One of the components of the innate immune system that scientists have been studying for the last several years is a family of receptor proteins called the Toll-like receptors (TLR)--a name that comes from their resemblance to a fruit fly receptor called "Toll." In the fly, Toll is important for both embryonic development and for immune functions of the adult organism. In adult fruit flies, the protein is an essential receptor molecule that defends against fungal infections.
In humans, TLRs play a critical role in the immune system because they are the molecules responsible for detecting some of the antigens produced by pathogens. For this reason, Toll-like receptors have been called the eyes of the innate immune system. Normally, when human or mouse cells encounter bacteria or viruses, they recognize proteins, lipids, or other molecular components of these foreign invaders through a family of TLR proteins, and then trigger the immune system's multi-stage biochemical attack on the pathogens.
Humans have at least 10 different TLRs, each of which recognizes a specific subset of antigens. For instance, TLR4 recognizes lipopolysaccharide, a chemical component of the cell walls of certain bacteria like Neisseria meningitides--one of the leading causes of bacterial meningitis. TLR9 recognizes bacterial DNA that contains distinguishing CpG dinucleotides motifs .
TLR3 in Detail
Likewise, TLR3 recognizes double-stranded RNA, which is the form of genetic information carried by many viruses. The structure that Wilson and his colleagues have solved shows how the repeating leucine-rich repeat motifs assem
Source:Scripps Research Institute