The impact of Toll-like receptors on bacterial virulence strategies

The mammalian immune system has evolved in the presence of microbes, both pathogenic and commensal. The consequences of microbial recognition by the host has led to the development of compensatory mechanisms by both the host and microbe to either resist or tolerate the existence of the other. In this review we discuss examples of this co-evolutionary relationship. Because of space considerations and for conceptual clarity, we have focused on detection of bacteria by the Toll-like receptor (TLR) family and highlight examples of bacterial strategies to evade, subvert and in some cases even utilize these receptors.

► Pathogens have evolved multiple mechanisms to evade TLR recognition and signaling.
► Alterations in bacterial surface structures make pathogens less immunostimulatory.
► Pathogens encode virulence factors that directly inhibit TLR signaling pathways.
► Inhibition, escape, or subversion of phagocytosis is a method to avoid TLR detection.
► Some pathogens coopt innate immune signals to initiate virulence.