think about AD and the immune system, but it also changes the whole nature of how researchers look at how the brain and the immune system interact. Knowing that the brain is connected to our lymphatic system may lead to changes in treatments of other diseases such as multiple sclerosis and Parkinson’s disease, as well as AD.3
The immune system and early Alzheimer’s disease
Researchers have been struggling to find medications to effectively treat AD. Most current medications are aimed at reducing beta-amyloid plaques in the brain, but some scientists have noted that there seems to be no connection between an increase in amyloid plaques and an increase in memory loss.2 New studies have begun to look at the loss of synapses, or brain cell connections, in the brains of AD patients.
In normally functioning human brains, there is a process where the immune destroys unnecessary synapses in order to make the brain process information more efficiently.2 This happens commonly in child and adolescent brains, and a protein known as C1q is responsible for signaling the brain to destroy the inefficient synapses. Researchers theorize that people with early stages of AD may have increased amounts of C1q in their brain, which may signal the immune system to destroy needed synapses and not just unnecessary ones.2 Initial studies with mice show potential support for this theory, but much more research is needed to prove this connection.
Other studies of the immune system and AD show a connection between high levels of inflammation markers in the both the blood and the spinal fluid of patients with early stages of AD.4 This study also shows that the brain is much more connected to the immune system than researchers knew in the past, as researchers didn’t expect to find the same level of inflammation in the blood as in the spinal fluid. While these studies are not aimed at the treatment of AD, they may lead to better early diagnosis of AD, leading to earlier and more targeted treatment.4
What does this research mean for the future of Alzheimer’s treatments?
As researchers discover more information about the human brain and how it interacts with the immune system, they pave the way for better treatment options for AD patients. This new research can seem frustrating for AD patients and their loved ones, as it appears to ask more questions than it answers, but it is opening the doors for new or better AD treatments. In addition, this research is not only helping patients with AD, but it is also helping to find causes and treatments for other neurodegenerative diseases and other autoimmune diseases, which may help hundreds of thousands, if not millions of patients around the world.
Hamilton J. NPR Choice page. Npr.org. https://www.npr.org/sections/health-shots/2018/02/18/580475245/scientists-explore-ties-between-alzheimers-and-brains-ancient-immune-system. Published 2018. Accessed June 1, 2019.
Immune system dysfunction may occur early in Alzheimer’s disease. ScienceDaily. https://www.sciencedaily.com/releases/2018/02/180206115411.htm. Published 2018. Accessed June 1, 2019.
Hamilton J. NPR Choice page. Npr.org. https://www.npr.org/sections/health-shots/2017/10/03/555353033/brains-link-to-immune-system-might-help-explain-alzheimers. Published 2017. Accessed June 1, 2019.
Sauer A, Sauer A. Early Alzheimer's Could Be Caused by Immune System. Alzheimers.net. https://www.alzheimers.net/5-11-16-early-alzheimers-caused-by-haywire-immune-system/. Published 2018. Accessed June 1, 2019.