[A study on the mechanisms of mycobacterial clearance induced by CpG-oligodeoxynucleotides in mice]

To investigate the possible mechanisms of mycobacterial clearance induced by CpG-oligodeoxynucleotides (CpG-ODN) in mice.

Eight-week-old female BALB/c mice were treated with intraperitoneal CpG-ODN (30 microg), while the control mice with normal saline. After 2 weeks, the control mice and the CpG-treated mice were infected with Mycobacterium tuberculosis (1 x 10(6) colony-forming units, H(37)Rv strain) through the tail vein. At 3 weeks, 4 weeks and 6 weeks after mycobacterial infection, the lung and the spleen tissues were examined for histopathological changes. Real time-PCR was performed to measure the messenger RNA (mRNA) of interleukin (IL)-12, IL-18, interferon (IFN)-gamma, IL-4, IL-10 and inducible nitric oxide synthase (iNOS) in the tissues. The homogenates of lungs and spleens were cultured, and the colonies were counted after a 4 weeks incubation period at 37 degrees C.

At 3 weeks and 4 weeks of mycobacterial infection, CpG-ODN-pretreated mice showed less mycobacterial burden in the lungs and the spleens than that in the control mice [(0 +/- 0) x 10(6) CFU/g vs (32 +/- 11) x 10(6) CFU/g, (0 +/- 0) x 10(6) CFU/g vs (10 +/- 4) x 10(6) CFU/g; (26 +/- 4) x 10(6) CFU/g vs (56 +/- 8) x 10(6) CFU/g, (4 +/- 3) x 10(6) CFU/g vs (27 +/- 8) x 10(6) CFU/g]. At 4 weeks of mycobacterial infection, CpG-ODN-pretreated mice displayed increased levels of IL-18 mRNA, IFN-gamma mRNA, iNOS mRNA [(3.6 +/- 0.5, 1.6 +/- 1.1, 0.32 +/- 0.14) vs (0.20 +/- 0.10, 23.17 +/- 4.72, 16.18 +/- 5.09)], and decreased level of IL-12p40 mRNA (5.66 +/- 0.64 vs 14.54 +/- 1.89), but there was no difference in the levels of IL-4 mRNA and IL-10 mRNA in the lungs between CpG-ODN-pretreated mice and the control mice [(0.30 +/- 0.09 vs 0.26 +/- 0.05), (0.28 +/- 0.05 vs 0.29 +/- 0.08)]. CpG-ODN-pretreated mice displayed increased levels of IL-18 mRNA, IFN-gamma mRNA, iNOS mRNA [(5.54 +/- 1.29 vs 0.79 +/- 0.36), (0.52 +/- 0.07 vs 0.21 +/- 0.06), (9.07 +/- 1.81 vs 5.97 +/- 1.44)], and decreased levels of IL-12p40 mRNA, IL-4 mRNA and IL-10 mRNA [(2.10 +/- 0.27 vs 5.07 +/- 0.39), (0.23 +/- 0.10 vs 1.21 +/- 0.26), (0.10 +/- 0.04 vs 0.57 +/- 0.13)] in the spleens as compared with the control mice. In CpG-ODN-pretreated mice, expression level of IFN-gamma mRNA in the lungs at 6 weeks post-infection was higher than that at 4 weeks post-infection (0.95 +/- 0.27 vs 0.32 +/- 0.14).

The activation of Toll-like receptor-9 (TLR-9) with CpG-ODN could enhance murine mycobacterial clearance in vivo. TLR-9-induced anti-mycobacterial activity involves increased expression of IL-18, IFN-gamma, and iNOS but decreased expression of IL-4 and IL-10.