Empowering people affected by MS to live their best lives

The Definition of Multiple Sclerosis

Multiple sclerosis is an immune-mediated disease, meaning an abnormal response of the body’s immune system causes the disease. With MS, the immune system attacks the central nervous system — which is made up of the brain, spinal cord and optic nerves — and creates an inflammatory response.People with MS typically experience one of four types of MS:

Clinically isolated syndrome (CIS)
Relapsing-remitting MS (RRMS)
Secondary progressive MS (SPMS)
Primary progressive MS (PPMS)

See how MS affects the human body.

Results of the Immune System Attack

Typically, your immune system protects you from diseases and infections by attacking viruses and bacteria that get into your body. In MS, something triggers the immune system to attack the central nervous system.When a person is living with MS, their immune system attacks and damages:

Myelin, the fatty substance that surrounds and insulates the nerve fibers
Axons, long, threadlike parts of a nerve cell
Oligodendrocytes, the cells that make myelin

This attack produces inflammation, and:

Damages or destroys myelin and oligodendrocytes
Causes damage to the axons
Produces damaged areas (lesions or scars) in the CNS (brain, spinal cord and optic nerves), which can be detected on magnetic resonance imaging (MRI)
Slows or halts nerve conduction — producing the neurologic signs and symptoms of MS

Myelin is present in the central nervous system and peripheral nervous system. However, only the central nervous system is affected by MS.In MS, the immune system primarily attacks the myelin sheath that surrounds the axons. This sheath protects the axons much as insulation around an electrical wire protects the wire. If the myelin sheath is damaged, nerve signals will travel more slowly or be blocked completely. Without myelin to protect the nerve fibers, they are also damaged.The damage to the myelin and the failure to replace it is called demyelination.

In a normal nerve, the sheath is not damaged. Here, bits of that sheath appear to have been eaten away.

The damaged areas develop scar tissue, or sclerosis. When the axon is damaged or severed, messages no longer travel efficiently between the brain and the body. This causes the symptoms of MS, including vision problems, walking or gait difficulties, and cognitive changes.Myelin has some ability to repair itself, and researchers are looking for ways to restore what has been lost in people with MS. However, axons cannot be repaired.Because damage to axons can occur even in the earliest stages of the disease, early treatment with a disease-modifying therapy is important.The number of lesions and the areas of the central nervous system that are damaged affect the type and severity of MS symptoms.

T Cells and B Cells

Many different cells are involved in the abnormal immune response seen in MS. Two important types of immune cells are T cells and B cells.T cells become activated in the lymph system and, in MS, enter the central nervous system through blood vessels. Once there, T cells release chemicals that cause inflammation and damage. This results in damage to myelin, nerve fibers and the cells that make myelin. T cells are also important to help activate B cells and call on other immune system cells to participate in the immune attack.T regulatory cells, a type of T cell, dampen or turn off inflammation. In MS, T regulatory cells do not function correctly and do not effectively turn off inflammation. Cytotoxic or “killer” T cells directly attack and destroy cells bearing certain characteristics.B cells in MS can cause damage in the central nervous system through the production of antibodies and by stimulating other proteins. B cells become activated with the help of T cells.

The Cause of MS

The cause of MS is unknown, but it is believed that genetic susceptibility, infectious disease and environmental factors combine to trigger the disease.In many autoimmune diseases, researchers have identified the specific antigen that is responsible. While most experts believe MS is an autoimmune disease, no specific antigens have been identified.

Disease-Modifying Therapies

Medications that target the parts of the immune response in MS that cause inflammation and damage have been shown to reduce the accumulation of new lesions. There are now many different disease-modifying therapies (DMTs) available that help modify the MS disease course and prevent the demyelination that causes MS relapses, disease progression and disability.Disease-modifying therapies for MS work by various mechanisms, with different therapies having different mechanisms of action. These mechanisms include:

Interfering with the activation of T cells
Reducing inflammation and immune activity
Blocking the movement of immune system cells and limiting entry of immune cells into the central nervous system
Depleting the numbers of immune system cells

In addition, the body heals some lesions naturally by stimulating oligodendrocytes in the area or by recruiting young oligodendrocytes from further away. This allows the body to begin making new myelin at the damaged site. However, this natural repair process is slow and incomplete.More studies are needed to understand the remyelination process and develop treatments to repair damage.There are over a dozen treatments to help modify the MS disease course, and MS researchers are working to discover how to stop disease progression, restore lost function and end MS forever. Explore research progress.

T Cells and B Cells

The Cause of MS

Disease-Modifying Therapies

Interfering with the activation of T cells
Reducing inflammation and immune activity
Blocking the movement of immune system cells and limiting entry of immune cells into the central nervous system
Depleting the numbers of immune system cells

How MS Affects the Brain

The Definition of Multiple Sclerosis

Results of the Immune System Attack