Introduction Bacterial and viral DNA are potent stimuli to immune cells. Synthetic CpG-oligodeoxynucleotides (CpG-ODN) mimic the stimulatory effect of these microbial DNA in activation of immune cells. The activity of a CpG-ODN is determined by its sequence context including its length, the number of CpG motifs, and the spacing, position, and surrounding bases of these motifs. Toll-like receptor 9 (TLR9) is the cellular receptor for these CpG-ODN. Previous studies have shown different ligand recognition profiles of mouse TLR9 and human TLR9. Rabbits are commonly used for production of antibodies. Although CpG-ODN have been shown to be a safety and effective adjuvant in boosting antibody production in rabbits, the interaction between CpG-ODN have not yet investigated. Methods In the present study, we cloned and characterized rabbit TLR9 cDNA. We further established cell-based activations with this rabbit TLR9 cDNA, and cDNAs for mouse and human TLR9 to comparatively investigate activation of these TLR9s. Results The complete open reading frame of rabTLR9 encodes 1028 amino acid residues, which share 70.6% and 75.5% of the identities of mTLR9 and hTLR9, respectively. Similiar to that of human TLR9, rabbit TLR9 is preferentially expressed in immune cells riched tissues, and is localized in intracellular vesicles. While mTLR9 and hTLR9 displayed species-specific recognition of their optimized CpG-ODN, rabbit TLR9 was activated by these CpG-ODN without any preference. Conclusion The results indicated a different ligand recognition profiles of these TLR9 from these species.
