Immune cells linked to rheumatoid arthritis in Yemeni patients

Researchers in Sana’a city, Yemen, report that people with rheumatoid arthritis carry higher levels of a recently recognized immune cell subset, T helper 9 cells, along with elevated concentrations of their signature signaling molecule, interleukin-9, compared with healthy individuals. The case-control study, published in BMC Immunology, enrolled 200 participants: 100 patients with rheumatoid arthritis and 100 healthy controls.

T helper 9 cells are a subset of CD4-positive T lymphocytes defined by their secretion of interleukin-9, a cytokine implicated in inflammatory and autoimmune processes. To identify these cells in the bloodstream, the team drew peripheral blood samples from every participant and used flow cytometry, detecting the surface markers CD3, CD4, CD196/CCR6 and CD194/CCR4, together with intracellular staining for interleukin-9. Cells fitting the pattern CD4-positive, CCR4-negative, CCR6-positive and interleukin-9-positive were operationally counted as T helper 9 cells.

The researchers also measured several blood-based disease markers using enzyme-linked immunosorbent assays: anti-cyclic citrullinated peptide antibodies, rheumatoid factor, C-reactive protein and interleukin-9 itself.

The results showed a statistically significant increase in the percentage of T helper 9 cells among the patients relative to the healthy control group, alongside significantly elevated interleukin-9 concentrations, with p values below 0.0001 for both comparisons. In addition, the study found a significant positive correlation between T helper 9 cell percentages and interleukin-9 levels, with a correlation coefficient of 0.4272 and a p value below 0.0001, meaning that participants with more of these cells tended to have higher circulating amounts of the cytokine.

The authors conclude that T helper 9 cells and interleukin-9 are significantly higher in rheumatoid arthritis patients than in healthy controls, and they call for further research into whether these measurements could serve as biomarkers for diagnosing the disease, assessing its prognosis or guiding therapeutic management.

As with any case-control study, the design shows an association at a single point in time rather than proving that these immune cells drive the disease or that measuring them improves patient outcomes. The comparison involved 100 cases and 100 controls from one city, and the findings describe differences between the groups rather than the course of illness in individual patients over time. The Th9 definition used was operational, based on the specific marker combination the team selected.

Nevertheless, the work adds to a growing body of research on helper T cell subsets in rheumatoid arthritis. Related open-access studies have examined interleukin-9’s role in the joint fluid environment, imbalances among Th17 and regulatory T cells in patient blood, and other cytokine-driven pathways, reflecting sustained scientific interest in how specialized T cell populations contribute to autoimmune joint disease.

Whether that pattern can be developed into a clinically useful test remains a question for future studies.

Subject of Research: The association between T helper 9 cells, interleukin-9 and rheumatoid arthritis in Yemeni patients

Article Title: The association between T helper 9 cells and interleukin-9 with rheumatoid arthritis among Yemeni patients in Sana’a city

Article References: Al-Haimi, R. M., Othman, A. M., & Al-Shamahy, H. A. (2026). The association between T helper 9 cells and interleukin-9 with rheumatoid arthritis among Yemeni patients in Sana’a city. BMC Immunology. https://doi.org/10.1186/s12865-026-00921-w

Image Credits: AI Generated

DOI: 10.1186/s12865-026-00921-w

Keywords: rheumatoid arthritis, T helper 9 cells, interleukin-9, flow cytometry, ELISA, case-control study, Yemen, autoimmunity, biomarkers, BMC Immunology, association, between