The most important function of immune system is to defend the body from different disease causing pathogens. Whenever there is pathology in human body, immune system is activated to protect the vital tissues from harm.
The circumstances of their disappearances are all fascinating, and some, sadly, have never been found. One of the more high-profile missing persons cases of 2012 isn't actually a missing persons case at all. Katherine Jackson was reported as missing in late-July of 2012, by her nephew, Trent Jackson.
Excavations have shown the lost tribe, the Anasazi Indians, who vanished without a trace, lived in the four corners region of Colorado. Many other sites have been found that were ceremonial grounds and burial grounds of many different tribes of the area.