Abstract
PROBLEM: Regulatory B-cells (Bregs, CD19(+)CD24(hi)CD38(hi)) are a specialized B-cell subset that suppresses immune responses and potentially contribute to the maintenance of an immune-privileged environment for fetal development during pregnancy. However, little is known about the surrounding immunological environment of Bregs in gestational physiology. The relationship of regulatory T-cells (Tregs, CD4(+)CD25(hi)CD127(lo)FoxP3(+)) to Bregs in coordinating immunoregulation during pregnancy is unknown. We aimed to determine whether peripheral concentrations of Bregs and/or PD-L1-expressing Bregs correlated with Tregs and cytokines during pregnancy. METHOD: Peripheral blood samples were obtained from 29 pregnant women at mean 12 weeks' gestation. Participants were age ≥ 18, self-identified as Latina/Hispanic, and N = 12 primigravid. Peripheral blood mononuclear cells were isolated, stained, and analyzed by flow cytometry to determine percentages of Tregs from CD4(+) T-cells and five Treg subsets defined by immune checkpoint markers, and Bregs and PD-L1(+) Bregs from total B-cells. Levels of 13 cytokines were measured on a Meso Scale Discovery multiplex platform. RESULTS: Bregs positively correlated with pro-inflammatory cytokine interleukin (IL)-6. PD-L1(+) Bregs positively correlated with T-cell suppressive cytokine IL-10. PD-L1(+) Bregs negatively correlated with Tregs and Helios(+), CTLA-4(+), PD-1(+), TIGIT(+), and TIM3(+) Tregs. For primigravida, PD-L1(+) Bregs correlated positively with IL-10 and negatively with Helios(+) and TIGIT(+) Tregs. For multigravida, PD-L1(+) Bregs correlated positively with IL-8 and negatively with Helios(+), CTLA-4(+), PD-1(+), and TIGIT(+) Tregs. CONCLUSIONS: This study provides insight into the immunosuppressive role of Bregs and PD-L1(+) Bregs during human pregnancy. Our results suggest that PD-L1(+) Bregs can employ suppressive mechanisms to limit pro-inflammatory responses in primigravida.