Synthetic oligodeoxynucleotides containing bacterial CpG motifs trigger an immunomodulatory response that correlates with both the CpG hhhexamers and their flanking regions. In this study, four new phosphodiester backbone CpG ODNs were studied in the contest of the innate immune response to Mycobacterium tuberculosis (MTB) infection. Two out of the four CpG ODNs (CpG2 and CpG3) displayed significant and opposite immunomodulatory effects: CpG2 enhanced MTB containment by human Monocyte-Derived-Macrophages (MDM), while CpG3 promoted an increased pathogen growth, higher ROS and Labile Iron Pool (LIP) levels. Accordingly, for iron homeostasis genes transcription, CpG2 and CpG3 induced, respectively, an iron retention and iron release phenotype.

Moreover, CpG2 induced NLRC4 and TRAF6 gene expression and repressed IKK alpha and TREM1 while CpG3 induced PPBP and IL-36 RN and repressed TRAF6, IL-1B, IL-1R2 and NF-kB2. After MTB infection, CpG2 increased the release of soluble TREM1 protein among many others as compared with fewer innate response-associated proteins induced by CpG3. We suggest that CpG2 helps the containment of MTB infection, by inducing an early tight balance of MDM activation players, including LIP, chemokines, ROS and TREM1 receptors. Oppositely, CpG3 induces in MDM an excessive and unregulated inflammatory response unable to contain MTB infection.