These supernatants were used to quantify the presence of IFN-γ, IL-6, IL-10, IL-17, and TGF-β by sandwich ELISA, as previously described ,  and . An ANOVA followed by Tukey’s method was used to evaluate differences GDC-0973 concentration in expression of LTN, Ab titers, and IgG subclass responses; the Mann–Whitney U-test was used to evaluate differences in AFC and CFC responses. The Kaplan–Meier method (GraphPad Prism, GraphPad Software, Inc., San Diego, CA) was applied to obtain the survival fractions following pneumonic Y. pestis challenges in LTN DNA vaccine immunized
mice. Using the Mantel–Haenszel log rank test, the P-value for statistical differences between surviving plague challenges among the vaccinated groups versus those dosed with PBS was discerned at the 95% confidence interval. DNA vaccines for plague were generated using a bicistronic expression plasmid carrying the selleck chemical Libraries molecular adjuvant,
LTN, and under a separate promoter, V-Ag or F1-V fusion protein sequences (Fig. 1A). These are called LTN/V-Ag and LTN/F1-V, respectively. A LTN-based DNA vaccine encoding solely F1-Ag was not found to be as immunogenic as the LTN/F1-V vaccine and, thus, was not used for these studies. To verify the expression of LTN, V-Ag, and F1-V fusion proteins, replicate cultures of 293A cells were transfected with each LTN DNA vaccine, and cell culture supernatants and lysates were collected (Fig. 1B and C). LTN could readily be detected in each of the cell supernatants from the transfected 293A cells when compared to supernatants from DNA plasmids lacking LTN using a LTN-specific ELISA (Fig. 1B). To detect the expression of V-Ag and F1-V fusion proteins, cell lysates were used for immunoblotting. The V-Ag and the F1-V could be detected until using the anti-V-Ag serum (Fig. 1C). The F1-V protein migrated with an
apparent MW of 54 kDa, which represents the expected molecular mass for F1-Ag (17 kDa) plus V-Ag (37 kDa). To evaluate the relative immunogenicity of the LTN DNA vaccines, samples were collected at 6 wks post-primary immunization and subsequently at 2-wk intervals. Past studies with other DNA vaccines show that Ab responses are delayed and peak between 8 and 10 wks post-primary immunization . Ag-specific Ab titers in sera and fecal extracts were measured by ELISA using F1- or V-Ag coated wells (Fig. 2). By 6 wks post-primary immunization to F1- and V-Ag, significant Ab titers were detected in the i.n.- (Fig. 2A and B) and i.m.-immunized groups (Fig. 2C and D), and Ab titers in the i.m.-immunized mice were slightly greater than those in nasally immunized mice on wk 6. While Ab responses to F1-Ag in i.n.-immunized mice steadily increased with time, the anti-F1- or -V-Ag Ab responses in i.m.-immunized mice did not (Fig. 2C and D), nor did the anti-V-Ag Ab responses in nasally immunized mice (Fig. 2B).