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Few diseases turn the body’s defenses against it as relentlessly as lupus.

In people with the condition, immune cells mistake the body’s own tissues for invaders. The result is inflammation that can flare again and again, bringing pain, rashes, exhaustion, fever, and, in severe cases, lasting organ damage. Doctors can often keep lupus under control, but they still cannot cure it. Many treatments work by broadly suppressing the immune system, which can leave patients more vulnerable to infections.

Now, a new study points to an unexpected place to look for help: the gut.

Researchers at UT Health San Antonio found that a beneficial bacterium called Faecalibacterium prausnitzii is depleted in people with lupus. When they restored it in lupus-prone mice, signs of immune overactivity fell, gut function improved and kidney damage eased—early evidence that future lupus treatments could eventually come from repairing the microbial ecosystem that helps regulate it.

A Missing Microbe

Lupus often announces itself very painfully, with aching joints, rashes, fevers, and fatigue that just doesn’t go away. In more severe cases, the immune attack reaches the kidneys, where inflammation can scar the filters that clean the blood.

That kidney involvement, called lupus nephritis, is one of the disease’s most serious complications. To prevent it, doctors often use steroids and other immunosuppressive drugs. These medicines can be lifesaving, but they’re blunt tools and can also weaken the body’s natural defences against infection.

That trade-off has pushed scientists to look beyond the immune system itself. Over the past decade, researchers have turned to the gut microbiome for clues to what drives lupus inflammation.

The new study focused on F. prausnitzii, a fiber-digesting gut bacterium that produces butyrate, a compound that helps nourish the gut lining and restrain inflammation. Earlier lupus microbiome studies had suggested a broader loss of beneficial, butyrate-producing bacteria. In the new work, researchers revisited human stool-metagenome data and found F. prausnitzii among the depleted microbes.

The finding gave them a specific question to test: could restoring one depleted bacterium help repair gut function and soften the immune attack?

In lupus-prone mice, it did. Animals given F. prausnitzii showed improved fiber digestion, less breakdown of the mucin layer that protects the gut wall, lower autoimmune activity, and reduced kidney damage. By the time untreated mice showed disease, treated animals had a gut microbiome that looked more like that of healthy mice.

“This is the first time in lupus research that we have identified a bacterium that is depleted and when returned, it helps,” said Laurence Morel, PhD, in a UT Health San Antonio news release.

No Quick Fix Electron microscopy images of F. prausnitzii strains. Credit: Wikimedia Commons

The team used a “multiomics” approach, combining data on microbial genes, gene activity and chemical byproducts to see not just which microbes were present, but what they were doing.

Turns out, the changes didn’t only happen in the gut.

In the colon, treated mice had more immune cells that help keep inflammation under control and fewer signals that stir it up. Their spleens also looked calmer—important because the spleen helps organize immune attacks, including the production of harmful antibodies.

The mice had lower levels of anti-dsDNA antibodies, which target the body’s own DNA and are a classic sign of lupus. Their kidneys also fared better. Lupus can be especially dangerous when it reaches the kidneys, where inflammation can damage the tiny blood filters. In treated mice, researchers saw less kidney injury and fewer immune deposits lodged in those filters.

Morel’s team now wants to study the chemicals made by F. prausnitzii and test how diet may affect the bacterium and lupus markers.

“We want to put all of this together for a mechanistic, stringent study linking different carbohydrates in the diet with health outcomes,” Morel noted.

Of course, this is a study done on mice and lupus in humans can be quite different. Besides. the bacteria were given before lupus symptoms developed.

For now, the takeaway is cautious but exciting. Lupus is usually treated as a disease of the immune system, and it is. But the immune system doesn’t act in isolation. It listens to signals from the gut, from food, and from the microbes that help process that food.

This study suggests that replacing missing gut microbes (or copying the molecules they make) could one day give doctors a more precise way to calm lupus without simply shutting down the immune system.

The study was published in the journal Nature Communications.