Why does the immune system fail to clear some virus (and other infections) and allow a state of chronic infection to occur? And when it does, how are immune responses different from a non-infected individual? This article describes the processes involved in T cell exhaustion and considers what can be done to reconstitute the immune system in chronic infections, including HIV.
T cell exhaustion during persistent viral infections. (2015) Virology. 22 Jan. doi: 10.1016/j.virol.2014.12.033
Although robust and highly effective anti-viral T cells contribute to the clearance of many acute infections, viral persistence is associated with the development of functionally inferior, exhausted, T cell responses. Exhaustion develops in a step-wise and progressive manner, ranges in severity, and can culminate in the deletion of the anti-viral T cells. This disarming of the response is consequential as it compromises viral control and potentially serves to dampen immune-mediated damage. Exhausted T cells are unable to elaborate typical anti-viral effector functions. They are characterized by the sustained upregulation of inhibitory receptors and display a gene expression profile that distinguishes them from prototypic effector and memory T cell populations. In this review we discuss the properties of exhausted T cells; the virological and immunological conditions that favor their development; the cellular and molecular signals that sustain the exhausted state; and strategies for preventing and reversing exhaustion to favor viral control.