Pain control by immune-derived opioids.

1. The nervous and immune systems communicate with each other by use of cytokines and neuropeptides. 2. Interactions between immune cell-derived opioid peptides and opioid receptors located in peripheral inflamed tissue lead to endogenous analgesia. 3. In addition to their immunological functions, immunocytes are involved in intrinsic pain inhibition. This provides new insights into pain associated with a compromised immune system, as in AIDS or in cancer. 4. The activation of opioid production and release from immune cells may be a novel approach to the development of peripherally acting analgesics. Because such drugs would be targeted towards events in peripheral injured tissue, these analgesics should lack unwanted central side effects typically associated with opioids.