Social immunity in insects.

When animals become sick, infected cells and an armada of activated immune cells attempt to eliminate the pathogen from the body. Once infectious particles have breached the body's physical barriers of the skin or gut lining, an initially local response quickly escalates into a systemic response, attracting mobile immune cells to the site of infection. These cells complement the initial, unspecific defense with a more specialized, targeted response. This can also provide long-term immune memory and protection against future infection. The cell-autonomous defenses of the infected cells are thus aided by the actions of recruited immune cells. These specialized cells are the most mobile cells in the body, constantly patrolling through the otherwise static tissue to detect incoming pathogens. Such constant immune surveillance means infections are noticed immediately and can be rapidly cleared from the body. Some immune cells also remove infected cells that have succumbed to infection. All this prevents pathogen replication and spread to healthy tissues. Although this may involve the sacrifice of some somatic tissue, this is typically replaced quickly. Particular care is, however, given to the reproductive organs, which should always remain disease free (immune privilege).