Tularemia Vaccination and BALT Figure 2. Survival, morbidity and bacterial dissemination following intranasal challenge. (A) Protection was monitored for 21 days in challenged groups after inoculation with 106 and 105 CFU of LVS. (B) Morbidity associated with bacterial infection was determined by analyzing changes in body weight. The weight regain curve for the LPS-vaccinated group includes the only mouse that survived intranasal challenge (filled grey squares). (C) Bacterial loads in blood of challenged mice. Black dots represent individual mice, while bars represent mean values. ** (P,0.01); *** (P,0.001). doi:10.1371/journal.pone.0011156.g002 clusters with peanut agglutinin-positive (PNA+) germinal center B cells (Figure 6, D and E). The lymphoid clusters detected in lungs from LPS+LVS challenged group and the LPS+rPorB unchallenged group were confirmed to be composed of disorganized B cells and some scattered T cells (Figures 4–6, C and F). Mediastinal lymph nodes were included in the study as positive staining controls (Figures 4–6, B). BALT was also detected in LPS+rPorB vaccinated at 120 days post- infection (data not shown). No viable organisms were detected in the lung, spleen and liver tissue with evident BALT at days 30 and 120 post-infection (data not shown), suggesting the formation of these structures may prevent dissemination of the infection. Morphometric analysis of lymphoid follicles and identification of dendritic cells, antibody producing cells and homeostatic chemokines in lungs To highlight differences in the inflammatory responses induced in the lung tissue of vaccinated/challenged mice and vaccinated/ PLoS ONE | www.plosone.org 4 June 2010 | Volume 5 | Issue 6 | e11156