IL-35-Producing Regulatory B Cells Are Positively Correlated with iTr35 Cells in Healthy Pregnancy with Altered Associations Following Pregnancy Loss

Immunological dysregulation may be involved in pregnancy loss. Regulatory T (Treg) and B (Breg) cells, together with interleukin-35 (IL-35), contribute to maternal-fetal tolerance. This study investigated peripheral regulatory cell populations in healthy pregnancy and recurrent spontaneous pregnancy loss (RPL), focusing on the potential relationships between regulatory B and T cells within a coordinated immunoregulatory network associated with immune tolerance during pregnancy. Peripheral blood samples were collected from healthy pregnant women and women following spontaneous miscarriage. Frequencies of Breg subsets, including B10 cells, immature B cells, and plasmablasts, as well as the proportions of cells expressing IL-35, IL-10, PD-L1, and PD-L2, were analyzed. Tregs and the regulatory T-cell subsets iTr35, Tr1, and Th3 were also examined for the expression of IL-35, IL-10, TGF-β, and PD-1. In addition, correlations between Treg and Breg populations were assessed. Miscarriage was associated with significantly reduced frequencies of IL-35+ immature B cells, IL-35+ B10-like cells, IL-35+ plasmablasts, IL-35+ Tregs, and iTr35 cells. A negative correlation was observed between PD-L1-expressing B10-like cells and the frequencies of Treg and Th3 cells. Notably, this study is the first to demonstrate a positive correlation between IL-35-producing Bregs and iTr35 cells in healthy pregnancy. These findings suggest that the observed relationships between peripheral regulatory B- and T-cell populations and IL-35-associated regulatory subsets may be relevant to immune regulation during pregnancy. The iTr35/IL-35+ Breg ratios showed potential discriminatory value between healthy pregnancy and pregnancy loss groups and may warrant further investigation as candidate markers in prospective studies.