Tolerance is a state of immunological unresponsiveness, and an ❌ response of lymphocytes. It exists because lymphocytes have ❌ receptor, as receptors are formed by somatic recombination and sometimes recognise ❌. They must be deleted, or controlled by tolerance.

Peripheral Tolerance is the mechanism for controlling self reactive cells that escaped deletion in their early stages.
• 3 ways this may occur:
1. Ignorance; lymphocytes are ❌ separated from low conc. self-antigen at “immune privileged sites” eg the ❌. The sites also produce ❌.
2. Anergy; antigen specific non-❌, a second signal needed from an ❌ is not there to activate ❌.
3. Suppression; an active process ❌ by a suppressor or regulatory lymphocyte.