CpG oligodeoxyribonucleotides protect mice from Burkholderia pseudomallei but not Francisella tularensis Schu S4 aerosols

Abstract

Studies have shown that CpG oligodeoxyribonucleotides (ODN) protect mice from various bacterial pathogens, including Burkholderia pseudomallei and Francisella tularensis live vaccine strain (LVS), when administered before parenteral challenge. Given the potential to develop CpG ODN as a pre-treatment for multiple bacterial biological warfare agents, we examined survival, histopathology, and cytokine data from CpG ODN-treated C57BL/6 mice to determine whether previously-reported protection extended to aerosolized B. pseudomallei 1026b and highly virulent F. tularensis Schu S4 infections. We found that, although CpG ODN protected mice from aerosolized B. pseudomallei challenges, the immunostimulant failed to benefit the animals exposed to F. tularensis Schu S4 aerosols. Our results, which contrast with earlier F. tularensis LVS studies, highlight potential differences in Francisella species pathogenesis and underscore the need to evaluate immunotherapies against human pathogenic species.

Figure 1

CpG ODN 10103 differently protects mice from aerosolized B. pseudomallei 1026b and F. tularensis Schu S4 challenges. Groups of 8-10 C57BL6/J mice were given saline (bold solid lines) or 150 μg CpG ODN 10103 via intranasal (bold dashed lines) or intraperitoneal (thin solid lines) injection 48 h before or 1 h after being challenged with aerosolize B. pseudomallei 1026b or F. tularensis Schu S4 and observed for 14-28 days. The calculated inhaled bacterial doses are given above each graph. Intraperitoneal and 1 h post-challenge therapies were only administered during the low-dose challenges. Survival curves were compared using log-rank (Mantel-Cox) tests.

Figure 2

CpG ODN 10103 administered intranasally 48 h prior to infection differently effects B. pseudomallei 1026b and F. tularensis Schu S4 pathogenesis in aerosol-challenged mice. At 6 days post infection, mice challenged with B. pseudomallei developed bronchopneumonia and pulmonary abscesses (A: arrowheads) and areas of liver necrosis (B: arrows). By contrast, B. pseudomallei-infected mice pretreated with CpG ODN developed only mild interstitial pneumonia (C) and lymphoplasmacytic hepatitis (D: arrows). F. tularensis-challenged mice exhibited bronchopneumonia and pulmonary abscesses (E, G: arrows) and areas of liver necrosis (F, H: arrows) 6 days after infection regardless of whether or not they received CpG ODN. Cytokine levels in the livers and lungs of saline (red circles)- and CpG ODN (blue squares)-treated mice differed significantly for mice infected with B. pseudomallei but not F. tularensis. Mean cytokine levels for tissues obtained from mice 1, 3, and 6 days after infection are rendered as colored bars. Asterisks indicate statistically significant differences (p < 0.05) between saline- and CpG ODN-treated groups on day 6. Parenthetical values accompanying cytokine labels indicate numbers of independent data points obtained for saline- and CpG ODN-treated mice. Cytokine concentrations below 1 pg/ml fall below the x-axis and are not shown on the graphs. T-tests were used to support qualitative analysis of CBA-generated cytokine data.