Negative regulation of the type I interferon signaling pathway by synthetic Toll-like receptor 7 ligands.

Ten Toll-like receptor (TLR) family members have been reported in humans. Here, the endoplasmatic receptors TLR9, TLR8, TLR7, and TLR3 respond to nucleic acids and derivatives or to small molecules (TLR7 and 8). Another cytoplasmic RNA receptor, retinoic acid inducible gene I (RIG-I), is stimulated by 5' triphosphate double-stranded RNA.

Impact of delivery systems on siRNA immune activation and RNA interference.

Small interfering RNAs (siRNAs) induce robust degradation of homologous mRNAs. Highly specific silencing of target genes makes siRNA an interesting tool in drug development. However, several non-specific effects complicate the use of RNA interference (RNAi).

Immunostimulatory potential of silencing RNAs can be mediated by a non-uridine-rich toll-like receptor 7 motif.

Microbial infections trigger a multiplicity of responses in the host via innate immune sensors, including the Toll-like receptors (TLRs). TLR7 and TLR8, located in endosomes, detect pathogen-derived RNA, which can be mimicked by synthetic single-stranded oligoribonucleotides (ORNs). Detailed analysis of the immunostimulatory properties of numerous silencing RNAs (siRNAs) revealed that almost all tested siRNAs with a phosphodiester backbone actively stimulated cytokine production in human peripheral blood immune cells, but not all of them did contain previously described guanosine/uridine TLR7 or adenosine/uridine TLR8 motifs.

Structure-activity relationship studies on the immune stimulatory effects of base-modified CpG toll-like receptor 9 agonists.

Synthetic oligodeoxynucleotides containing unmethylated deoxycytidylyl-deoxyguanosine dinucleotide (CpG) motifs are able to stimulate potent immune responses through a signaling pathway involving Toll-like receptor 9 (TLR9). We have investigated the structure-activity relationship (SAR) of base-modified CpG oligonucleotides with TLR9 by measuring TLR9 activation by 20-mer oligonucleotides having just a single human recognition motif (5'-GTCGTT-3') in functional cell-based TLR9 assays. Substitution of guanine by hypoxanthine and 6-thioguanine resulted in activity similar to the unmodified parent molecule, whereas purine, 2-aminopurine, 2,6-diaminopurine, and 8-oxo-7,8-dihydroguanine substitution resulted in approximately 40-60 % reduction in activity, and 7-deazaguanine substitution led to the strongest (80 %) reduction in TLR9 stimulation.

Modulating responsiveness of human TLR7 and 8 to small molecule ligands with T-rich phosphorothiate oligodeoxynucleotides.

Toll-like receptors (TLR) 7 and 8 are closely related members of the TLR family of pathogen-associated molecular pattern recognition receptors and have an important function in activation of innate immune responses upon viral infection. TLR7 can be activated selectively by the guanosine analogue loxoribine, whereas the imidazoquinoline derivative Resiquimod (R-848) activates both TLR7 and TLR8. We demonstrate that co-incubation of R-848 with thymidine homopolymer oligodeoxynucleotides (ODN) significantly increased activity of R-848 on TLR8-expressing HEK 293 cells, but abolished TLR7-mediated signaling.

CpG oligodeoxynucleotides stimulate IFN-gamma-inducible protein-10 production in human B cells.

Several classes of CpG oligodeoxynucleotides (ODNs) with different immune stimulatory profiles were recently identified: the A-, B- and C-classes. In this study, we investigated the CpG-dependent stimulation of IFN-gamma-inducible protein 10 (IP-10 or CXCL10) in different human immune cell types. CpG ODNs induced IP-10 in monocytes, pDCs and in B cells.

C-Class CpG ODN: sequence requirements and characterization of immunostimulatory activities on mRNA level.

Synthetic oligodeoxynucleotides (ODN) containing unmethylated deoxycytosine-deoxyguanosine (CpG) motifs are very potent inducers of the innate immune system, mimicking the effects of bacterial DNA. CpG ODN are recognized by Toll-like receptor 9 (TLR9). Three classes of TLR9 agonists have been described: B-Class CpG ODN that induce strong B- and NK-cell activation and A-Class ODN that induce very high levels of IFN-alpha by plasmacytoid dendritic cells.

Impact of modifications of heterocyclic bases in CpG dinucleotides on their immune-modulatory activity.

Synthetic phosphorothioate oligodeoxynucleotides (ODN) bearing unmethylated CpG motifs can mimic the immune-stimulatory effects of bacterial DNA and are recognized by Toll-like receptor 9 (TLR9). Past studies have demonstrated that nucleotide modifications at positions at or near the CpG dinucleotides can severely affect immune modulation. However, the effect of nucleotide modifications to stimulate human leukocytes and the mechanism by which chemically modified CpG ODN induce this stimulation are not well understood.