Mice were maintained at Montana State University Animal Resources Center under pathogen-free conditions in individual ventilated cages under HEPA-filtered barrier conditions and

were fed sterilized food and water ad libitum. For intranasal (i.n.) immunization study, mice at 8–10 wks of age were immunized with each DNA vaccine (80 μg/dose) on wks 0, 1, and 2 with each dose administered over a two-day period. On wks 8 and 9, mice were nasally boosted with 25 μg of recombinant F1-Ag protein [27] plus 2.5 μg of cholera toxin (CT; List Biological Laboratories, Campbell, CA) adjuvant. Before challenge, a final Alpelisib cell line boost of DNA vaccine (100 μg) and F1-Ag protein (25 μg) plus CT adjuvant was given i.n. on wk 12. HKI-272 cell line One group of mice was immunized only with Fl-Ag, as described. For intramuscular (i.m.) immunization study, mice were immunized i.m. with each DNA vaccine on wks 0, 1, and 2. For i.m. immunizations,

100 μg DNA were administered with a needle into the tibialis anterior muscles of the two hind legs, as previously described [28]. On wks 8 and 9, mice were nasally boosted with 25 μg of F1-Ag protein plus 2.5 μg of CT (List Biological Laboratories) adjuvant. Before challenge, a final boost of DNA vaccine (100 μg) i.m. and F1-Ag protein (25 μg) plus CT adjuvant was given i.n. on wk 12. To test the efficacy of the LTN DNA vaccines against pneumonic challenge, immunized mice were transported to Colorado State University, acclimated for at least 7 days, and subjected to nasal challenge with 100 LD50 of Y. pestis Madagascar strain (MG05) >2 wks after the last immunization, as previously described [25] and [27]. All mice care and procedures were in accordance with institutional policies for animal health and well-being. Blood was collected from the saphenous vein. Fresh fecal pellets from individual mice were solubilized in sterile PBS containing 50 μg/ml of soybean trypsin inhibitor (Sigma–Aldrich) by vortexing for 10 min at 4 °C. only After microcentrifugation, supernatants were collected and frozen at −30 °C until assay. Serum and fecal Ab titers were determined

by ELISA. Briefly, recombinant F1- or V-Ag [27] in sterile PBS was coated onto Maxisorp Immunoplate II microtiter plates (Nunc) at 50 μl/well. After overnight incubation at room temperature, wells were blocked with PBS containing 1% BSA for 1 h at 37 °C; individual wells were loaded with serially diluted mouse serum or fecal samples in ELISA buffer (PBS containing 0.5% BSA and 0.5% Tween 20) overnight at 4 °C. Ag-specific Abs were reacted with HRP-conjugated goat anti-mouse IgG, IgA, IgG1, IgG2a, or IgG2b Abs (Southern Biotechnology Associates) for 90 min at 37 °C. The specific reactions were detected with soluble enzyme substrate, 50 μl of ABTS (Moss), and absorbance was measured at 415 nm after 1 h incubation at room temperature using Bio-Tek Instruments ELx808 microtiter plate reader. Endpoint titers were determined to be an absorbance of 0.