TLR8 is expressed on the surface of endosomes and belong to the same subfamily of leukocyte PRRs. Together, TLR7 and TLR8 mediate recognition of purine-rich ssRNA to elicit an immune response to pathogens that are recognized in the endosome. Naturally derived viral uridine-rich ssRNAs include those of influenza and HIV. TLR7 and TLR8 are also implicated in the recognition of bacterial RNA. TLR8 is expressed in monocytes, macrophages, T cells, and most predominantly in myeloid DCs. TLR7 and TLR8 both signal through MyD88/MAL, including IL-1R–associated kinase-4(IRAK-4) recruitment, to mediate cytokine and IFN production through NF-kB and IFN regulatory factor. In response to proinflammatory cytokine signaling, TLR7 and 8 transcription is induced via NF-kB.
The natural ligand of TLR7 and TLR8 is ssRNA. Small-molecule compounds such as imiquimod and resiquimod also activate both receptors and are the subject of adjuvantation research. Moreover, TLR8 agonist is used for ovarian cancer chemoimmunotherapy. 
 D. J. Dowling, “Recent Advances in the Discovery and Delivery of TLR7/8 Agonists as Vaccine Adjuvants,” ImmunoHorizons, vol. 2, no. 6, pp. 185–197, 2018, doi: 10.4049/immunohorizons.1700063.
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