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