Associations between immunological and hormonal parameters during healthy pregnancy in mares.

Overview

• This study examined how immune system components and hormone levels interact during different stages of healthy pregnancy in mares (female horses).
• It aimed to understand how these interactions contribute to maintaining pregnancy by analyzing blood samples collected throughout gestation.

Study Objectives

• Evaluate changes in circulating immunological and hormonal parameters across different pregnancy phases.
• Investigate the associations between these immunological and hormonal changes.
• Identify hormonal factors potentially driving immune system modulation during pregnancy.

Methodology

• Sample Collection:
  • Blood samples taken from 8 healthy mares before ovulation and at 30, 90, 150, 210, 240, 270, 300, and 330 days into pregnancy.
• Immunological Analysis:
  • Measured distributions of T cells (CD3+, CD4+, CD8+ subsets) and B cells in peripheral blood.
  • Complete blood counts (CBC) and serum protein profiles were performed.
• Hormonal Analysis:
  • Measured levels of equine chorionic gonadotropin (eCG), progestogens (progesterone and its metabolites), androgens, estrogens, corticosteroids, and thyroid hormones.

Key Findings

• Early Gestation (around 90 days):
  • Significant increase in CD4+ T cell distribution in blood.
  • Concomitant decrease in B cell distribution.
  • These immune changes correlated positively with hormones eCG, progesterone (P4), 5α-dihydroprogesterone (DHP), and estrone sulfate.
  • Inverse correlation between B cell levels and the above hormones.
• Mid-Gestation (around 210 days):
  • Peak in B cell distribution occurred simultaneously with a decline in CD4+ T cells.
  • Increase in serum albumin levels observed.
  • These changes positively correlated with cortisone (a glucocorticoid) and hematocrit levels (which reflect red blood cell concentration).
  • Associations between various androgens and lymphocyte subpopulations were noted.
• Throughout Gestation:
  • Negative correlations found consistently between progesterone, DHP, and estradiol-17β with glucocorticoid metabolites, suggesting hormonal balance affecting immune regulation.
• Late Gestation:
  • Positive correlation between estradiol-17β levels and IgM antibody concentration, indicating immune system activity before parturition.
  • Immune and hormonal parameters showed relative stability during the last 100 days of pregnancy.

Interpretation and Implications

• The study identifies phase-specific patterns where immune cell populations and hormone levels are tightly linked, implying coordinated modulation for pregnancy success.
• Early immunomodulation with increased helper T cells (CD4+) and decreased B cells, influenced by pregnancy hormones, might help tolerate the fetus.
• Later shifts, such as increased B cells and glucocorticoid correlation, may prepare the mare’s immune system for childbirth and neonatal immunity.
• Negative associations between progesterone/estrogens and glucocorticoids suggest a complex hormonal interplay regulating immune steady state.
• The findings contribute to better understanding of reproductive immunology in horses, potentially aiding in managing pregnancy disorders or improving breeding programs.