Gut bacterium depletion linked to lupus; supplementation shows promise in study

Lupus patients carry a deficit in their gut that their bodies cannot easily repair on their own. Researchers at UT Health San Antonio have identified the missing piece: a bacterium called Faecalibacterium prausnitzii, which is depleted in people with systemic lupus erythematosus, the most common form of the disease. When the team reintroduced the bacterium in animal models, disease markers dropped significantly—a finding published in Nature Communications that marks the first time scientists have pinpointed a specific bacterial absence in lupus and shown that restoring it helps.

Systemic lupus erythematosus is a chronic autoimmune condition affecting roughly 1.5 million Americans. The disease has no cure. The immune system turns on the body's own tissues and organs, triggering inflammation in the joints, skin, brain, heart, lungs, and elsewhere. Patients often spend years moving between doctors, chasing a diagnosis. Current treatment relies on immunosuppressants like steroids, which manage symptoms and slow organ damage but carry their own burden: weight gain, swelling, cardiovascular complications, and a dangerous increase in infection risk. Infection, in fact, is a leading cause of death among lupus patients.

Laurence Morel, a professor in the Department of Microbiology, Immunology and Molecular Genetics at UT San Antonio, and his colleague Yong Ge led the study. "This is the first time in lupus research that we have identified a bacterium that is depleted and when returned, it helps," Morel said. The finding builds on a decade of investigation into the connection between gut microbiota and lupus. Earlier work had shown that the microbiome of lupus patients differs from that of healthy people, and researchers had identified at least three bacterial strains linked to disease progression. But this study goes further: it shows a causal relationship and a path toward intervention.

The mechanism works through a chain of molecular events. Faecalibacterium prausnitzii helps the gut digest dietary fiber, a process that generates butyrate, one of the most common short-chain fatty acids. Butyrate is the primary fuel for cells lining the colon that maintain mucin, a protective barrier between the gut and the rest of the body. When F. prausnitzii is depleted, fiber goes undigested, butyrate production drops, and the barrier weakens. "If you have less bacteria digesting that fiber, you have less short chain fatty acids and a more pro-inflammatory condition," Ge explained. A compromised gut barrier allows inflammatory signals to leak into the bloodstream, fueling the autoimmune response that defines lupus.

When the researchers reintroduced the bacterium in their animal models, the results were striking. Disease markers improved. The kidneys and spleen—organs often damaged by lupus—showed positive changes. The bacterium appeared to work indirectly, nudging the broader microbiome toward healthier patterns of fiber digestion rather than mucin consumption. "We were very excited that a single probiotic strain could do such big things," Ge said. The finding suggests that lupus treatment might one day shift away from broad immunosuppression toward targeted microbial restoration.

But significant hurdles remain before this becomes a clinical reality. Faecalibacterium prausnitzii is not found in common over-the-counter probiotic products. The bacterium is extremely sensitive to oxygen and becomes inactive when exposed to air. It also depletes quickly, meaning patients would need frequent treatment to maintain adequate levels. The exact mechanisms by which the bacterium exerts its protective effects are not yet fully understood.

Morel's team is now pursuing the next phase of investigation. They want to identify which metabolites—the chemical byproducts of bacterial metabolism—are responsible for immune protection or inflammation. If certain metabolites prove beneficial, they could become drugs in their own right. The researchers are also designing studies to examine how diet, the microbiome, and the immune system interact. "We want to put all of this together for a mechanistic, stringent study linking different carbohydrates in the diet with health outcomes," Morel said. The path from animal models to human patients is long, but for the first time, there is a specific target to aim at.