In MS, pathogenic memory B cells infiltrate the brain and develop into antibody-secreting cells. Chemokine receptors not only define their brain-infiltrating capacity, but also assist in their maturation in germinal centers. How this corresponds to pregnancy, as a naturally occurring modifier of MS, is underexplored. Here, we aimed to study the impact of pregnancy on both ex vivo and in vitro B-cell differentiation in MS. The composition and outgrowth of peripheral B cells were compared between 19 MS pregnant patients and 12 healthy controls during the third trimester of pregnancy (low relapse risk) and postpartum (high relapse risk). Transitional, and not naive mature, B-cell frequencies were found to drop in the third trimester, which was most prominent in patients who experienced a pre-pregnancy relapse. Early after delivery, these frequencies raised again, while memory B -cell frequencies modestly declined. CXCR4 was downregulated and CXCR5, CXCR3 and CCR6 were upregulated on postpartum memory B cells, implying enhanced recruitment into germinal center light zones for interaction with T follicular helper (TFH) cells. Postpartum memory B cells of MS patients expressed higher levels of CCR6 and preferentially developed into plasma cells under TFH-like in vitro conditions. These findings imply that memory B- cell differentiation contributes to postpartum relapse risk in MS.

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 CCR7loPD-1hi 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 CCR7loPD-1hi 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 CCR7loPD-1hi 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.