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Any of a class of proteins that are located within membranes, often on the cell surface, and are an important part of the innate immune system. Toll-like receptors recognize and bind to pathogens or to fragments resulting from cell damage and then activate biochemical pathways that generate an immune response.
[From Toll, the name of a gene in drosophila fruit flies that when mutated affects embryonic development and the innate immune system, from German toll, amazing, great, cool (in Das is ja toll!, That's really cool!, exclamation of German biologist Christiane Nüsslein-Volhard upon observing in 1985 that mutations in a particular gene caused ventral underdevelopment in drosophila, a discovery that eventually led to the identification of Toll-like receptors), from Middle High German tol, foolish, crazy, good-looking, from Old High German, foolish; akin to Old English dol, dull, from Germanic *dula-, dumbfounded, stupefied.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.