The imidazoquinoline compounds imiquimod and R-848 are low-molecular-weight immune response modifiers that can induce the synthesis of interferon-α and other cytokines in a variety of cell types. These compounds have potent anti-viral and anti-tumor properties; however, the mechanisms by which they exert their anti-viral activities remain unclear. Here we show that the imidazoquinolines activate immune cells via the Toll-like receptor 7 (TLR7)-MyD88–dependent signaling pathway. In response to the imidazoquinolines, neither MyD88- nor TLR7-deficient mice showed any inflammatory cytokine production by macrophages, proliferation of splenocytes or maturation of dendritic cells. Imidazoquinoline-induced signaling events were also abolished in both MyD88- and TLR7-deficient mice.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $18.75 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Medzhitov, R. & Janeway, C. A. Jr Innate immunity: the virtues of a nonclonal system of recognition. Cell 91, 295–298 (1997).
Aderem, A. & Ulevitch, R. J. Toll-like receptors in the induction of the innate immune response. Nature 406, 782–787 (2000).
Akira, S., Takeda, K. & Kaisho, T. Toll-like receptors: critical proteins linking innate and acquired immunity. Nature Immunol. 2, 675–680 (2001).
Poltorak, A. et al. Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene. Science 282, 2085–2088 (1998).
Hoshino, K. et al. Toll-like receptor 4 (TLR4)-deficient mice are hyporesponsive to lipopolysaccharide: evidence for TLR4 as the Lps gene product. J. Immunol. 162, 3749–3752 (1999).
Hayashi, F. et al. The innate immune response to bacterial flagellin is mediated by Toll-like receptor 5. Nature 410, 1099–1103 (2001).
Hemmi, H. et al. A Toll-like receptor recognizes bacterial DNA. Nature 408, 740–745 (2000).
Yoshimura, A. et al. Recognition of Gram-positive bacterial cell wall components by the innate immune system occurs via Toll-like receptor 2. J. Immunol. 163, 1–5 (1999).
Brightbill, H. D. et al. Host defense mechanisms triggered by microbial lipoproteins through Toll-like receptors. Science 285, 732–736 (1999).
Aliprantis, A. O. et al. Cell activation and apoptosis by bacterial lipoproteins through Toll- like receptor-2. Science 285, 736–739 (1999).
Underhill, D. M. et al. The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens. Nature 401, 811–815 (1999).
Takeuchi, O. et al. Differential roles of TLR2 and TLR4 in recognition of gram-negative and gram-positive bacterial cell wall components. Immunity 11, 443–451 (1999).
Ozinsky, A. et al. The repertoire for pattern recognition of pathogens by the innate immune system is defined by cooperation between Toll-like receptors. Proc. Natl Acad. Sci. USA 97, 13766–13771 (2000).
Takeuchi, O. et al. Discrimination of bacterial lipoproteins by Toll-like receptor 6. Int. Immunol. 13, 933–940 (2001).
Alexopoulou, L., Holt, A. C., Medzhitov, R. & Flavell, R. A. Recognition of double-stranded RNA and activation of NF-κB by Toll-like receptor 3. Nature 413, 732–738 (2001).
Imler, J.-L. & Hoffmann, J. A. Signaling mechanisms in the antimicrobial host defense of Drosophila. Curr. Opin. Microbiol. 3, 16–22 (2000).
Takeuchi, O. et al. Preferentially the R-stereoisomer of the mycoplasmal lipopeptide macrophage-activating lipopeptide-2 activates immune cells through a Toll-like receptor 2- and MyD88-dependent signaling pathway. J. Immunol. 164, 554–557 (2000).
Häcker, H. et al. Immune cell activation by bacterial CpG-DNA through myeloid differential marker 88 and tumor necrosis factor receptor-associated factor (TRAF)6. J. Exp. Med. 192, 595–600 (2000).
Schnare, M., Holt, A. C., Takeda, K., Akira, S. & Medzhitov R. Recognition of CpG DNA is mediated by signaling pathways dependent on the adaptor protein MyD88. Curr. Biol. 10, 1139–1142 (2000).
Kawai, T., Adachi, O., Ogawa, T., Takeda, K. & Akira, S. Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity 11, 115–122 (1999).
Miller, R. L., Gerster, J. F., Owens, M. L., Slade, H. B. & Tomai, M. A. Imiquimod applied topically: a novel immune response modifier and new class of drug. Int. J. Immunopharmacol. 21, 1–14 (1999).
Testerman, T. L. et al. Cytokine induction by the immunomodulators imiquimod and S-27609. J. Leukoc. Biol. 58, 365–372 (1995).
Weeks, C. E. & Gibson, S. J. Induction of interferon and other cytokines by imiquimod and its hydroxylated metabolite R-842 in human blood cells in vitro. J. Interferon Res. 14, 81–85 (1994).
Harrison, C. J., Miller, R. L. & Bernstein, D. I. Posttherapy suppression of genital herpes simplex virus (HSV) recurrences and enhancement of HSV-specific T-cell memory by imiquimod in guinea pigs. Antimicrob. Agents Chemother. 38, 2059–2064 (1994).
Chen, M., Griffith, B. P., Lucia, H. L. & Hsiung, G. D. Efficacy of S26308 against guinea pig cytomegalovirus infection. Antimicrob. Agents Chemother. 32, 678–683 (1988).
Bernstein, D. I., Harrison, C. J., Tomai, M. A. & Miller, R.L. Daily or weekly therapy with resiquimod (R-848) reduces genital recurrences in herpes simplex virus-infected guinea pigs during and after treatment. J. Infect. Dis. 183, 844–849 (2001).
von Krogh, G., Lacey, C. J., Gross, G., Barrasso, R. & Schneider, A. European course on HPV associated pathology: guidelines for primary care physicians for the diagnosis and management of anogenital warts. Sex. Transm. Infect. 76, 162–168 (2000).
Stephenson, J. New therapy promising for genital herpes. J. Am. Med. Assoc. 285, 2182–2183 (2001).
Du, X., Poltorak, A., Wei, Y. & Beutler B. Three novel mammalian Toll-like receptors: gene structure, expression, and evolution. Eur. Cytokine Netw. 11, 362–371 (2000).
Chuang, T.-H. & Ulevitch, R. J. Cloning and characterization of a sub-family of human Toll-like receptors: hTLR7, hTLR8 and hTLR9. Eur. Cytokine Netw. 11, 372–378 (2000).
Wagner, H. Bacterial CpG DNA activates immune cells to signal infectious danger. Adv. Immunol. 73, 329–368 (1999).
Krieg, A. M. Now I know my CpGs. Trends Microbiol. 9, 249–252 (2001).
Krieg, A. M. et al. CpG motifs in bacterial DNA trigger direct B-cell activation. Nature 374, 546–549 (1995).
Yamamoto, T. et al. Synthetic oligonucleotides with certain palindromes stimulate interferon production of human peripheral blood lymphocytes in vitro. Jpn. J. Cancer Res. 85, 775–779 (1994).
Verthelyi, D., Ishii, K. J., Gursel, M., Takeshita, F. & Klinman, D. M. Human peripheral blood cells differentially recognize and respond to two distinct CpG motifs. J. Immunol. 166, 2372–2377 (2001).
Tomai, M. A., Imbertson, L. M., Stanczak, T. L., Tygrett, L. T. & Waldschmidt, T. J. The immune response modifiers imiquimod and R-848 are potent activators of B lymphocytes. Cell. Immunol. 203, 55–62 (2000).
Bishop, G. A. et al. The immune response modifier resiquimod mimics CD40-induced B cell activation. Cell. Immunol. 208, 9–17 (2001).
Megyeri, K. et al. Stimulation of interferon and cytokine gene expression by imiquimod and stimulation by Sendai virus utilize similar signal transduction pathways. Mol. Cell. Biol. 15, 2207–2218 (1995).
Bishop, G. A. et al. Molecular mechanisms of B lymphocyte activation by the immune response modifier R-848. J. Immunol. 165, 5552–5557 (2000).
Bowie, A. et al. A46R and A52R from vaccinia virus are antagonists of host IL-1 and Toll-like receptor signaling. Proc. Natl Acad. Sci. USA 97, 10162–10167 (2000).
Kurt-Jones, E. A. et al. Pattern recognition receptors TLR4 and CD14 mediate response to respiratory syncytial virus. Nature Immunol. 1, 398–401 (2000).
Siegal, F. P. et al. The nature of the principal type 1 interferon-producing cells in human blood. Science 284, 1835–1837 (1999).
Cella, M. et al. Plasmacytoid monocytes migrate to inflamed lymph nodes and produce large amounts of type I interferon. Nature Med. 5, 919–923 (1999).
Liu, Y.-J., Kanzler, H., Soumelis, V. & Gilliet, M. Dendritic cell lineage, plasticity and cross-regulation. Nature Immunol. 2, 585–589 (2001).
Kadowaki, N. et al. Subsets of human dendritic cell precursors express different toll-like receptors and respond to different microbial antigens. J. Exp. Med. 194, 863–869 (2001).
Krug, A. et al. Toll-like receptor expression reveals CpG DNA as a unique microbial stimulus for plasmacytoid dendritic cells which synergizes with CD40 ligand to induce high amounts of IL-12. Eur. J. Immunol. 31, 3026–3037 (2001).
Vasilakos, J. P. et al. Adjuvant activities of immune response modifier R-848: comparison with CpG ODN. Cell. Immunol. 204, 64–74 (2000).
Adachi, O. et al. Targeted disruption of the MyD88 gene results in loss of IL-1- and IL-18-mediated function. Immunity 9, 143–150 (1998).
Chow, J. C., Young, D. W., Golenbock, D. T., Christ, W. J. & Gusovsky, F. Toll-like receptor-4 mediates lipopolysaccharide-induced signal transduction. J. Biol. Chem. 274, 10689–10692 (1999).
We thank Sumitomo Pharmaceuticals for valuable discussions of this work; E. Horita for secretarial assistance; N. Tsuji and N. Iwami for technical assistance; and Hayashibara Biochemical Laboratories for the antibody to IRAK. Supported in part by grants from Special Coordination Founds for Promoting Science and Technology; the Ministry of Education, Culture, Sports, Science and Technology of Japan; and the Japan Society for the Promotion of Science for Young Scientists.
The authors declare no competing financial interests.
About this article
TLR9-Activating CpG-B ODN but Not TLR7 Agonists Triggers Antibody Formation to Factor IX in Muscle Gene Transfer
Human Gene Therapy Methods (2019)
Selected TLR7/8 agonist and type I interferon (IFN-α) cooperatively redefine the microglia transcriptome
Protection induced by Leishmania Major antigens and the imiquimod adjuvant encapsulated on liposomes in experimental cutaneous leishmaniasis
Infection, Genetics and Evolution (2019)
Systemic administration of imiquimod as an adjuvant improves immunogenicity of a tumor-lysate vaccine inducing the rejection of a highly aggressive T-cell lymphoma
Clinical Immunology (2019)
Multifunctional nanoparticles based on a polymeric copper chelator for combination treatment of metastatic breast cancer