About TLR / Toll Like Receptor:
Toll-like receptors, also known as TLRs are a class of proteins that function as part of the innate immune system. These single-pass membrane-spanning receptors are usually expressed on sentinel cells like macrophages and dendritic cells and include the family members TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, TLR9, TLR10, TLR11, TLR12, and TLR13, though the last three are not found in humans.
Toll-like receptors usually play the role of acting as a receptor for molecules that are largely shared by pathogens, which allows the immune system to recognize them. These receptors are often expressed on the membranes of leukocytes including dendritic cells, macrophages, natural killer cells, cells of the adaptive immunity T cells, and B cells, and non-immune cells (epithelial and endothelial cells, and fibroblasts).
Toll Like Receptor Mechanism
The specific mechanisms of the TLR proteins differ from each member of the family and not all of the mechanisms are widely understood. For instance, the mechanism of TLR1 is that it recognizes peptidoglycan and (triacyl) lipopeptides in concert with TLR2 (as a heterodimer), and it mediates the production of cytokines essential for the development of effective immunity.
The interactions of TLRs differ from each example, but they all tend to interact with a respective PAMP or DAMP as a homo- or heterodimer along with a co-receptor or accessory molecule. For instance, TLR1 interacts with TLR2, LPHN1, LPHN2, LPHN3, and DHX36
Toll Like Receptor Structure
Human TLRs are all 700–1100 amino acids long and consist of extracellular, transmembrane, and cytoplasmic domains. The extracellular domain houses the ligand-binding site, and TLRs generally function as homodimers.