C3PO is a protocol droid often used to translate foreign languages, in Immunology Wars he represents cytokines, which are the chemical messengers that tell the immune system what to do.
Cytokines are proteins that act as chemical messengers in the immune system acting both to activate and regulate the immune response. Cytokines are a large family of diverse proteins, which help to activate, proliferate or differentiate immune cells.
The diversity of cytokines allow for a highly specific, co-ordinated recruitment and activation of immune cells.
Inappropriate production of cytokines has been implicated in a range of diseases, including rheumatoid arthritis, where blocking the action of specific cytokines has been shown to help disease sufferers.