Recognising your own cells

To defend the body from invasion by foreign material, lymphocytes must be able to distinguish the body's own cells and chemicals from those that are foreign. If they could not do this, the lymphocytes would destroy the organism's own tissue.

It is important to remember that specific lymphocytes are not produced in response to an infection, but that they already exist - all 10 million different types. Given that there are so many different types of…