Answer
The following are the signals of T cell activation: first is the binding of the antigen to the to the T cell receptor (TCR).
Work Step by Step
A second signal is costimulation. This can be carried out by about 20 different types of molecules , some of which are cytokines . Some plasma membrane molecules can also act as co-stimulators. These latter molecules act in pairs : one molecule of the pair binds to the T cell, while the other attaches to the APC cell. This enables the two cells to stick together for a period of time.
