Provoked cytokine response is not associated with distress or induced secondary hyperalgesia in people with...

Psychological distress predicts the onset and worsening of persistent pain, but the mechanisms that underpin this influence are poorly understood. Proinflammatory signalling is a plausible link, given its known connections to distress, pain, and neural upregulation. Sustained distress may prime the inflammatory system to respond more strongly to a phasic noxious challenge, supporting neuroimmune upregulation of central nociceptive signalling and persistent pain. This cross-sectional study tested the hypotheses that in vitro endotoxin-provoked expression of typically proinflammatory cytokines (IL1β, IL6) is a partial mediator between distress and persistent pain, and that it is associated with experimentally induced secondary hyperalgesia, in people with suppressed HIV. Study participants were 99 adults (mean [range] age: 43 [28-64 y/o; 72 females]) with either no pain (n = 54) or persistent pain (n = 45), mostly of black South African ethnicity, low socio-economic status, and with high social support. The results replicated previous reports that distress is associated with persistent pain status and pain severity, and distress was associated with the anatomical extent of pain. However, distress was not associated with provoked cytokine expression, nor was provoked cytokine expression associated with secondary hyperalgesia. The conflict between our findings and prior evidence could reflect the influence of differentially trained immune systems or a more complex relationship arising from diverse psychoneuroimmunological interactions in this sample. This sample's combination of HIV status, African genetic ancestry, financial impoverishment, and rich social interconnectedness is poorly represented in current research and provides an opportunity to deepen insight into psychoneuroimmunological interactions in persistent pain.