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Pathogen-associated molecular patterns are small molecular motifs conserved within a class of microbes. They are recognized by toll-like receptors and other pattern recognition receptors in both plants and animals. A vast array of different types of molecules can serve as PAMPs, including glycans and glycoconjugates.
PAMPs activate innate immune responses, protecting the host from infection, by identifying some conserved nonself molecules. Bacterial lipopolysaccharides , endotoxins found on the cell membranes of gram-negative bacteria, are considered to be the prototypical class of PAMPs. LPSs are specifically recognised by TLR4, a recognition receptor of the innate immune system. Other PAMPs include bacterial flagellin , lipoteichoic acid from gram-positive bacteria , peptidoglycan , and nucleic acid variants normally associated with viruses, such as double-stranded RNA , recognized by TLR3 or unmethylated CpG motifs, recognized by TLR9. Although the term "PAMP" is relatively new, the concept that molecules derived from microbes must be detected by receptors from multicellular organisms has been held for many decades, and references to an "endotoxin receptor" are found in much of the older literature. The recognition of PAMPs by the PRRs triggers activation of several signaling cascades in the host immune cells like the stimulation of interferons or other cytokines.