CT is a well-known mucosal adjuvant that stimulates Th2-type responses  and . Elevated IgG1 Abs to F1- and V-Ag were induced, which has been previously deemed important since enhanced IgG1 subclass titers to F1- and V-Ag correlated with protection against plague . Thus, using the described vaccination regimens, mixed Th cell responses were induced supporting the varied IgG subclass responses. Our
results show that immunity to both V- and F1-Ags are required for protection against pneumonic plague evident by the similar levels of protection conferred by mice vaccinated i.m. with LTN/V or LTN/F1-V DNA vaccines plus F1-Ag boosts. These results are consistent with previous observations PD0332991 ic50 that a combination or fusion of these Ags has an additive protective effect when used to immunize mice against plague , ,  and . In addition, others have also reported that the F1- and V-Ag are considered the most effective candidates for vaccines against plague, although vaccination with each protein alone find more is sufficient for protecting mice against plague challenges  and . Indeed, our Ab results in mice immunized with LTN DNA vaccine
expressing V-Ag only or F1-V were consistent with Ab responses obtained in these other studies. Therefore, DNA vaccine expressing a combination of F1- and V-Ag, or as a fusion F1-V-Ag protein, is able to effectively prime for protection against plague. In summary, this is the first description of LTN as a molecular adjuvant that tests DNA vaccines mucosally and parenterally for plague. Using a bicistronic plasmid encoding LTN plus the vaccine encoding V-Ag or F1-V-Ag, we showed effective priming by i.m. delivery of
LTN DNA vaccine followed by booster immunizations with recombinant F1-Ag protein, resulting in protection against pneumonic plague. Th1, Th2, and Th17 cell responses were induced either by mucosal or parenteral vaccination; however, i.m. immunization with Casein kinase 1 the LTN DNA vaccine markedly enhanced Th17 cell immunity when compared to the same vaccines administered nasally. These results suggest LTN can be used as a molecular adjuvant to allow inclusion of a cell-mediated component to enhance protective immunity against plague. This work was supported by NIH-NIAIDR01 AI-56286, NIH/National Center for Research Resources, Centers of Biomedical ExcellenceP20 RR-020185 and, in part, by Montana Agricultural Station and USDA Formula Funds. The challenge studies were partly supported by the Rocky Mountain Regional Center of Excellence for Biodefense and Emerging Infectious Diseases, NIH U54 AI-06537. We thank Ms. Nancy Kommers for her assistance in preparing this manuscript.