Inhibition of toll like receptor immune responses by microbial pathogens

Toll Like Receptors (TLRs) are pathogen recognition receptors (PRRs) that respond to specific pathogen associated molecular patterns (PAMPs) during microbial invasion. After TLR stimulation a series of cellular responses initiate an inflammatory response and influence specific adaptive immunity that ultimately destroy the pathogen. But the immune response is not always able to control the infection. Pathogens have developed mechanisms to overcome and evade distinct arms of vertebrate immunity. Many of these strategies have been extensively described, but with the recent discovery of TLRs additional means to manipulate the innate immune response are currently being studied. Pathogens generally inhibit TLR mediated immunity by either blocking signals that stimulate further host defense mechanisms or by down-regulating their expression. These inhibitory mechanisms have been mainly elucidated in bacterial systems, whereas in other microorganisms they remain to be identified. Here the strategies that pathogenic microbes use to subvert TLR mediated immune responses are reviewed.