Recent research reveals that there is a link between your immune system and pain. Whether you're recovering from an injury or an infection, or from some sort of distress, your immune system can recognize this and react.
Let's talk about cytokines for a moment. Cytokines are cells which are secreted by other cells of the immune system. They are made by many cells and organs in the body (for example, the spleen) and they have an effect on other cells. Certain types of cytokines encourage inflammation, and other types discourage inflammation. Ideally, cytokines should be balanced in the body. When you are sick with a virus, your body will increase the number of inflammatory cytokines to help you fight the infection.