Multiple Sclerosis: How the Immune System Attacks the Nervous System

Multiple sclerosis isn’t just a neurological condition-it’s an inside job. Your own immune system, designed to protect you, turns against your brain and spinal cord. It sees the protective coating around your nerves as a threat and starts tearing it apart. That coating? Myelin. And when it’s gone, signals between your brain and body get scrambled. That’s when numbness, vision loss, fatigue, or trouble walking shows up-not because of injury, but because your body attacked itself.

What Happens When the Immune System Goes Rogue

In multiple sclerosis, the immune system launches a targeted assault on the central nervous system. The main target? Myelin, the fatty sheath that wraps around nerve fibers like insulation on an electrical wire. Without it, nerve signals slow down or stop entirely. This isn’t random damage. It’s precise. Immune cells-mainly T cells and B cells-cross the blood-brain barrier, a normally tight seal that keeps harmful substances out of the brain. Once inside, they recognize myelin as foreign and begin attacking.

Research shows that in people with MS, these immune cells don’t just wander in. They’re activated elsewhere in the body, often triggered by environmental factors like the Epstein-Barr virus. Once they enter the CNS, they recruit more immune troops: macrophages, microglia, and dendritic cells. These cells release inflammatory chemicals that turn the area into a war zone. The result? Inflammation, swelling, and the destruction of myelin. Over time, the nerves themselves start to fray and die.

The Four Patterns of Damage

Not all MS is the same. Scientists have identified four distinct patterns of tissue damage in the brain and spinal cord. Pattern I is mostly T cells and macrophages chewing through myelin. Pattern II adds antibodies to the mix-like the immune system is using a missile instead of a knife. Pattern III shows a different story: oligodendrocytes, the cells that make myelin, are dying off first. And Pattern IV? That’s the most alarming. Oligodendrocytes are damaged, but there’s no sign of immune cells nearby. It suggests something deeper is broken in the brain’s ability to repair itself.

These patterns help explain why some people respond to certain treatments and others don’t. If your MS looks like Pattern II, drugs that target antibodies might help. If it’s Pattern III, the focus needs to shift to protecting or replacing myelin-making cells. This is why one-size-fits-all treatments often fail.

Why Women Are More Affected

Women are two to three times more likely to develop MS than men. That gap is wider in places like Canada and Scandinavia, where rates can hit 140 cases per 100,000 people. Why? It’s not just hormones. While estrogen and progesterone play a role in immune regulation, the bigger story involves genetics and environment. Women’s immune systems tend to be more reactive-a trait that helped our ancestors survive infections during pregnancy. But that same sensitivity makes them more vulnerable to autoimmune misfires.

Add in vitamin D deficiency (common in northern latitudes), smoking, and Epstein-Barr virus exposure, and you’ve got a perfect storm. People who carry certain genes like HLA-DRB1*15:01 and get infected with EBV before age 20 have a 32-fold higher risk of developing MS. It’s not one thing. It’s a chain reaction.

Three patterns of MS damage visualized in the spinal cord: cells, missiles, and crumbling oligodendrocytes.

What You Feel When the Nerves Are Under Attack

Symptoms aren’t random. They map directly to where the damage happens. If the optic nerve is hit, you get optic neuritis-vision blurs, colors fade, pain shoots behind the eye. That’s not an eye problem. That’s an immune attack on the nerve connecting your eye to your brain.

Fatigue? It affects 80% of people with MS. It’s not just tiredness. It’s like your body’s battery is draining even when you’re sleeping. That’s because your nerves are working overtime to send signals without myelin. Every movement, every thought, costs more energy.

Numbness or tingling? That’s demyelination in the spinal cord. Walking becomes harder because your brain can’t tell your legs where to move. Lhermitte’s sign-the electric shock feeling when you bend your neck-is a classic sign. It means your cervical spine is damaged. When you move, the exposed nerve fires off a jolt of electricity.

And it’s not just physical. Brain fog, depression, and trouble concentrating are common. The immune system isn’t just attacking nerves-it’s changing how the brain functions.

How Treatments Fight Back

Today’s MS treatments don’t cure the disease. But they stop the immune system from doing so much damage. Disease-modifying therapies (DMTs) are the backbone of care. Ocrelizumab, for example, targets CD20+ B cells. In clinical trials, it cut relapses by 46% and slowed disability progression by 24% in primary progressive MS. Natalizumab blocks immune cells from crossing the blood-brain barrier. It reduces relapses by 68%, but carries a rare but serious risk: progressive multifocal leukoencephalopathy (PML), a brain infection caused by a dormant virus reactivating.

Newer drugs like siponimod and cladribine work differently. They trap immune cells in lymph nodes or wipe out overactive ones. Each drug has trade-offs. Some require regular infusions. Others are pills with strict monitoring. The goal isn’t just to reduce flares-it’s to prevent long-term disability.

A woman's brain showing fading nerves with one molecule sparking new myelin growth in dim light.

The Hope for Repair

The biggest breakthroughs might come from repair, not just suppression. For decades, scientists thought the brain couldn’t fix itself after myelin damage. Now we know it can-but only if the environment allows it. In relapsing-remitting MS, the brain tries to remyelinate. But the inflammation is too toxic. Oligodendrocyte precursor cells sit idle, waiting for the right signal.

Clemastine fumarate, a common antihistamine, showed promise in a phase II trial. It improved nerve signal speed by 35% in people with MS. That’s not a cure. But it’s proof the brain can heal-if we give it the right conditions.

Researchers are now testing drugs that block specific inflammatory signals like IL-21 and TNF-α. Others are exploring stem cell therapies to rebuild myelin. And biomarkers like serum neurofilament light chain (sNfL) are helping doctors see inflammation before symptoms appear. If sNfL levels rise above 15 pg/mL, it means active damage is happening-even if the patient feels fine.

What’s Next

The future of MS care is personal. No two people have the same immune profile. Soon, doctors may test your blood for specific immune cell signatures, viral exposure history, and genetic markers to choose your treatment before you even have a relapse. The International Progressive MS Alliance has poured $65 million into research since 2014. Projects are underway in 14 countries, studying how dendritic cells present myelin to T cells, how neutrophil traps break down the blood-brain barrier, and why some people progress while others stay stable.

The message is clear: MS isn’t just a disease of the nervous system. It’s a disease of immune miscommunication. And the best way to stop it isn’t to suppress the whole system-it’s to teach it what not to attack.

Living With MS Today

People with MS are living longer, healthier lives than ever before. In the past, half of untreated RRMS patients needed a cane or walker within 15 to 20 years. Today, with early treatment, that number has dropped to about 30%. Many stay active, work full-time, raise families. It’s not easy. But the tools are better. The science is faster. And the understanding of what’s really happening inside the body has never been clearer.

It’s still a battle. But now, the body’s own defenses aren’t always the enemy. Sometimes, they’re the key to healing-if we know how to listen.

Is multiple sclerosis hereditary?

MS isn’t directly inherited like a genetic disorder, but having a close relative with MS increases your risk. If a parent or sibling has it, your chance rises to about 2-5%, compared to 0.1% in the general population. Specific genes like HLA-DRB1*15:01 play a role, but they only raise risk if combined with environmental triggers like Epstein-Barr virus or low vitamin D. No single gene causes MS-it’s a mix of biology and environment.

Can you get MS from a virus?

You can’t catch MS like a cold, but the Epstein-Barr virus (EBV)-which causes mononucleosis-is the strongest known trigger. People infected with EBV are 32 times more likely to develop MS. The virus doesn’t cause MS directly. Instead, it may confuse the immune system into attacking myelin because parts of the virus look similar to proteins in the nervous system. Nearly everyone with MS has had EBV, but most people who’ve had EBV never develop MS.

Does vitamin D help prevent or treat MS?

Low vitamin D levels are linked to a higher risk of developing MS, especially in regions far from the equator. People with serum levels below 50 nmol/L have a 60% higher risk. While taking vitamin D supplements won’t cure MS, maintaining levels above 75 nmol/L may reduce relapse rates and slow progression. Many neurologists recommend 2,000-5,000 IU daily, especially in winter months. It’s not a treatment, but it’s a proven supportive factor.

Can MS be cured?

There’s no cure for MS yet. But modern disease-modifying therapies can stop or significantly slow damage in most people. Some patients who start treatment early show no new lesions on MRI for over a decade. In rare cases, people with aggressive MS have had their immune systems reset through stem cell transplants, leading to long-term remission. Research into remyelination and immune tolerance is advancing fast-so while there’s no cure today, the path to one is clearer than ever.

Why do MS symptoms come and go?

In relapsing-remitting MS, symptoms flare up during active inflammation and improve when it calms down. This happens because the immune system attacks myelin in bursts. During a relapse, swelling and inflammation block nerve signals. When the attack ends, the swelling goes down, and nerves can sometimes reroute signals around damaged areas. But each attack leaves behind some permanent damage. Over time, these small losses add up, which is why some people eventually move into a progressive phase where symptoms steadily worsen.

Are MS treatments safe long-term?

Most disease-modifying therapies are safe for long-term use, but they require monitoring. Drugs like natalizumab carry a small risk of PML, so patients are tested for the JC virus before and during treatment. Others, like cladribine, temporarily lower white blood cell counts and need regular blood tests. The bigger risk isn’t the drug-it’s not treating the disease. Untreated MS leads to irreversible nerve damage. Doctors balance risks carefully, choosing treatments based on disease activity, patient age, and lifestyle.