The Immune Fulcrum: Regulatory T Cells Tip the Balance Between Pro- and Anti-inflammatory Outcomes upon Infection.

Regulatory T cells (Tregs) are indispensable for immune homeostasis and the prevention of autoimmunity. In the context of infectious diseases, Tregs are multidimensional. Here, we describe how they may potentiate effector responses by assisting in recruitment of T cells into the infection site to resolve infection, facilitate accelerated antigen-specific memory responses, limit pathology, and contribute to disease resolution and healing, to the great benefit of the host. We also explore the villainous functions of Tregs during infection by reviewing several diseases in which the depletion or reduction in Treg frequency allows for better generation of effector memory, and results in acute resolution of infection, as opposed to chronicity or severe long-term outcomes. We describe findings generated using mouse models of infection as well as experiments performed using human cells and tissues. We propose that Tregs represent an immunologic fulcrum, promoting both pathogen clearance and damage control by preventing excessive destruction of infected tissues though unchecked immune responses.