Page 52 - Veterinary Immunology, 10th Edition
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FIG. 2.3 There are many different pattern-recognition receptors
used by the animal body. Most are found on or within cells. Others
are soluble molecules that circulate in the bloodstream.
Toll-Like Receptors
The most significant family of PRRs consists of the toll-like
receptors (TLRs) (Box 2.1). Some TLRs are located on cell surfaces,
where they can bind PAMPs from extracellular invaders such as
bacteria and fungi. Other TLRs are found inside cells, where they
bind PAMPs from intracellular invaders such as viruses.
Box 2.1
Toll-like Receptors
Their name alludes to the original discovery of a protein called
“toll” in fruit flies (Drosophila). This protein was necessary for
proper embryological development. In its absence, the flies
developed abnormally, and the German researchers who first saw
these abnormal flies exclaimed “Toll!” (amazing, or weird!). Toll
protein was subsequently found to be necessary for antifungal
immunity in Drosophila species. When the first pattern-recognition
receptor was identified in mammals, it was found to be similar in
sequence and structure to the Drosophila toll protein, hence “toll-
like receptors.”
TLRs are found on sentinel cells of the innate immune system
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