Pathophysiology Of Multiple Sclerosis

What is multiple sclerosis?

Multiple sclerosis is a chronic disease that is non-contagious. It predominantly affects the brain and the spinal cord. It is mainly characterized by a wide variety of neurological symptoms that are caused by the demyelization of the neurons. Moreover, it is an autoimmune disease in which the body’s very own immune system attacks the central nervous system’s cells and underlying tissues.

What causes it?

The ultimate cause of multiple sclerosis remains unknown. This means that multiple sclerosis is an idiopathic disease. According to scientific research, some viral infections or other environmental factors related to childhood are able to trigger the abnormal reactions associated with the immune system.

On a molecular level, a structural similarity can be discovered between an infectious agent that is not identified and some components of the central nervous system. This similarity causes confusion in the immune system’s fighter cells when the body matures later as the body ages. This whole process is termed as molecular mimicry. And since there is no such thing as a multiple sclerosis virus, it can be declared that the disease is not at all contagious.

Where the WBC come in

The body’s white blood cells, more commonly referred to as WBC, have a special subset of cells termed as T cells. These T cells are key players in the development of multiple sclerosis. Normally, these lymphocytes have the ability to differentiate substances or components that belong to the body from those that are foreign. Whenever a foreign body is recognized, the whole immune system is put on alert and the body’s fighter cells attack the foreign body to maintain homeostasis within the body.

However, since multiple sclerosis is an autoimmune disease, it tends to attack itself. The T cells recognize the healthy parts of the central nervous system as something harmful and foreign and attack them as if it is a response aimed at a virus or bacteria.

The T cells attack predominantly attack the myelin which insulates the axons of the nerve cells. This fatty substance is very important, especially when it comes to proper nerve conduction.

About the BBB

There is a normal barrier that goes between the blood and the brain that medical professionals have coined as the blood-brain barrier or the BBB. This BBB is made up of endothelial cells that line the blood vessel walls.

It is during multiple sclerosis that the BBB breaks down and the auto-reactive T cells enter the BBB, when they are clearly not supposed to. After crossing the BBB, the T cells then trigger an inflammatory response that is further mediated by other immune cells namely the cytokines and antibodies. After further inflammatory responses, there is a much bigger opening of the BBB and a wide variety of symptoms are produced.

Moving on, the macrophages are alerted, there is an activation of the MMPs, including other proteases. In short, this all leads to the destruction of the myelin, a process that is termed as demyelization.