These days it’s about your gut microbiome and what you eat: In a breakthrough study published April 30 in Nature Immunology, researchers have uncovered how certain “good” gut microbes can trigger immune cell transformations that contribute to rheumatoid arthritis—and possibly other autoimmune diseases.
The study, led by scientists at The Ohio State University, traces the journey of an unusual immune cell known as a T follicular helper 17 (TFH17) cell. These hybrid cells originate in the gut but go on to drive inflammation and autoimmunity throughout the body.
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“This is really the first time it’s been shown that T cell plasticity, which typically occurs in the gut, can have this dramatic impact outside the gut with systemic impact on autoimmune disease,” said senior study author Hsin-Jung Joyce Wu, professor of internal medicine in the Division of Rheumatology and Immunology.
Back in 2016, Wu and her team first discovered that commensal bacteria—harmless microbes that usually benefit human health—could provoke the immune system into producing aggressive T cells that promote autoimmune responses. Since then, they’ve been unraveling how this process unfolds.
In the new study, the researchers show that gut-resident T helper 17 (TH17) cells can transform—or “reprogram”—into TFH cells within Peyer’s patches, a type of lymphoid tissue in the small intestine. The twist: these new TFH cells retain key inflammatory traits from their TH17 origin, making them more dangerous.
“These reprogrammed T helper cells adopt characteristics of a new T helper cell type while preserving some of their original traits, making them ‘super powerful and potent’—and if you are dealing with autoimmune disease, that’s bad news,” Wu said.
The team used fate-mapping mouse models to trace how the transformation unfolds. They found that segmented filamentous bacteria—a known gut microbe—accelerated this cell reprogramming. Fluorescent tagging techniques then revealed the cells’ migration from the gut into other parts of the body.
“That’s how we knew they were really traveling,” Wu said. Unlike conventional TFH cells, which typically stay in B cell follicles, these TFH17 cells move around and retain the ability to produce inflammatory proteins like IL-17. They’re also more effective at helping B cells, another immune cell central to rheumatoid arthritis.
“That’s what makes them ultra-pathogenic TFH cells in RA, a systemic disease, because they are very mobile and can potently help B cells,” Wu explained.
To test their pathogenic power, researchers introduced a mix of conventional TFH cells and just 20% TFH17 cells into mice genetically predisposed to develop arthritis. Mice that received the mixed group developed nearly five times more severe joint inflammation than those given only conventional TFH cells.
The implications extend beyond mice. Gene sequencing revealed that the aberrant TFH cells in these models shared significant similarities with TFH cells circulating in the blood of humans with rheumatoid arthritis—including the same gut-derived signature.
“That, to me, was exciting, to find this cross-species signature, which suggests the translational potential of this research,” said Wu.
An estimated 18 million people globally suffer from rheumatoid arthritis, a chronic autoimmune disorder marked by painful inflammation in the joints. While its causes are not fully understood, both genetics and environmental factors—including microbial imbalances in the gut—have been linked to disease risk.
Wu believes the findings may have wider relevance: “We are hoping to improve patients’ health and life. For the future, as TFH17 cells can be found in other types of autoimmune patients, such as lupus patients, if we can determine that these abnormal TFH cells are a potential target not just for RA, but across autoimmune diseases, that would be very useful.”
