Figure 2.

The CD8 T cell linear differentiation model. Naïve T cells in acute viral infections become activated in lymphoid tissues via canonical and cross presentation of viral antigens by antigen-presenting cells. The activation process ensues with the delivery of signal 1 + 2 and IL2 production. IL2 subsequently diffuses locally and binds IL2 receptor to generate high affinity IL2-R that promotes IL2-R mediating signaling pathway, which is important for proliferation and survival of antigen-specific CD8 T cells. Activated CD8 T cells react with virally infected cells and undergo proliferative expansion and differentiate into terminal T effector cells generating alongside memory precursors that differentiate further into central memory and T effector memory subsets. These memory subsets persist at various sites in vivo.^17–20 The transcription factor expression pattern in CD8 T effector, T cell exhaustion and T cell memory subsets are shown.