Regulatory T cells and Toll-like receptors: what is the missing link?

Toll-like receptors (TLRs) are critical sensors for microbial products and are important in initiating both innate and adaptive immune defenses against pathogens. Emerging evidence suggests that TLRs are also expressed by regulatory T cells (Treg) that constitute an important immune suppressive cellular mechanism to curtail TLR hyperactivity to avoid sepsis and autoimmune diseases. This review brings up to date on the expression of functional TLRs on Treg and the functional impact of TLR activation on Treg biology. We argue that the suppressive function of Treg can be augmented or attenuated depending on the nature of TLR stimulations.