Characterization of T follicular helper cells in allogeneic normal pregnancy and PDL1 blockage-induced abortion

A deeper understanding of the immunological events during pregnancy will provide novel insights into the pathogenesis of pregnancy complications. The fundamental function of T follicular helper (Tfh) cells is to provide cognate help to B cells. Dysregulations of Tfh-cell function and/or development can result in various immunological diseases. However, the role and characteristics of Tfh cells during pregnancy remain unknown. Herein, an allogeneic-normal-pregnant mouse model was used, and we found that the CD4(+) T cells residing at the uterus and placenta (UP) displayed a Tfh-like phenotype; and the UP-derived CD4(+) CXCR5(hi)PD-1(hi) and CD4(+) CXCR5(hi)ICOS(hi) Tfh cells, which showed a memory/activation phenotype, reached their peak at mid-pregnancy. These Tfh cells were located abundantly in the uterus at mid-pregnancy, but greatly increased in the placenta at late-pregnancy. Furthermore, increased foetal resorption by PDL1 blockade correlated with enhanced accumulation of Tfh cells and upregulated expressions of ICOS and PD-1 on these cells. Collectively, our findings are the first to indicate that an adequate and balanced accumulation of Tfh cells during gestation is likely to help maintaining a successful pregnancy, whereas an excessively high level of these cells could lead to abortion.