Regulatory B-Cells Are Associated Negatively With Regulatory T-Cells and Positively With Cytokines in Peripheral Blood of Pregnant Women.

Abstract

Problem: Regulatory B-cells (Bregs, CD19⁺CD24^hiCD38^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^hiCD127^loFoxP3⁺) 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.