Scientists solved a 30-year mystery behind Crohn's and colitis: in some people, the body attacks its own inflammation brakes.

Crohn's disease and ulcerative colitis, together called inflammatory bowel disease (IBD), keep the gut painfully inflamed, often for life. Many patients try one medicine after another without finding one that works for long. Part of the reason: doctors usually can't say what's driving the inflammation in each person.

Now scientists in England have found one hidden cause. In some people with IBD, the immune system makes antibodies that switch off the body's own brakes on inflammation. The same discovery finally explains a genetic clue that has puzzled researchers for 30 years (University of Oxford via ScienceDaily, New England Journal of Medicine).

Here's what they found, in plain words.

First: what is IBD?

IBD is when the immune system keeps attacking the lining of the gut, causing pain, diarrhea, bleeding and tiredness. It often starts in the teens or twenties, and it can mean years of strong medicines, hospital stays and sometimes surgery.

It's common. An estimated 2.4 million or more Americans have it (WebMD, on a 2023 study), and the CDC's survey put the number of U.S. adults ever diagnosed at about 3.1 million (CDC). About 500,000 people in the UK live with it (ScienceDaily).

The body's brake pedal: IL-10

Inflammation is your immune system's way of fighting off germs. It's useful, like a car's gas pedal. But every car also needs brakes.

One of the body's most important brakes is a messenger protein called interleukin-10, or IL-10. It tells immune cells, "That's enough, calm down." Doctors have known for years that children born with broken IL-10 genes can get severe IBD very young, because their brakes never worked (ScienceDaily).

What the scientists found

Researchers from the University of Oxford, Newcastle University and Cambridge University Hospitals tested blood from more than 4,900 people with IBD (ScienceDaily, NEJM):

• About 3.5% of them, roughly 1 in 30, had antibodies that block IL-10. Antibodies are normally your body's germ-fighters. These ones latch onto IL-10 and stop it from working. It's like someone cutting your brake line.
• They showed up in both Crohn's disease and ulcerative colitis, and not in more than 1,000 healthy people tested for comparison.
• In people with high levels, the brake was really off: less working IL-10, and immune cells that overreacted with extra inflammation.

So for these patients, the gut stays inflamed not because of some unknown trigger, but because their own immune system disabled the "calm down" signal.

The 30-year mystery

Thirty years ago, Oxford researchers noticed that a particular version of an immune gene, called HLA-DRB1*01:03, was linked to a severe kind of IBD. It's the strongest known genetic risk factor for ulcerative colitis. But nobody could explain why it caused trouble (ScienceDaily, NEJM).

Now there's an answer: people with that gene are far more likely to make the IL-10-blocking antibodies. In the study's main group, the odds of having them were about 50 times higher for people carrying it (NEJM). The gene seems to make it easier for the immune system to mistake IL-10 for an enemy.

"The study now provides clear evidence and contributes the missing link," said Oxford's Holm Uhlig, a senior author (ScienceDaily).

Why it matters

A blood test could come next. If doctors can check for these antibodies, they could spot this group early instead of working through medicine after medicine by trial and error (ScienceDaily).

So could more targeted treatment. Instead of turning down the whole immune system, future treatments might go after the bad antibodies themselves, or the cells that make them. That could mean fewer hospital stays and surgeries for these patients, the researchers say.

"This is the most exciting discovery in a lifetime specialising in IBD," said Oxford's Simon Travis (ScienceDaily).

It also changes how IBD is seen. The findings suggest IBD isn't one disease but several, each with its own cause, which is why one treatment rarely works for everyone.

What it doesn't mean (yet)

• It explains about 1 in 30 cases, not all IBD. Most patients have other causes still being worked out.
• There's no test at your doctor's office yet, and no new treatment has been tested. This discovery is the starting point.
• Don't change your treatment based on this. Anyone with Crohn's or colitis should keep working with their own doctor, and can ask whether research testing might be an option in the future.

The bottom line

For decades, IBD has been treated mostly by its symptoms. This study found a specific, measurable cause for one group of patients: their immune system cuts its own brake line. It also solved a genetic puzzle that has been sitting in the textbooks for 30 years. That's how better, more personal treatments usually start.

Living with a long-term illness

Conditions like IBD can mean a long list of medicines and some hard days. For someone you love who lives alone, our app Support-O gives them a simple morning check-in, so the people they choose know they're okay, plus a clear photo list of every medication. More below.

Sources:

• New England Journal of Medicine: Interleukin-10 Autoantibodies and HLA-DRB1*01:03 in Inflammatory Bowel Disease (2026)
• University of Oxford via ScienceDaily: Scientists solve a 30-year mystery behind inflammatory bowel disease (Oct. 26, 2026)
• CDC: Prevalence of inflammatory bowel disease among U.S. adults
• WebMD: More than 2 million in U.S. have inflammatory bowel disease (2023 study)