Researchers in Germany have identified a new mechanism of long-lasting pain relief via interleukin-4, says a report in the Journal of Clinical Investigation Insight .
Peripheral nerve inflammation can lead to chronic pain conditions such as fibromyalgia and complex regional pain syndrome. The inflammatory response is mediated by several blood-derived immune cells, which produce cytokines, one of which, IL-4, is already being used to treat pain.
A single injection of IL-4 was injected into an animal model of sciatic pain. When repeated daily, the pain relief lasted for up to eight days in the absence of further injection. This was due to the accumulation of M2 macrophages, which themselves produce opioids. It was found that these cells produced several endogenous opioids such as endorphin, enkephalin and dynorphin, activating opioid receptors at the site of inflammation, reducing pain.
When the M2 macrophages were isolated and transferred to another animal, they also continued to reduce pain.
This research is timely due to the lack of research in pain medicine. The findings are relevant to many immune-mediated diseases, such as arthritis, neurodegenerative diseases and cancer. Interestingly, blood levels of IL-4 are reduced in patients with widespread chronic pain and peripheral neuropathies.
Limitations; the study was only conducted in male mice.