What do positive selection, negative selection, and anergy accomplish? Anatomy- lymphatic system

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.