| Title | The discovery of potent immunostimulatory CpG-ODNs widely distributed in bacterial genomes |
|---|---|
| Author | Juan Liu1, Yan Wei2, Yongling Lu2, Yangyuling Li1, Qian Chen2, and Yan Li1,2,3* |
| Address | 1Institute of Modern Biopharmaceuticals, School of Life Sciences, Southwest University, Beibei, Chongqing 400715, P. R. China, 2Medical Research Center, Southwest Hospital, Army Medical University, Chongqing 400038, P. R. China, 3West China Biopharm Research Institute, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P. R. China |
| Bibliography | Journal of Microbiology, 58(2),153-162, 2020, |
| DOI | 10.1007/s12275-020-9289-y |
| Key Words | CpG-ODN, microbial genome, TLR9, innate immunity |
| Abstract | Oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG-ODN) can be specifically recognized by Toll-like receptor 9 (TLR9), provoking innate immune responses. Designed according to this structural feature, many synthetic phosphorothioate CpG-ODNs successfully activate macrophages. However, it is difficult to find potent stimulatory CpG-DNA fragments in microbial genomes. Therefore, whether microbial CpG-DNA substantially contributes to infectious and immune diseases remains controversial. In this study, high-throughput scanning was carried out for thousands of bacterial genomes with bioinformatics tools to comprehensively evaluate the distribution of CpG-DNA fragments. A random sampling test was then performed to verify their immunostimulatory properties by experiments in vitro and in vivo. Natural TLR9-dependent and potent stimulatory CpG-DNA fragments were found in microbial genomes. Interestingly, highly conserved stimulatory CpG-DNA fragments were found in 16S and 23S rDNA sequences with multiple copies, while others were species-specific. Additionally, we found that the reported active motifs were mostly nonstimulatory in natural CpG fragments. This evidence indicates that the previous structural descriptions of functional CpG-ODNs are incomplete. Our study has assessed the distribution of microbial CpG-DNA fragments, and identified natural stimulatory CpG-DNA fragments. These findings provide a deeper understanding of CpG-ODN structures and new evidence for microbial DNA inflammatory function and pathogenicity. |