TLR9 Inhibition Shortly After Mating Increases Fetal Resorption and Alters B- and T-Cell Costimulatory Phenotypes in an Abortion-Prone Mouse Model

TL;DR

Blocking TLR9 shortly after mating worsens pregnancy outcomes in a mouse model by increasing fetal loss and changing immune cell activity.

Contribution

This study shows that TLR9 inhibition shortly after mating worsens pregnancy outcomes in an abortion-prone mouse model.

Findings

TLR9 inhibition increases fetal resorption in CBA/J females without affecting implantation.

TLR9 antagonist alters B-cell costimulatory markers and reduces Treg and activated T-cell percentages.

Blocking TLR9 signaling exacerbates pregnancy loss and impairs immune cell function in the model.

Abstract

Maternal immune tolerance and controlled inflammatory responses are essential for fetal development and successful pregnancy. Regulatory T cells (Tregs) and B cells with regulatory properties (Bregs) maintain this balance by limiting excessive immune activation through the secretion of anti-inflammatory and tolerogenic cytokines, such as IL-10, TGF-β, and IL-35. Moreover, alterations in the costimulatory potential of antigen-presenting cells (APCs), including B cells, modulate the activation and differentiation of T cells. Toll-like receptors (TLRs), particularly TLR9, influence B-cell antigen presentation and cytokine production, thereby affecting the balance between pro-inflammatory and tolerogenic responses at the maternal–fetal interface. TLR9 overexpression has been observed in several pregnancy-related disorders in both humans and murine models. In this study, we examine whether blocking TLR9 shortly after mating could improve pregnancy outcomes and modulate the regulatory and antigen-presenting functions of B cells, as well as their interactions with T cells. Using an abortion-prone murine model (CBA/J × DBA/2J), we show that intraperitoneal administration of a TLR9 antagonist (ODN 2088) shortly after mating increases embryo resorption in CBA/J females compared to controls without affecting implantation. Flow cytometry analysis further reveals that mice receiving the TLR9 antagonist are characterized by downregulation of CD80 and upregulation of CD86 on B cells, accompanied by reduced expression of CD40L and CD28 on T cells, as well as a lower percentage of Tregs and activated T cells. In conclusion, blocking TLR9 signaling shortly after mating does not improve pregnancy outcomes; conversely, it exacerbates pregnancy loss in the CBA/J × DBA/2J abortion-prone model, while altering the costimulatory phenotype of B and T cells and impairing Treg development during pregnancy.

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