Seminal plasma exposure modulates peripheral T cell-associated transcription during early pregnancy in the mare.

Overview

• This study investigates how exposure to seminal plasma affects immune system signals related to T cells during early pregnancy in mares (female horses).
• The research specifically looks at changes in gene expression related to regulatory T cells (which promote immune tolerance) and pro-inflammatory T helper 1 cells, and how these changes relate to pregnancy success and breeding methods.

Background

• Successful pregnancy requires the mother’s immune system to tolerate the presence of paternal antigens delivered during insemination.
• Regulatory T cells (Tregs) help create immune tolerance, while pro-inflammatory T helper 1 (Th1) cells can potentially negatively impact pregnancy.
• In several species, seminal plasma (the fluid part of semen without sperm) has been shown to influence maternal immune adjustment, but its role in mares is not well understood.
• In horse breeding practices, the amount of seminal plasma is often reduced or removed, possibly affecting immune responses.

Objectives

• Characterize how the expression of genes associated with Treg and Th1 cells changes over time in early pregnancy in mares.
• Determine the relationship between these immune gene expressions and pregnancy outcomes.
• Assess how exposure to seminal plasma at insemination affects the development and gene expression of T cells.

Methods

• Peripheral blood mononuclear cells (PBMCs) were collected from mares at multiple time points: before insemination and during early pregnancy.
• Quantitative real-time PCR (qRT-PCR) was used to measure relative expression levels of key immune-related genes:
• Treg-associated genes: FoxP3, CD25, and TGF-β.
• Th1-associated genes: TBX21 and IFN-γ.
• Statistical analyses considered factors such as the length of gestation, pregnancy diagnosis (pregnant or not), and breeding method (including seminal plasma exposure).

Key Findings

• FoxP3 expression, a marker for regulatory T cells, increased over time in pregnant mares, indicating a rise in immune regulatory signaling during early pregnancy (statistically significant with p=0.04).
• Other gene transcripts did not show significant temporal changes overall.
• Pregnancy outcome was linked to IFN-γ expression (a pro-inflammatory marker), with higher IFN-γ levels observed in mares that failed to become pregnant, especially before breeding and around day 7 post-ovulation (p=0.05).
• Exposure to seminal plasma influenced expression of CD25 (a Treg marker), with significantly higher levels at day 14 post-insemination in mares bred with fresh semen containing seminal plasma (p=0.04).
• There was a trend (though not statistically definitive, p=0.06) for increased TGF-β expression associated with seminal plasma exposure.

Interpretation

• The increase in FoxP3 suggests that regulatory T cell activity ramps up during early pregnancy, supporting the development of maternal immune tolerance to the fetus.
• Higher IFN-γ in non-pregnant mares suggests that an elevated pro-inflammatory environment could inhibit pregnancy establishment.
• Seminal plasma exposure appears to promote Treg-associated signals (CD25 and possibly TGF-β), which may be important for fostering immune tolerance at the maternal-fetal interface.
• Since routine horse breeding often involves reducing seminal plasma, this practice might inadvertently diminish beneficial immune modulation necessary for pregnancy success.

Implications

• Understanding how seminal plasma contributes to immune modulation could improve breeding outcomes by optimizing insemination protocols.
• Maintaining seminal plasma during breeding could enhance maternal immune tolerance and potentially increase pregnancy rates in mares.
• This research provides insight into the immunological mechanisms behind early pregnancy success and failure related to semen handling practices in horse breeding.