The immune system is central to myasthenia gravis (MG). MG is an autoimmune disease, meaning it involves the immune system mistakenly attacking the body’s own healthy cells, tissues or proteins instead of outside invaders, like germs or viruses. In MG, the body produces antibodies that target proteins of the neuromuscular junction.
How does MG affect the immune system?
The immune system protects the body against invaders like viruses and bacteria, called antigens. Normally, a special type of white blood cell called a B cell helps defend against these invaders. When a B cell encounters an antigen, it creates antibodies (called immunoglobulins), which are proteins that that latch on to the foreign invaders, blocking them from entering cells and neutralizing the threat.
In MG, the immune system mistakenly produces antibodies that block or destroy the muscles’ receptor sites, damaging how signals travel between the nerves and muscles. This causes the muscles to weaken.
These antibodies are not the same in all patients:
- Around 85% of people with MG have antibodies that target the muscle acetylcholine receptor (AChR-MG), affecting the part of the nerve cells that send signals from nerves to muscles.
- About 5% have autoantibodies against the protein muscle specific-kinase (MuSk-MG), inhibiting normal neuromuscular signaling.
- About 10% of patients with MG have neither anti-AChR nor anti-MuSK antibodies. Patients in this category may have rare antibodies known to cause MG (like those that target lipoprotein receptor-related protein 4), but they might also have antibodies that researchers haven’t yet connected to MG, or antibodies that aren’t detectable with current testing methods.
Read more about MG causes and risk factors
How do treatments impact the immune system?
Many treatments for MG work by lowering the immune system’s impact on the body.
One example is corticosteroids and other immunosuppressants, such as mycophenolate mofetil or azathioprine. Immunosuppressants reduce the activity of the immune system. For example, they may reduce the number of T cells or B cells your body produces, which helps limit the number of antibodies that target the proteins of the neuromuscular junction.
Another is plasma exchange, which filters the autoantibodies that drive MG out of the bloodstream and temporarily reduces symptoms, until the body creates more autoantibodies.
Intravenous immunoglobulin adds antibodies from healthy donors to your bloodstream. Among other impacts on the immune system, this reduces the levels of antibodies that cause MG.
Thymectomy — removing the thymus gland — also impacts the immune system, as this is where the body’s T cells are made.
The choice of treatment will depend on the antibodies you test positive for, as well as the function of the thymus gland and many other factors.
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