FIG. 2.

CD1d-dependent NKT activation enhances in vitro lethal toxin neutralization. Sera from experiments with results shown in Fig. 1 were used for in vitro neutralization assays as described in Materials and Methods. Briefly, RAW267.4 macrophages were untreated (none) or incubated with toxin alone or toxin mixed with sera from naïve and immunized mice before assessing viability. Each data point represents the percent cell viability conferred by serum from individual mice. All samples were analyzed in duplicate. Asterisks indicate statistically significant differences between PA-immunized versus PA plus α-GC-immunized groups. (a) Effect of serum dilution on resistance to the toxin. (b) Effect of increasing toxin concentration on neutralization.