Increased frequency of circulating follicular helper T cells in patients with ankylosing spondylitis.

Objective. The relationship between circulating follicular helper T (Tfh) cells and ankylosing spondylitis (AS) remains unclear. The aims of our study were to measure the levels of circulating Tfh cells and several related parameters in patients with AS, and examine the correlation of these factors with disease activity. Methods. We designated CD4 + CXCR5 + ICOS + T cells as circulating Tfh cells. The percentage of circulating Tfh cells was detected using flow cytometry. Plasma IL-21 and immunoglobulin (IgA, IgM, and IgG) levels were quantified using enzyme-linked immunosorbent assay in 60 AS patients and 60 healthy controls (HC). Results. The percentage of circulating Tfh cells was increased in AS patients compared with that in HC. As AS patients were divided into active and inactive groups, the percentage of circulating Tfh cells was significantly increased in active group compared with both inactive group and HC. Plasma IL-21 and immunoglobulin levels were elevated in AS patients, and the differences were significant except IgG. In addition, the percentage of circulating Tfh cells was positively correlated with Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), and plasma IL-21 levels were positively correlated with plasma immunoglobulin levels. But neither circulating Tfh cells nor BASDAI was significantly correlated with plasma IL-21 and immunoglobulin levels in AS patients, with the exception of significant correlation between BASDAI and plasma IgM levels in active AS patients. Conclusion. Our study has shown the increased percentage of circulating Tfh cells correlated with disease activity, and the high plasma IL-21 levels were associated with high plasma immunoglobulin levels in patients with AS, indicating that the circulating Tfh cells may be associated with the development of AS.