Psychosocial Stress and Immunity-What Can We Learn From Pig Studies?

Ulrike Gimsa,Ellen Kanitz,Margret Tuchscherer

doi:10.3389/fnbeh.2018.00064

Abstract

Psychosocial stress may impair immune functions and provoke the development of pathologies. The underlying communication between the brain and the immune system is being studied predominantly in rodents. However, pigs offer several advantages as preclinical models for humans because pigs are more similar to humans than rodents in many anatomical and physiological characteristics. Unlike in rodents, the main stress-induced glucocorticoid in humans and pigs is cortisol with a similar circadian rhythm. In this study, we summarize data on short-term and long-term effects of social stress in pigs for their immunity and neuroendocrine regulation with consequences for their health and well-being. As typical social stressors, regrouping, crowding, social isolation, and maternal deprivation have been studied. Psychosocial stress in pigs may affect various reactions of innate and adaptive immunity, such as leukocyte distribution, cytokine secretion, lymphocyte proliferation, and antibody production as well as immune responses to viral infection or vaccination. Furthermore, social stress may induce or promote gastrointestinal diseases through dysregulation of inflammatory processes. In piglets, psychosocial stress may also result in glucocorticoid resistance of lymphocytes, which has been discussed as a cause of allergic asthma in humans. Stress-related neuroendocrine alterations in the cortico-limbic structures, such as the prefrontal cortex, amygdala, hippocampus and hypothalamus, have been demonstrated in pigs at different ages. Based on these data, we propose using pigs as models for psychosocial stress in humans to study the mechanisms of brain-to-immune and immune-to-brain communication from the systemic level down to the cellular and subcellular levels.

Highlights

There is growing evidence that psychosocial stress may affect the immune system in humans
Psychosocial stress in pigs has often been studied in experimental setups that are similar to common practices in animal husbandry
These stressors usually do not have equivalents in human life, they may reflect the moderate intensity of psychosocial stress in the human society better than some of the rodent stress models

Summary

INTRODUCTION

There is growing evidence that psychosocial stress may affect the immune system in humans. Repeated regrouping of pregnant sows represents a social stressor that may affect stress regulation and the immune systems of their offspring (Couret et al, 2009a,b; Otten et al, 2010; Sandercock et al, 2011), with stress in late pregnancy apparently being more relevant for the immune functions of offspring than stress in early pregnancy (Otten et al, 2015) Another important stressor in pigs is the weaning process, which besides environmental and nutritional changes has a strong psychosocial component. To explicitly study psychosocial stress, a repeated daily isolation procedure of piglets was performed This isolation stressor diminished TNF increases after LPS challenge and enhanced signs of sickness, which resulted in a stronger relationship between duration of sickness symptoms and physiological measures (Tuchscherer et al, 2004, 2006).

LIMITATIONS

CONCLUSIONS AND FUTURE DIRECTIONS