The imidazoquinoline TLR7 agonist negatively affects virus-induced type I and type III IFN induction pathways in primary human plasmacytoid dendritic cells (INM9P.452)

Abstract

Abstract Human pDC recognize Influenza/Flu and HSV through TLR7 and -9, respectively, resulting in production of type I and III IFN and pro-inflammatory cytokines. We observed that TLR7 is constitutively present in the ER and LAMP1-positive late endosomes in pDC, and upon stimulation with Flu, TLR7 co-localization with late endosomes increased. Synthetic small molecule TLR7 ligands from the imidazoquinoline family are being used for anti-viral therapy and as immune adjuvants. We investigated the mechanisms by which 3M003 induces type I and III IFN production in pDCs. We found that 3M003 induced IFNs much more rapidly than Flu or HSV, but at much lower levels. Surprisingly, neither the TLR7 inhibitor IRS661 nor cysteine endolysosomal protease inhibitor Z-FM-FMK affected 3M003 induced IFN production although both effectively inhibited Flu-induced IFN production. In addition, 3M003 inhibited Flu, HSV, HIV and CpGA induced IFN production in pDC when used together with these TLR7/9 agonists. However, 3M003 did not affect uptake by pDC. Interestingly, 3M003 inhibited virus-induced IRF7 nuclear translocation while enhancing its phosphorylation. Taken together, these results suggest that in pDCs, 3M003 utilizes signaling pathways distinct from HSV or Flu resulting in the different levels of IFN production.