Differential Serum Cytokine Profiles in Aborting and Subclinically Infected Pregnant Mares with Equine Herpesvirus Type 1.

Overview

• This study investigated differences in immune system signaling proteins, called cytokines, in pregnant mares infected with equine herpesvirus type 1 (EHV-1), comparing those that experienced abortion to those with subclinical infection and healthy controls.

Background

• EHV-1 is a significant viral cause of reproductive failure, including abortion, in pregnant mares.
• The immune response to EHV-1 infection involves cytokines, which are molecules that regulate immune activity, inflammation, and antiviral defense.
• Understanding cytokine profiles in infected mares could clarify why some mares abort while others remain clinically normal despite infection.

Study Design and Methods

• A cross-sectional field study was performed involving 26 pregnant Thoroughbred mares that were vaccinated.
• The mares were divided into three groups:
  • Healthy mares (HM, n=10), EHV-1 PCR-negative.
  • Aborting mares (AM, n=9), EHV-1 PCR-positive and sampled shortly after abortion (~6 months of gestation).
  • Subclinically infected mares (WCS, n=7), EHV-1 PCR-positive but no clinical signs of disease.
• EHV-1 DNA presence was confirmed via a specific PCR assay.
• Serum concentrations of cytokines IL-2, IL-10, IFN-α, and IFN-γ were measured using equine-specific ELISA kits.
• Ratios of IL-10/IL-2 and IFN-γ/IL-10 were also calculated to assess the balance between regulatory and inflammatory responses.

Key Findings

• Both the aborting (AM) and subclinically infected (WCS) mares had significantly higher serum levels of IFN-α, IFN-γ, and IL-2 compared to healthy controls, indicating active antiviral immune responses in infected mares.
• There was no significant difference in these three cytokines between the AM and WCS groups, suggesting similar antiviral activation in infected mares regardless of clinical outcome.
• IL-10, an anti-inflammatory and regulatory cytokine, was significantly elevated in WCS mares compared to both HM and AM groups, indicating a stronger regulatory immune response in subclinical infection.
• The IL-10/IL-2 ratio, reflecting the balance between regulatory (IL-10) and pro-inflammatory (IL-2) signals, was highest in healthy mares, intermediate in WCS mares, and lowest in AM mares, with all pairwise differences significant. This suggests more balanced or regulatory immune activity in healthy and subclinically infected mares, with less regulation in aborting mares.
• The IFN-γ/IL-10 ratio, representing the pro-inflammatory to regulatory balance, was highest in aborting mares, intermediate in subclinical, and lowest in healthy mares, again with significant differences, indicating a stronger pro-inflammatory state associated with abortion.

Interpretation and Implications

• The data indicate that both groups of EHV-1 infected mares have active antiviral immune responses, evidenced by elevated IFN-α, IFN-γ, and IL-2.
• Subclinically infected mares display a comparatively stronger immune regulatory profile with higher IL-10 levels, which might help prevent clinical disease such as abortion.
• Abortive mares exhibit a more pro-inflammatory cytokine profile, with higher IFN-γ/IL-10 ratios, suggesting an immune environment that might contribute to fetal loss.
• These findings improve understanding of immune mechanisms underlying different clinical outcomes in EHV-1 infected pregnant mares and could guide future interventions or therapies aimed at modulating immune responses to prevent abortion.
• Further studies could explore therapeutic strategies that enhance regulatory cytokine responses or limit excessive inflammation to protect pregnancies in EHV-1 endemic settings.