Multiple Sclerosis 101: Understanding the Immune System
The immune system is a fascinating and complex thing! In fact, scientists still have a lot to learn about the immune system and autoimmune diseases. We know it plays a role in the development of multiple sclerosis, and in the damage of myelin that occurs in people with MS. This is why many disease-modifying drugs used to treat MS work by manipulating our immune systems. Therefore, I think it’s important to understand at least the basics of the immune system response because it helps to explain what goes wrong in a person with an autoimmune disease such as MS.
How the immune system works
The immune system is the police patrol of the body; its job is to serve and protect you. It constantly works to defend you from foreign invaders that could do damage and/or threaten your life.
White blood cells
White blood cells are like police officers out on foot patrol. They circulate in your bloodstream, constantly scanning for trouble in the streets and looking for foreign invaders.
Other cells have what are called antigens on their surfaces, which act kind of like a photo ID. The patrolling white blood cells can check this ID and tell which cells belong to you, and which do not. If they see a cell whose ID doesn’t check out, they immediately handcuff it by engulfing it and calling for backup. At that point, millions of immunologic cops come running to the fight. The foreign cell’s antigen is then chopped off and taken back to the lymph nodes for investigation.
B and T cells
Lymph nodes are the police precincts of the body, and the police captains are called the B and T cells. B and T cells are made in the bone marrow and mature in the spleen, thymus, and other tissues of the lymphatic system. Once they are alerted that there is a foreign invader, they spring into action. The T cells migrate from the lymph nodes into your circulation to kill off any of your own cells that were infected during the immune response, and direct other cells to the scene of the crime. B cells take the foreign antigen that was seized and use it to create a defensive weapon known as an antibody.
An antibody is specifically designed by your immune system to kill off the particular foreign invader, or pathogen, that it was made from. The B cells then create drones covered in those antibodies and send them to hunt and kill off the pathogen. Interestingly, doctors have used this principle to combat the Ebola outbreak. They took blood containing antibodies from people who had been exposed to Ebola and transfused it into others in an attempt to help their immune systems combat the virus. This obviously has nothing to do with MS, but I thought I would throw that in as an interesting example anyway!
How the immune system overcomes infections
Once your immune system is able to produce antibodies faster then the pathogen can replicate and invade your body, the infection is successfully defeated. The immune system has an excellent memory and can remember which antibodies it needs to produce in order to attack certain targets. The second time our immune system encounters a specific pathogen, the antibodies created during the first exposure are rapidly produced again. This is much more efficient than having to create an entirely new weapon, so the immune response is faster and stronger during each subsequent exposure. Therefore, the immune system is often able to detect and suppress pathogens before they can make you sick.
In autoimmune diseases such as lupus, celiac disease, and multiple sclerosis, the immune system makes a mistake in reading the cell's antigens (their ID). It thinks that the body’s own cells are foreign invaders. The immune system then launches an attack against our own cells like it is trained to do to foreign invaders.
There is a barrier between your circulatory system and your brain (aptly named the blood-brain-barrier), which normally keeps immune cells out of the delicate tissues of the brain. In multiple sclerosis, immune cells make their way through a damaged blood-brain barrier, attack oligodendrocytes (the cells that make myelin) and myelin, and cause central nervous system damage. There is still much we have yet to learn about why this process occurs in the first place, and the exact role it plays in MS. But for now, the most effective method we have of preventing further damage is to use drugs that keep the immune system from mounting an attack on our own cells, and many of these medications work by suppressing the immune system.
What role do vaccines play?
Vaccines are a way of introducing either a weakened or a fake antigen into your body so that your immune system mounts a defense against pathogens like the measles, chickenpox, or the flu. That way, if you are exposed to these diseases at some point in the future, your immune system will remember how to fight them, and use the antibodies from its arsenal to suppress the infection before it makes you sick.
Recommendations on which vaccines are safe for people with MS are updated periodically, so I always consult the National MS Society’s guidelines.
Those are the major principles of the immune response involved in MS. Does anyone have any questions?
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