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

Equine herpesvirus type 1 (EHV-1) is a major cause of reproductive loss in mares. This cross-sectional field study evaluated serum concentrations of interleukin-2 (IL-2), interleukin-10 (IL-10), interferon-alpha (IFN-α), and interferon-gamma (IFN-γ), together with the IL-10/IL-2 and IFN-γ/IL-10 ratios, in 26 vaccinated pregnant Thoroughbred mares. The analytical cohort comprised healthy, EHV-1 PCR-negative mares (HM, n = 10), EHV-1 PCR-positive mares sampled within 4 h after fetal expulsion at approximately the sixth month of gestation (AM, n = 9), and EHV-1 PCR-positive pregnant mares without clinically relevant signs (WCS, n = 7). EHV-1 DNA was detected using an EHV-1-specific real-time PCR assay, and serum cytokine concentrations were measured using equine-specific ELISA kits. Serum IFN-α, IFN-γ, and IL-2 concentrations were significantly higher in both AM and WCS mares than in HM mares (all Holm-adjusted p < 0.001), whereas no statistically significant differences in these cytokines were observed between the AM and WCS groups. IL-10 concentrations were significantly higher in WCS mares than in both HM and AM mares (both adjusted p < 0.01), and HM and AM mares did not differ significantly. The IL-10/IL-2 ratio was highest in HM mares, intermediate in WCS mares, and lowest in AM mares, with significant differences among all pairwise comparisons (adjusted p ≤ 0.019). Conversely, the IFN-γ/IL-10 ratio was highest in AM mares, intermediate in WCS mares, and lowest in HM mares, again with significant differences among all pairwise comparisons (adjusted p ≤ 0.044). These findings indicate substantial antiviral immune activation in both EHV-1-positive groups, with a comparatively stronger regulatory immune component in WCS mares and a predominantly pro-inflammatory profile in mares sampled after abortion.