A recent research has pointed out that bacteria can stimulate the pain sensing nerves.
In the case of infected wounds, we cannot just assume that the body's own immune reaction has caused the tenderness of the wound.
A research on mice showed that the immune reaction cannot always be blamed for the extra tenderness of an infected wound. Experiments showed that mice with staph-infected paws reveal symptoms of pain much before immune cells arrived at the site.
Even though immune cells do release pain-causing molecules in their effort to fight microbes, recent research has shown that bacteria can also cause pain.
During their research, scientists grew immune cells and pain-sensing cells together in a dish. While they were on the task of stimulating immune cells by adding bacteria to the mix, they never expected to see an immediate response in the nerve cells. They got the impression that nerve cells could sense the bacteria directly.
It was thought the nerves alert the immune system to the presence of bacteria but during tests researchers saw the opposite of what they expected. Researchers concluded that nerve signals can halt immune responses.