Innate immune cells may present Toll-like receptors either inside (TLR3 and TLR9, for instance) or outside (TLR4 and TLR5, for instance) the cell, but is there any beneficial reason for this? If so, what is it?
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$\begingroup$ When you say inside of the cell, do you mean in the cytosol or inside the ER, vesicles, endosomes? Remember inside the cell can be many places so please be a little more specific. $\endgroup$– Jeppe NielsenCommented May 1, 2017 at 22:25
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$\begingroup$ By inside, I mean any compartment/region which is located within the cell. $\endgroup$– Mauricio MendesCommented May 2, 2017 at 2:30
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1 Answer
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TLRs are used to identify features that are typical of pathogens. Different TLRs tend to identify different features, so that a wide range of pathogens can be identified. Some of these pathogens may be extracellular (such as some kinds of bacteria that are recognized by TLR4, which is extracellular) and some are intracellular, like viruses (some of which may be identified by TLR7, which is intracellular).
The fact that innate immune cells have these is a little bit of a red herring, because they aren't limited to innate immune cells -- they're widespread among many cell types, and are effective at protecting the specific cell, not just activating innate immune cells.
