Multiple Sclerosis: How the Immune System Attacks the Nervous System

Multiple sclerosis isn't just a neurological condition-it's an internal betrayal. Your own immune system, designed to protect you, turns against your brain, spinal cord, and optic nerves. This isn't a random glitch. It's a targeted, ongoing attack on the protective coating around your nerve fibers, called myelin. When that coating gets stripped away, signals between your brain and body slow down, misfire, or stop entirely. That’s what causes the numbness, blurred vision, fatigue, and walking problems millions live with every day.

The Body’s Own Soldiers Turn Traitor

Normally, your immune system fights off viruses and bacteria. In multiple sclerosis, something goes wrong. Immune cells that should be attacking invaders instead start seeing myelin as the enemy. These rogue cells-mainly CD4+ T cells and B cells-break through the blood-brain barrier, a tight seal that usually keeps harmful substances out of the central nervous system. Once inside, they trigger inflammation. Macrophages and microglia, the brain’s cleanup crew, rush in and begin chewing up the myelin sheath. This process, called demyelination, leaves nerve fibers exposed and vulnerable.

What’s worse, the damage doesn’t stop there. Without myelin, the underlying nerve fibers-axons-start to degenerate. This is why MS isn’t just about flare-ups; it’s about permanent loss. Studies show that even during quiet periods, the brain continues to lose nerve cells. One study found that 89% of chronic MS lesions show activated microglia, meaning the immune attack never truly sleeps.

Why Does This Happen?

No single cause explains MS. It’s a mix of genes, environment, and bad luck. If you have a close relative with MS, your risk goes up-but most people with MS don’t have a family history. What does show up again and again in research are environmental triggers. Epstein-Barr virus (EBV), the virus that causes mononucleosis, is the strongest known link. People infected with EBV are 32 times more likely to develop MS. Vitamin D deficiency also plays a role. Those with blood levels below 50 nmol/L have a 60% higher risk. Smoking doesn’t just harm your lungs-it doubles the chance of MS worsening over time.

Genes matter too. Over 200 gene variants have been tied to MS risk, mostly involved in immune function. But genes alone don’t cause it. It’s the combination-someone genetically prone to immune overreaction, exposed to EBV, living far from the equator with low sun exposure, and smoking-that creates the perfect storm.

What Happens Inside the Nervous System?

MS isn’t one disease-it’s at least four different patterns of damage, seen under the microscope. Pattern I is mostly T cells and macrophages attacking myelin. Pattern II adds antibodies, suggesting B cells are directly involved. Pattern III shows oligodendrocytes (the cells that make myelin) dying off first, with myelin loss following. Pattern IV is the most devastating: oligodendrocytes are damaged but not destroyed, yet they stop making new myelin entirely.

These patterns explain why treatments work for some but not others. If B cells are the main drivers, drugs like ocrelizumab that target them help. If the problem is the brain’s inability to repair itself, then new therapies aiming to boost remyelination-like clemastine fumarate-are being tested. In one trial, patients showed a 35% improvement in how fast their visual system responded, suggesting myelin was starting to regrow.

Common Symptoms: When Signals Go Silent

What you feel depends on where the damage happens. If the optic nerve is attacked, vision blurs or darkens-sometimes suddenly. This is called optic neuritis. One patient described it as "like a curtain pulling over one eye over 24 hours." If lesions form in the spinal cord, you might feel electric shocks when you bend your neck-a sign called Lhermitte’s phenomenon. Numbness in the arms or legs? That’s myelin damage interrupting touch signals. Walking becomes hard because the brain can’t send clear commands to the legs.

Fatigue hits 80% of people with MS-not the kind you get from staying up late, but a deep, bone-tired exhaustion that doesn’t improve with rest. It’s directly tied to the brain working harder to reroute signals around damaged areas. About 58% report numbness or tingling. Nearly half struggle with walking. These aren’t random symptoms. They’re direct results of the immune system’s destruction of myelin.

Types of MS: Relapsing vs. Progressive

Most people-about 85%-start with relapsing-remitting MS (RRMS). This means they have flare-ups: weeks or months of worsening symptoms, followed by partial or full recovery. These flare-ups are fueled by fresh waves of immune cells entering the CNS. Between attacks, the brain tries to repair itself. But over time, repair fails. The damage adds up.

For 15%, the disease is progressive from day one-primary progressive MS (PPMS). There are no clear relapses. Instead, symptoms slowly get worse. This form is harder to treat because inflammation is less obvious, and the damage is more about nerve degeneration than active immune attacks. Still, ocrelizumab is the first drug proven to slow disability in PPMS, cutting progression by 24%.

Left untreated, half of RRMS patients needed help walking within 15 to 20 years. Today, with modern treatments, that number has dropped to about 30%. That’s the power of stopping the immune system before it does too much damage.

Treatment: Stopping the Attack, Not Just Managing Symptoms

There’s no cure yet. But there are more than 20 FDA-approved drugs to slow MS. They’re called disease-modifying therapies (DMTs). Some, like natalizumab, block immune cells from crossing into the brain. It cuts relapses by 68%, but carries a rare but serious risk: progressive multifocal leukoencephalopathy (PML), a brain infection that can be fatal. That’s why doctors test for the JC virus before prescribing it.

Ocrelizumab targets B cells. It’s used for both RRMS and PPMS. In trials, it reduced relapses by 46% compared to older drugs. Another drug, siponimod, traps immune cells in lymph nodes so they can’t reach the CNS. These aren’t just symptom pills-they’re immune system regulators.

And now, researchers are looking beyond suppression. Can we help the brain repair itself? Trials with clemastine, a common antihistamine, showed promise in restoring some myelin. Other drugs are being tested to wake up oligodendrocytes and get them to rebuild the protective coating. This could change everything.

What’s on the Horizon?

Scientists are now tracking MS through blood tests. A protein called neurofilament light chain (sNfL) leaks into the bloodstream when nerves are damaged. Levels above 15 pg/mL mean active disease-with 89% accuracy. This could one day replace frequent MRIs, letting doctors adjust treatment faster.

Another breakthrough? Neutrophil extracellular traps (NETs). These are sticky webs of DNA and toxins released by immune cells. They’ve been found in 78% of MS relapses and appear to help break down the blood-brain barrier. Blocking NETs might be a new way to prevent attacks.

And then there’s the gut. Emerging research suggests gut bacteria influence MS. People with MS have different microbiomes than healthy people. Clinical trials are testing probiotics and fecal transplants to see if reshaping gut flora can calm the immune system.

Living With MS Today

MS isn’t a death sentence. It’s a lifelong condition, but it’s manageable. With early diagnosis and consistent treatment, many people live full, active lives. Exercise, stress management, and avoiding smoking matter as much as medication. Physical therapy helps maintain mobility. Speech and occupational therapy can address changes in speech or fine motor skills.

Support groups, like those on Reddit’s r/MS, offer real stories-not just clinical facts. People share how they adapt: using voice-to-text when hands get weak, switching to electric bikes when walking becomes exhausting, or learning to rest without guilt when fatigue hits.

The future is brighter than ever. Treatments are getting smarter. Research is moving faster. And the focus is shifting from just stopping attacks to helping the brain heal. That’s the real goal-not just surviving MS, but reclaiming what the disease took away.