Simplified immune synapse in a naïve (CD4 or) CD8 T cell and for an activated CD8+ T cell

Initially, TCRa/b chains recognize a specific peptide presented by an antigen presenting cell via the MHC class 1 molecule, and the CD8 co-receptor binds to stabilize the synapse. CD28 then binds to CD80/86 to lead to downstream activation (bottom), which releases IL-12, IFN-gamma, and meanwhile leads to feedback production of CTLA-4 in cytoplasm, which is rapidly brought to the surface (red). Additional costimulatory receptors (not pictured) on activated T cell/APC synapses include OX40/OX40-ligand, CD40-L/CD40, glucocorticoid-induced tumor necrosis factor (GITR)/GITR-L.