The chemical that gives sunburn its sting has been revealed in rats and humans.
Writing in Science Translational Medicine, Kings College London scientist Steve McMahon and his team gave 10 human volunteers and a group of experimental rats low-levels of sunburn using a UVB lamp. They then took biopsies from the reddened, painful patches of skin and tested them to find out, compared with unburned skin, which genes had been activated.
In both the rats and the humans, the molecule that was most overexpressed was an immune signalling "chemokine" molecule known as CXCL5. Although this was known already to have an inflammatory role, no one had previously linked it to pain or sunburn.
To confirm that CXCL5 could provoke the effects of sunburn, the team then injected it into an unburned patch of skin on another group of rats. The treatment lowered the rats' pain thresholds at the injected site in a similar way to sunburn. They also found that administering an antibody to block CXCL5 prevented sunburn-associated sensitivity.
These results suggest that when a patch of skin is burned, the ensuing damage induces production of CXCL5, among other factors, which recruits immune cells to the site and also sensitises pain-signalling nerve fibres supplying the area. But the benefits of this discovery may not be confined solely to sunburn. CXCL5 might also play a crucial role in sensitising nerves within tissues affected by other inflammatory processes including arthritis. If this is the case then it could prove to be a very valuable target for future analgesics.
Now McMahon is now planning to test tissue samples from patients with a range of painful syndromes to find out to what extent CXCL5 is involved...