It is accepted that inflammatory mediators released from leukocytes contribute to the
generation of pain. However, it is less well known that immune cells also produce mediators
that can effectively counteract pain. These include anti-inflammatory cytokines and opioid
peptides. This article concentrates on recent evidence that interactions between leukocyte-
derived opioid peptides and their receptors on peripheral sensory neurons can result in
potent, clinically relevant inhibition of pathological pain. Inflammation of peripheral tissues …