Human Immune Response and Early Contact With Animals

A team of researchers from fields as diverse as psychology and physiology teamed up recently to study how a person’s immune system might be affected by their contact with animals during childhood (to the age of 15 years old). The investigators compared the degree of immune activation, and the quality of the resolution of this activation, between the two groups in response to social stress. Their results were published in Proceedings of the National Academy of Sciences.

Study Design

Twenty male participants were chosen for each of the study’s 2 groups: (1) those raised in an urban environment without contact with animals and (2) those raised in a rural environment who had contact with farm animals. Participants were screened for factors such as physical and emotional health; exposure to or use of certain drugs or smoking; exercise and body mass index; as well as recent emotional trauma. Urban participants with pets were excluded due to the possibility that pets lower the risk for inflammatory disorders.

RELATED:

• Eczema, Asthma, and the Protective Effect of Dogs
• Does Pet Ownership Impact a Child's Health?

Psychologic and physiologic testing was performed at baseline, as well as at several time points throughout the study. The participants’ physical health was evaluated based on blood pressure, heart rate, plasma and peripheral blood mononuclear cells (PBMCs), alpha-amylase concentrations, and plasma cortisol concentrations. Their mental health was evaluated using a variety of validated methods to evaluate for depression, anxiety, life stresses, as well as childhood trauma and abuse.

The Trier social stress test (TSST) was used to induce stress in the participants by having them perform a simulated job interview, public speaking, and an arithmetic task. Each task was timed and video recorded. In addition, 2 people wore lab coats and were instructed to sit in the room with the participant. These individuals were instructed not to interact with the participants and to maintain a neutral facial expression.

The timing for the metrics of the study were before (—5 min) and after (5, 15, 60, 90, 120 minutes) the TSST. Venous catheters were placed before the study began to facilitate blood sampling. Mental health questionnaires were performed after the final blood sample was taken.

Results

The mental health assessments indicated that there was no difference in these metrics between the urban and rural participants. Anxiety levels, however, were higher in the rural participants.

Basal PBMCs values, the measure of systemic immune activation, did not differ between the 2 groups. However, rural participants’ PBMC values increased only transiently, while the urban groups PBMC values were increased at 5, 60, and 120 minutes. Basal interleukin-6 (IL-6) values were equivalent, but urban participants showed a prolonged increase in IL-6 compared with the rural group. Interestingly, rural group had higher cortisol concentrations.

Conclusions

This study’s findings indicate an increased systemic immune activation and a compromised resolution of inflammation in urban participants raised in the absence of animals versus rural participants raised in the presence of animals. Additionally, the data suggest that rural participants raised in the presence of animals experienced more stress and anxiety from the experimental procedures.

Dr. Ambrose received her DVM from The Ohio State University. She has since worked in small animal clinical practice as well as in the veterinary pharmaceutical industry.