Sociality and sickness: have cytokines evolved to serve social functions beyond times of pathogen exposure?

Abstract

During pathogen exposure or some forms of stress, proinflammatory processes induce an array of motivated and behavioral adjustments termed "sickness behaviors". Although withdrawal from social interactions is a commonly observed sickness behavior, the relation between social behavior and sickness is much more complex. Sickness can suppress or stimulate social behavior. Sickness can serve as a social cue. Stressors that are social in nature can induce sickness behaviors, and sickness behavior can be readily suppressed by meaningful social stimuli. The nature, context, and timing of these effects together suggest that cytokine-induced behavior may play a role in mediating social interactions in various non-pathological conditions.

Keywords: Acute phase response; Cytokines; Maternal effect; Neuroimmune; Sickness behavior; Social buffering; Social cue; Social stress.

Conflict of interest statement

Conflict of Interest Statement:

All authors declare that there are no conflicts of interest

Copyright © 2013 Elsevier Inc. All rights reserved.

Figures

Figure 1

Illustration of some of the complexity of relations between sickness and social behavior: (A) Increased proinflammatory cytokine signaling increases sickness, including sickness behavior, but social behavior may be either reduced or increased; (B) Exposure to a sick individual may reduce or have no effect on a partner’s interactions with the sick animal; (C) Social stressors, such as isolation, can be powerful stimulators of increased proinflammatory signaling, and sickness and proinflammatory activity can induce feelings of isolation; (D) meaningful social partners can reduce or “buffer” cytokine signaling and sickness.

Figure 2

Median number of 1-min intervals in which guinea pig pups exhibited sickness behavior during 1 hr (first and last 30-min) of a 2-hr exposure to a novel environment while either alone or with either their mother, a littermate, or an adult male. SIR = semi interquartile range. * p < 0.05 vs other conditions.

Figure 3

A. Median frequency of active behaviors (top row) and median number of 1-min intervals of sickness behaviors (bottom row) shown by young guinea pigs isolated in a novel environment. Each observation period was for 30 min. B. Mean core body temperature of guinea pigs during 12, 15-min intervals of 3-hr periods of isolation in a novel environment. Young guinea pigs were separated on 2 consecutive days and then 10 days after the first. *p < 0.05 vs other two groups.