Fig 2. Rat PBLs from differentially vaccinated rats control intramacrophage Francisella growth in a pattern that reflects vaccine efficacy.

Groups of 6 Fischer 344 rats were vaccinated with LVS, LVS-R, HK-LVS, or PBS (naïve) for a total of 31–37 rats per group, and challenged 5 weeks later i.t. with 10³ CFU F. tularensis. Percent survival after one month is shown with data combined from five independent challenge experiments (Panel A). * indicates significantly greater survival compared to naïve rats or rats vaccinated with LVS-R and HK-LVS; # indicates significantly greater survival compared to naïve rats. There was no significant difference between survival of LVS-R and HK-LVS vaccinated rats. In parallel, BMMΦ from Fischer 344 rats were infected with LVS (Macs alone), and co-cultured with PBLs obtained 5 weeks after vaccination from 3 remaining naïve or vaccinated Fischer 344 rats, as indicated. After two days of co-culture, BMMΦ were lysed to evaluate the recovery of intracellular bacteria. Values shown are the mean numbers of CFU/ml ± SD of viable bacteria for five independent experiments of similar design and outcomes (Panel B). Brackets indicate a significant difference (P < 0.05) between the recoveries of bacteria from macrophages in co-cultures. There was no significant difference between the recoveries of bacteria from co-cultures using LVS-R or HK-LVS-immune PBLs.