Positive selection, negative selection and anergy are ways in which T cells that benefit the body’s immune system are allowed to survive in the body and those that cannot are eliminated. Anergy is the absence of exhibiting any response to antigens and antibodies. When T cells develop in the thymus, those that do not bind with MHC molecules of the body are selected positively and therefore not eliminated. This occurs in the epithelial cells of the Thymus. Negative selection occurs on the surface of other cells. Here T cells which bind strongly to the MHC molecules presenting the body’s own peptides are eliminated.
These two processes leave T cells which can recognize foreign bodies and differentiate them from the body’s own. This is the most important property required by the immune system. In the absence of this either the immune system does not defend the body against foreign bodies or starts to attack the body’s own cells.