|MadSci Network: Immunology|
To answer your medical question. When the body is invaded by a microbe (ie a virus in the flu), the body's immune response (WBCs) becomes activated. The WBCs release chemicals to orchestrate the attack. These chemicals are called cytokines and they are critical in the body's immune defense. For example in HIV disease the virus attacks Helper T Cells which are the "conductors" in the "orchestra" of the immune response. Helper T Cells (AKA CD4 cells) activate and regulate the rest of the immune response via cytokines...if the Helper T Cells are killed the immune system falls apart. Now back to the question. Muscle aches (AKA myalgias) in a viral infection such as the flu are due to the effects of certain cytokines on the muscle which produce pain. Information was attained from a Medical Doctor at University of Connecticut Health Center
Try the links in the MadSci Library for more information on Immunology.