Figure 2.

Reinvigorating exhausted T cells. (A) Microbial products and cytokines produced in response to microbes activate APCs and stimulate expression of CD80 and CD86. Engagement of CD28 by CD80/CD86 stimulates the expansion and differentiation of naive T cells into effector T cells. (B) Effector T cells eliminate the invading pathogens by secreting cytokines and killing infected cells. (C) Upon resolution of infection, effector T cells give rise to long-lived protective memory T cells. (D) However, during chronic infection, T cells lose function and the ability to proliferate and become functionally exhausted. Exhausted T cells express high levels of PD-1. (E) Blockade of interactions between PD-1 and its ligands can reinvigorate T cells to expand and regain effector functions, including cytokine production and cytolysis.