Summary
Innate receptors that detect conserved microbial patterns and trigger inflammatory signalling.
In depth
TLR4 detects bacterial LPS, TLR3 double-stranded RNA, TLR5 flagellin. Signal through MyD88 to NF-kB and interferon regulatory factors. Discovered in Drosophila by Hoffmann and in mammals by Beutler (Nobel 2011).
TLRs at the cell surface detect bacterial parts; endosomal ones detect nucleic acids. Their signalling induces cytokines and costimulatory molecules.
Remember: the innate system is not 'non-specific'; it recognises conserved patterns.
Humans have ten TLRs, found on cell surfaces (TLR1, 2, 4, 5, 6) or in endosomes (TLR3, 7, 8, 9) where they sense nucleic acids. Drosophila Toll was found by Nusslein-Volhard for development, and Hoffmann showed its role in fly immunity, while Beutler found TLR4 as the LPS receptor in mice (2011 Nobel Prize, with Steinman). Signalling through MyD88 or TRIF leads to NF-kB and IRF3.
Excess activation underlies septic shock, and TLR agonists are used as vaccine adjuvants (imiquimod via TLR7; MPL via TLR4 in some vaccines; CpG in hepatitis B vaccine). Polymorphisms affect susceptibility to infection. Plants have similar pattern receptors.
Example: the lipid A of Gram-negative LPS is detected at picomolar levels through TLR4, producing fever.
Frequently asked questions
What is Toll-Like Receptors?
Innate receptors that detect conserved microbial patterns and trigger inflammatory signalling.
Which area of biology covers Toll-Like Receptors, and how advanced is it?
Toll-Like Receptors is one of the 52 topics in Immunology & Disease. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Innate Immunity, Cytokines, mRNA Vaccines.
Can you give an example of Toll-Like Receptors?
TLR agonists are used as vaccine adjuvants.
What should I learn before Toll-Like Receptors?
Work through the Beginner topics in Immunology & Disease first, such as Immune System, Viruses, Innate Immunity, then return to Toll-Like Receptors. Advanced topics assume the Intermediate vocabulary.
What topics are related to Toll-Like Receptors?
The closest topics to Toll-Like Receptors are Innate Immunity, Cytokines, mRNA Vaccines, Blood Groups and Transfusion. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Toll-Like Receptors?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Toll-Like Receptors. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is Toll-Like Receptors different from Innate Immunity?
Toll-Like Receptors: Innate receptors that detect conserved microbial patterns and trigger inflammatory signalling. Innate Immunity: Rapid, non-specific defences such as skin, mucus, phagocytes and inflammation. Read both side by side and note what each one explains.
How should I study Toll-Like Receptors step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Innate Immunity and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.