Minimal sequence requirements for oligodeoxyribonucleotides activating human TLR9.

Area of Science:

• Immunology
• Molecular Biology
• Nucleic Acid Chemistry

Background:

• Synthetic oligodeoxyribonucleotides (ODNs) containing CpG motifs are known activators of Toll-like receptor 9 (TLR9).
• The activation of TLR9 by ODNs is influenced by their nucleotide sequence, length, and dimerization properties.
• Understanding these sequence properties is crucial for designing effective TLR9 agonists and antagonists.

Purpose of the Study:

• To systematically investigate the sequence motifs of B-class and C-class phosphodiester ODNs that govern TLR9 activation.
• To identify the minimal sequence requirements for activating human TLR9.
• To gain insight into the molecular mechanism of TLR9 ligand recognition.

Main Methods:

• Systematic investigation of sequence motifs in B-class and C-class phosphodiester ODNs.
• Assessing the impact of ODN length and specific nucleotide sequences on TLR9 activation.
• Analyzing the effect of the distance between CpG motifs and flanking sequences on TLR9-mediated B cell activation.

Main Results:

• ODNs shorter than 21 nucleotides and those with adenosine adjacent to the CpG motif showed reduced TLR9 activation.
• The distance between stimulatory CpG motifs modulates B cell activation.
• The minimal ODNs activating human TLR9 contain two CpG motifs separated by 6-10 nucleotides, with a 5'-thymidine and a 3'-poly-thymidine tail.

Conclusions:

• Specific sequence features, including length and the presence/position of CpG motifs, are critical for TLR9 activation.
• The minimal sequence requirements provide a foundation for understanding TLR9 ligand binding.
• Human TLR9 likely possesses two binding sites for CpG motifs with differing affinities, with a stringent site for the 5' CpG motif.