Immune function and HPA axis activity in free-ranging rhesus macaques

Area of Science:

• Primate physiology
• Immunology
• Endocrinology

Background:

• The hypothalamic-pituitary-adrenal (HPA) axis and immune system are vital for homeostasis.
• Dysregulation due to stress, particularly in aging individuals, increases disease susceptibility.
• Understanding these systems in free-ranging primates offers insights into stress and aging.

Purpose of the Study:

• To investigate how female age, reproductive state, social rank, and body condition affect cytokine levels and HPA axis activity in rhesus macaques.
• To assess the consistency of individual differences in cytokine and hormone concentrations over time.
• To explore the relationship between immune markers and HPA axis activity.

Main Methods:

• Measured plasma concentrations of interleukin-1 receptor antagonist (IL-1ra), IL-6, and IL-8.
• Assessed plasma and fecal glucocorticoid levels to gauge HPA axis activity.
• Analyzed individual variation and consistency of these measures over successive years.

Main Results:

• Female macaques exhibited increased HPA axis activity during pregnancy and lactation.
• Advancing age was associated with elevated circulating IL-1ra levels.
• Inter-individual differences in IL-1ra and IL-8 were consistent year-to-year.
• Fecal glucocorticoids correlated with plasma cortisol and IL-8 in non-reproductive females.
• Some individuals displayed persistently high cytokine or HPA axis activity, indicating chronic stress or disease.

Conclusions:

• Female age and reproductive state significantly influence HPA axis activity and immune markers.
• Individual variation in cytokine and glucocorticoid levels can be stable traits.
• These findings highlight potential chronic stress or disease in some individuals.
• The study provides a foundation for future research on primate stress and allostatic load.