Fig. 2: Serum from CLH001 and PBK001 immunized mice enhances bacterial killing and promotes opsonic macrophage activity but is insufficient to protect mice from Bpm infection.
The immune serum from mice (n = 10) receiving PBS, CLH001, and PBK001 were collected two weeks after the 2nd boost. a The serum bacterial killing assay was performed by incubating Bpm K96243 cells (1 × 106 CFU) with 20% heat-inactivated (HI) pooled serum from non-vaccinated and vaccinated mice with and without complement. CFU/ml was determined after 4 h of incubation. b Opsonophagocytosis assay was performed by incubating the HI pooled serum with Bpm K96243 (5 × 105 CFU) for 1 h. Opsonized bacteria were added to RAW 264.7 cells monolayers (5 × 105 cells/well). Uptake was quantitated at 3 h post infection. Values of serum bacterial killing and opsonophagocytosis assay are represented as mean ± SEM from three individual assays conducted in triplicate. c Total IgG of post-vaccine sera used for passive transfer was quantitated using ELISA. Data are represented as mean ± SEM of triplicate assay. d Passive transfer of immunized and non-immunized mice was evaluated by i.p. injection of pooled serum (500 μl) to naïve C57BL/6 mice (n = 6–7/group). Two hours after serum transfer, mice were aerosol challenged with 18–30 LD50 of Bpm K96243. Survival of mice from PBS, CLH001, and PBK001 groups were observed for 21 days. *p < 0.05, **p < 0. 01, ***p < 0.001, ****p < 0.0001, n.s. = not significant. P values were determined using unpaired t-tests.
