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Background: In our study, we investigated whether circulating T follicular helper (Tfh) and the related cytokines are involved in human cystic echinococcosis (CE).Methods: A total of 64 patients with CE and 30 healthy controls were enrolled in this study. Percentages of CCR7(lo)PD-1(hi) cells within CXCR5(+) CD4(+) T cells (circulating Tfh cells) were detected by flow cytometry. Levels of IL-21 and IL-4 in peripheral blood were detected by cytometric bead array. The mRNA expression of IL-21, IL-4, Bcl-6, and Blimp-1 in peripheral blood mononuclear cells (PBMCs) were measured by real-time PCR. Levels of IgG1, IgG2, IgG3, and IgG4 in the patients' sera were measured using enzyme-linked immunosorbent assay.Results: Percentages of circulating Tfh cells were significantly increased in the CE1, CE2, and CE3 groups (p < 0.05). The concentrations of IL-21 and IL-4 in the serum were significantly increased in CE1, CE2, and CE3 groups (p < 0.05). IL-21 was positively correlated with circulating Tfh cells in CE3 group (r = 0.779, p < 0.05). The mRNA levels of IL-21, IL-4, and Bcl-6 were increased in CE1, CE2, and CE3 groups. Levels of IgG1 and IgG4 in patients' sera were increased in CE1, CE2, and CE3 groups. Levels of IgG2 and IgG3 were increased in CE4-5 group. Additionally, after stimulation with hydatid fluid in vitro, the levels of circulating Tfh cells, IL-21 and IL-4 in PBMCs isolated from CE patients were significantly increased (p < 0.05).Conclusions: The levels of circulating Tfh and related cytokines were significantly increased in CE patients, suggesting that they are involved in human CE. [ABSTRACT FROM AUTHOR]