Infection-induced proinflammatory cytokines are associated with decreases in positive affect, but not increases in negative affect.

Infection commonly triggers nonspecific psychological and behavioral changes including fatigue and malaise, anhedonia, inability to concentrate, and disturbed sleep that collectively are termed "sickness behaviors". Converging evidence from several lines of research implicate the activities of proinflammatory cytokines as a cause of sickness behaviors. Here we elaborate upon the findings of previous research by examining whether infection-associated elevations in local proinflammatory cytokines are associated with increased negative mood and decreased positive mood. One hundred and eighty-nine healthy adults were experimentally exposed to rhinovirus or influenza virus during a 6-day period of quarantine. Infection, objective signs of illness, nasal IL-1beta, IL-6, and TNF-alpha, and self-reported affect were assessed at baseline and on each of the five post-challenge quarantine days. In the 153 persons who became infected following exposure to the challenge virus, daily production of IL-6, but not IL-1beta or TNF-alpha, was associated with reduced concurrent daily positive affect. One-day lagged analyses showed that daily production of all three cytokines was related to lower positive affect on the next day. All lagged associations were independent of previous-day positive affect and objective signs of illness (mucus production, mucociliary clearance function). There were no associations between cytokines and negative affect. Findings support a causal association between pathogen-induced local cytokine production and changes in positive affect over a 24-h timeline.