PDYN and infection: Plausible biological mechanisms behind this phenomenon (as well as for reduced post-surgical risk of infection) have been attributed to the leukocyte-rich content which produces: 1) anti-nociceptive molecules (such as b-endorphin, matenkephalin and dynorphin-a) and 2) anti-inflammatory cytokines (such as IL-4, IL-10 and IL-13) (20).