• T E Lacourt, J H Houtveen, J J C S Veldhuijzen van Zanten, J A Bosch, M T Drayson, and L J P Van Doornen.
• Department of Clinical and Health Psychology, Utrecht University, Heidelberglaan 1, 3584 CS Utrecht, The Netherlands; Department of Symptom Research, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 1450, Houston, TX 77030, USA. Electronic address: tlacourt@mdanderson.org.
• Brain Behav. Immun. 2015 Feb 1; 44: 32-6.

IntroductionExperimental animal studies provided evidence for a synergistic effect of immunological and psychological stressors on subsequent sickness behaviours. Up to now, little corroborating evidence for such synergy exists for humans, in whom it may provide a mechanism leading to the expression of functional somatic symptoms. The aim of the present study was to determine an interaction between stress(-vulnerability) and an immunological activation on experimental pain sensitivity, i.e., pressure pain threshold and tolerance in healthy humans.MethodsIn healthy female participants (n=25, mean age 22.3 years), negative affectivity (NA) and experienced stress were assessed by questionnaire before receiving a Salmonella typhi vaccine or saline control in a randomized blinded cross-over design. Pressure pain threshold was assessed at the lower back and calves and pain tolerance was assessed at the thumbnail, before and six hours after each injection.ResultsVaccination induced leukocytosis (+100%) and increased serum IL-6 (+670%). NA predicted decreased pain tolerance after vaccination (β=-.57, p=.007), but not after placebo (β=.25, p=.26). Post-hoc analyses also demonstrated an association with administration order.DiscussionNA moderated the effects of inflammation on pain tolerance. This finding is consistent with a synergistic model whereby inflammation may lower the threshold for pain reporting in individuals with increased vulnerability for somatic symptom reporting.Copyright © 2014 Elsevier Inc. All rights reserved.

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