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

T helper 9 (Th9) cells are a new subset of CD4⁺ T cells characterized by secretion of interleukin-9 (IL-9), which are involved in the pathogenesis of many autoimmune diseases. This study aimed to assess the association between Th9 cells/ IL-9, and rheumatoid arthritis (RA) among Yemeni patients. This case-control study included 200 individuals divided into 100 cases and 100 healthy controls. Peripheral blood samples were obtained from each participant for laboratory analysis. Flow cytometry was utilized to identify T helper subsets by detecting T-helper cell CD markers (CD3, CD4, CD196/CCR6, and CD194/CCR4) as well as intracellular staining for IL-9. CD4 + CCR4 − CCR6 + IL-9 + was operationally defined as a phenotypic marker for Th9. ELISA tests were used to measure anti-CCP, IL-9, RF, and CRP. A statistically significant increase in the percentages of Th9 cells as well as elevated IL-9 concentrations in RA patients compared to the healthy control group ( p < 0.0001). Additionally, there was a significant positive correlation between Th9 cells and IL-9 levels ( r = 0.4272, p < 0.0001). Th9 cells and IL-9 are significantly higher in RA patients than in healthy controls. Further research is warranted to investigate the potential of Th9 cells and IL-9 as biomarkers for diagnosis, prognosis, and therapeutic management of RA patients.