Small anti-viral compounds activate immune cells via the TLR7 MyD88–dependent signaling pathway


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 options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The imidazoquinolines activate macrophages in a MyD88-dependent manner.
Figure 2: TLR7-deficient cells respond normally to various immunostimulatory CpG DNAs.
Figure 3: Immune cell activation by the imidazoquinolines is dependent on TLR7.
Figure 4: Activation of intracellular molecules induced by R-848 depends on TLR7.
Figure 5: R-848 induces NF-κB activation through TLR7.
Figure 6: In vivo cytokine responses to R-848 are dependent on TLR7 and MyD88.


  1. 1

    Medzhitov, R. & Janeway, C. A. Jr Innate immunity: the virtues of a nonclonal system of recognition. Cell 91, 295–298 (1997).

    CAS  Article  Google Scholar 

  2. 2

    Aderem, A. & Ulevitch, R. J. Toll-like receptors in the induction of the innate immune response. Nature 406, 782–787 (2000).

    CAS  Article  Google Scholar 

  3. 3

    Akira, S., Takeda, K. & Kaisho, T. Toll-like receptors: critical proteins linking innate and acquired immunity. Nature Immunol. 2, 675–680 (2001).

    CAS  Google Scholar 

  4. 4

    Poltorak, A. et al. Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene. Science 282, 2085–2088 (1998).

    CAS  Article  Google Scholar 

  5. 5

    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).

    CAS  Google Scholar 

  6. 6

    Hayashi, F. et al. The innate immune response to bacterial flagellin is mediated by Toll-like receptor 5. Nature 410, 1099–1103 (2001).

    CAS  Article  Google Scholar 

  7. 7

    Hemmi, H. et al. A Toll-like receptor recognizes bacterial DNA. Nature 408, 740–745 (2000).

    CAS  Article  Google Scholar 

  8. 8

    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).

    CAS  PubMed  Google Scholar 

  9. 9

    Brightbill, H. D. et al. Host defense mechanisms triggered by microbial lipoproteins through Toll-like receptors. Science 285, 732–736 (1999).

    CAS  Article  Google Scholar 

  10. 10

    Aliprantis, A. O. et al. Cell activation and apoptosis by bacterial lipoproteins through Toll- like receptor-2. Science 285, 736–739 (1999).

    CAS  Article  Google Scholar 

  11. 11

    Underhill, D. M. et al. The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens. Nature 401, 811–815 (1999).

    CAS  Article  Google Scholar 

  12. 12

    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).

    CAS  Article  Google Scholar 

  13. 13

    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).

    CAS  Article  Google Scholar 

  14. 14

    Takeuchi, O. et al. Discrimination of bacterial lipoproteins by Toll-like receptor 6. Int. Immunol. 13, 933–940 (2001).

    CAS  Article  Google Scholar 

  15. 15

    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).

    CAS  Article  Google Scholar 

  16. 16

    Imler, J.-L. & Hoffmann, J. A. Signaling mechanisms in the antimicrobial host defense of Drosophila. Curr. Opin. Microbiol. 3, 16–22 (2000).

    CAS  Article  Google Scholar 

  17. 17

    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).

    CAS  Article  Google Scholar 

  18. 18

    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).

    Article  Google Scholar 

  19. 19

    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).

    CAS  Article  Google Scholar 

  20. 20

    Kawai, T., Adachi, O., Ogawa, T., Takeda, K. & Akira, S. Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity 11, 115–122 (1999).

    CAS  Article  Google Scholar 

  21. 21

    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).

    CAS  Article  Google Scholar 

  22. 22

    Testerman, T. L. et al. Cytokine induction by the immunomodulators imiquimod and S-27609. J. Leukoc. Biol. 58, 365–372 (1995).

    CAS  Article  Google Scholar 

  23. 23

    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).

    CAS  Article  Google Scholar 

  24. 24

    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).

    CAS  Article  Google Scholar 

  25. 25

    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).

    CAS  Article  Google Scholar 

  26. 26

    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).

    CAS  Article  Google Scholar 

  27. 27

    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).

    CAS  Article  Google Scholar 

  28. 28

    Stephenson, J. New therapy promising for genital herpes. J. Am. Med. Assoc. 285, 2182–2183 (2001).

    CAS  Article  Google Scholar 

  29. 29

    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).

    CAS  Google Scholar 

  30. 30

    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).

    CAS  PubMed  Google Scholar 

  31. 31

    Wagner, H. Bacterial CpG DNA activates immune cells to signal infectious danger. Adv. Immunol. 73, 329–368 (1999).

    CAS  Article  Google Scholar 

  32. 32

    Krieg, A. M. Now I know my CpGs. Trends Microbiol. 9, 249–252 (2001).

    CAS  Article  Google Scholar 

  33. 33

    Krieg, A. M. et al. CpG motifs in bacterial DNA trigger direct B-cell activation. Nature 374, 546–549 (1995).

    CAS  Article  Google Scholar 

  34. 34

    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).

    CAS  Article  Google Scholar 

  35. 35

    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).

    CAS  Article  Google Scholar 

  36. 36

    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).

    CAS  Article  Google Scholar 

  37. 37

    Bishop, G. A. et al. The immune response modifier resiquimod mimics CD40-induced B cell activation. Cell. Immunol. 208, 9–17 (2001).

    CAS  Article  Google Scholar 

  38. 38

    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).

  39. 39

    Bishop, G. A. et al. Molecular mechanisms of B lymphocyte activation by the immune response modifier R-848. J. Immunol. 165, 5552–5557 (2000).

    CAS  Article  Google Scholar 

  40. 40

    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).

    CAS  Article  Google Scholar 

  41. 41

    Kurt-Jones, E. A. et al. Pattern recognition receptors TLR4 and CD14 mediate response to respiratory syncytial virus. Nature Immunol. 1, 398–401 (2000).

    CAS  Article  Google Scholar 

  42. 42

    Siegal, F. P. et al. The nature of the principal type 1 interferon-producing cells in human blood. Science 284, 1835–1837 (1999).

    CAS  Article  Google Scholar 

  43. 43

    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).

    CAS  Article  Google Scholar 

  44. 44

    Liu, Y.-J., Kanzler, H., Soumelis, V. & Gilliet, M. Dendritic cell lineage, plasticity and cross-regulation. Nature Immunol. 2, 585–589 (2001).

    CAS  Article  Google Scholar 

  45. 45

    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).

    CAS  Article  Google Scholar 

  46. 46

    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).

    CAS  Article  Google Scholar 

  47. 47

    Vasilakos, J. P. et al. Adjuvant activities of immune response modifier R-848: comparison with CpG ODN. Cell. Immunol. 204, 64–74 (2000).

    CAS  Article  Google Scholar 

  48. 48

    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).

    CAS  Article  Google Scholar 

  49. 49

    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).

    CAS  Article  Google Scholar 

Download references


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.

Author information



Corresponding author

Correspondence to Shizuo Akira.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Hemmi, H., Kaisho, T., Takeuchi, O. et al. Small anti-viral compounds activate immune cells via the TLR7 MyD88–dependent signaling pathway. Nat Immunol 3, 196–200 (2002).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing