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In the autoimmune disease multiple sclerosis (MS), the immune system mistakenly attacks the central nervous system (CNS). The CNS includes the brain, spinal cord, and optic nerves.
The immune attack damages the protective covering around nerves and can disrupt nerve signals, causing a wide range of symptoms. This article explains which immune cells are involved, how inflammation harms the nervous system, and why MS symptoms depend on where the damage occurs.
Normally, your immune system protects you by recognizing and attacking germs and other harmful invaders. To do this safely, your immune system has to tell the difference between your own healthy tissue and foreign threats. This ability to avoid attacking your own tissues is known as immune tolerance.
In MS, immune tolerance no longer works as it should. Your immune system mistakes part of your CNS for a threat, then attacks it. This MS immune response involves several types of immune cells working together.
Researchers have learned much about this process by studying an animal model of MS called experimental autoimmune encephalomyelitis. Scientists still don’t fully understand how MS develops, but they’ve identified several key immune cells involved in MS inflammation and damage.
T cells are immune cells that help recognize and respond to potential threats. They identify specific molecules, called antigens, that signal a cell or substance may be harmful.
Once activated, T cells can multiply and call other immune cells into action. Several types of T cells are involved in MS, including helper T cells, killer T cells, and regulatory T cells.
Helper T cells organize the immune response. Rather than attacking cells directly, they send signals that activate and recruit other immune cells.
Killer T cells, also called cytotoxic T cells, directly destroy cells they identify as threats.
In MS, some T cells mistakenly react to myelin, even though it is part of the body’s own nervous system. Myelin is a fatty, protective coating around nerve fibers in the brain and spinal cord.
Like insulation around an electrical wire, myelin helps nerve signals travel quickly and efficiently. When immune attacks damage myelin, those signals may slow down or become disrupted.
Both helper and killer T cells have been found in MS lesions (areas of damage in the brain or spinal cord). Researchers have also found activated T cells that react to myelin in the cerebrospinal fluid, the liquid surrounding the brain and spinal cord, of people with MS.
Regulatory T cells help keep immune activity under control. They act like the immune system’s brakes, helping prevent attacks on healthy tissue.
In people with MS, regulatory T cells may not work as well as they should. This may allow harmful immune activity and inflammation in the brain and spinal cord to continue.
B cells are another key part of the MS immune response. They produce antibodies — proteins that attach to specific targets and mark them for destruction.
In MS, some B cells produce antibodies that target myelin or other parts of nerve cells by mistake. These are called autoantibodies because they react against the body’s own tissues. B cells also act as messengers, presenting pieces of myelin to T cells and activating them, which strengthens the immune attack on the CNS.
Treatments that reduce B cell numbers have been shown to lower MS relapse rates. This is some of the strongest evidence that B cells, along with T cells, play a major role in MS damage.
This finding shifted how researchers think about MS. For many years, scientists focused mostly on T cells. Now, B cells are recognized as an important treatment target.
Macrophages are immune cells that clean up damaged tissue, cellular debris, and dead cells throughout the body. Unlike T cells and B cells, macrophages don’t need to identify a specific invader before they act. Instead, they detect general patterns shared by harmful invaders, allowing them to respond quickly to different threats.
Macrophages also release chemical messengers called cytokines, which increase inflammation and recruit even more immune cells to the area. In MS, macrophages gather in inflamed areas of the brain and spinal cord. There, they release cytokines and help break down myelin.
Researchers continue to study exactly how macrophages interact with T cells and B cells during an MS attack.
Inflammation is the body’s natural response to injury or infection, and it usually helps protect you and support healing. In MS, however, inflammation occurs in the brain and spinal cord and damages healthy nervous system tissue. This is called neuroinflammation.
Sudden increases in inflammation can cause an MS relapse. During a relapse, new symptoms may appear, or existing symptoms may get worse over a short period.
Relapses are often the most noticeable sign of MS activity. However, inflammation may also continue even when a person is not experiencing an obvious relapse.
Low-level inflammation may continue quietly in the CNS between relapses. Researchers sometimes call this smoldering inflammation.
Over time, ongoing inflammation may contribute to nerve damage and gradually worsening disability. Researchers call worsening that occurs without a relapse progression independent of relapse activity (PIRA).
Scientists are still studying how chronic inflammation and PIRA contribute to long-term MS progression.
The location and severity of immune attacks within your CNS determine which symptoms you experience. Demyelination — the loss or damage of myelin — can disrupt different functions depending on where it occurs in the brain or spinal cord. This is why MS symptoms can look so different from person to person.
When immune attacks damage myelin in the brain, you may have problems with thinking, memory, concentration, coordination, or mood, including depression, as well as fatigue. Damage to areas that control movement can also cause muscle weakness, tremors, or trouble with balance and walking.
The specific changes you notice depend on which brain regions are affected because different areas control different functions.
The spinal cord carries signals between your brain and the rest of your body. When immune attacks damage myelin here, the spinal lesions may cause muscle weakness, numbness, or tingling sensations, often in your arms or legs. Spinal cord damage can also lead to spasticity (muscle spasms or stiffness) and bladder or bowel problems.
Some people also notice an electric shocklike sensation that runs down the spine when they bend their neck forward. Called Lhermitte’s sign, this symptom happens because the spinal cord is especially sensitive to even small areas of demyelination.
The optic nerve carries visual information from your eyes to your brain. Inflammation of this nerve, called optic neuritis, can cause blurred vision, eye pain that worsens with movement, or temporary vision loss in one eye.
Colors may also look duller or less vivid than usual. For many people with MS, optic neuritis is the first sign of the disease and may appear before other symptoms develop.
Because immune attacks can occur almost anywhere in the CNS, no two people experience the same combination of MS symptoms. Your symptoms depend on where and how severely your immune system has caused damage.
Understanding this connection between immune attacks and symptoms is an important part of understanding MS, and researchers continue to learn more about how the disease develops.
On MyMSTeam, people share their experiences with multiple sclerosis, get advice, and find support from others who understand.
Has learning more about how MS affects your immune system changed the way you think about your symptoms? Let others know in the comments below.
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Tenho E. M. há 36 anos,desde os 12 anos de idade
Os problemas que tenho são
-incontinência urinária
-obstipação
- espasticidade muito forte nos membros inferiores.
Tenho sido medicado com Ocrevus… read more
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