ScienceDaily (2010-12-20) — Researchers may have found a clue to the blues that can come with the flu — depression may be triggered by the same mechanisms that enable the immune system to respond to infection. In a new study, scientists activated the immune system in mice to produce “despair-like” behavior that has similarities to depression in humans.

http://www.sciencedaily.com/releases/2010/12/101220150946.htm