Circulating CCR7^loPD-1^hi follicular helper T cells indicate disease activity and glandular inflammation in patients with primary Sjögren's syndrome

Since primary Sjögren's syndrome (pSS) is an autoummune disease of B cell hyperactivity and pathologic autoantibody response, follicular helper T (Tfh) cells and follicular regulatory T (Tfr) cells are suggested to be key players in pSS. We examined subsets of Tfh and Tfr cells from the blood in pSS patients, and whether these subsets represent disease activity, glandular inflammation, or autoantibody responses in pSS. Circulating Tfh and Tfr cells, along with their specific subsets, were identified from the peripheral blood of 18 pSS patients and 14 age-and sex-matched healthy controls (HCs) using flow cytometry analysis. Blood Tfr and Tfh cell ratios were increased in pSS patients compared with HCs. The CCR7^loPD-1^hi subset of circulating Tfh cells was increased in pSS patients with high degree of focal lymphocytic sialadenitis; whereas circulating Tfh cells did not differ between pSS patients and HCs. The frequency of CCR7^loPD-1^hi Tfh cells was significantly correlated with disease activity scores and differentiated B cells. PD-1 expression on blood Tfh and Tfr cells showed positive correlations with IL-21 in pSS. Increasing trend of blood Tfr cells was observed in pSS patients, and blood Tfr cells (particularly Th1 and Th17 subsets) represented hypergammaglobulinemia in pSS. In summary, circulating CCR7^loPD-1^hi Tfh cells indicated disease activity and glandular inflammation in pSS. Circulating Tfr cells, shifted toward Th1 and Th17 subsets, indicated ongoing IgG production in pSS. Subsets of circulating Tfh or Tfr cells could be biomarkers for disease monitoring and patient stratification in pSS.