Agonist
vs. Antagonist Peptides
There exists a contiuum of activation of T-cells by
(remember, 5 ITAMs per
TCR can be phosphorylated)
Agonist peptides
peptides, that when bound to MHC, stimulate the full level of activation
Antagonist
peptides atagonize the action of agonist peptides, that is, they are recognized by the TCR, but they actually
inhibit the response of the
T-cell to the agonist MHC:peptide complex
Partial agonists
exist that may, for example, induce a T-cell to secrete cytokines but not to proliferate.
This may allow viral evasion of the host immune system
as it mutates its peptides
from agonist for to antagonist. Also, this may be important in developing lymphocytes where they must react with some
extent to self MHC + self
peptide, but not too efficiently.
Causes of incomplete stimulation: lack of co-receptor
recruitment, lack of
co-receptor interaction, or poor affinity of the TCR resulting in dissolution before signal could be transduced