Previous studies have suggested that γδT cells play an important role in the pathogenesis of ankylosing spondylitis (AS). In this pilot study, the peripheral blood mononuclear cells (PBMCs) of patients with ankylosing spondylitis (AS) and healthy volunteers were stained and analyzed by flow cytometry to distinguish γδ T cells and its subtypes, and then to report the distribution of γδ T cells and iyts subtypes and their correlation with ankylosing spondylitis. A total of 17 patients with active AS and 10 age- and gendermatched healthy volunteers were enrolled in this study, and their peripheral blood were drawn to collect mononuclear cells (PBMCs). Flow cytometry was used to analyze γδ T cell subpopulations by measuring the surface and intracellular expressions of phenotypic markers. Serum levels of inflammatory and bone turnover markers were measured, and their correlations with subpopulations of γδ T cells were evaluated. In patients with AS, the Vδ2 fractions within γδ T cells and CD3+ T cells decreased significantly, in particular, the proportions of CD27+ Vδ2 T cells, CD86+CD80+ Vδ1 T cells, and IL17A-secreting and TNFα-secreting Vδ1 T cells within the parental cells decreased significantly. γδ T cells/PBMCs, Vδ2 cells/γδ T cells, and Vδ2 cells/CD3+ T cells were negatively correlated with CRP, whereas Vδ1 cells/CD3+ T cells were negatively correlated with ESR. Vδ1 cells/γδ T cells were positively correlated with CRP, γδ T cells/PBMCs were positively correlated with β-CTx, CD69+CD25+ and IL-17A-secreting Vδ1 cells were positively correlated with TP1NP, and CD69+CD25+ Vδ1 and Vδ2 cells were positively correlated with osteocalcin. Decreases in peripheral Vδ2, CD27+ Vδ2, CD86+CD80+ Vδ1, and IL17A or TNFα-secreting Vδ1 T cells are associated with AS. The correlations between γδ T cell subpopulations and CRP and the CD69+CD25+ subpopulation with TP1NP or osteocalcin suggest that an imbalance in peripheral γδ T cell subpopulations contributes to the pathogenesis of AS. [ABSTRACT FROM AUTHOR]