PBMC were co-incuabated for 24 hours with iRBC (n=29), LPS (n=8), BCG (n=8), IL-12 + IL-18 (n=21) or IFN-α + IL-18 (n=17). **A:** The proportion of CD56^{bright} NK cells (grey circles) or CD56^{dim} NK cells (black circles) which stain positively for intra-cellular IFN-γ. Paired T test comparing CD56^{bright} to CD56^{dim} NK cells: iRBC, t=3.7, df=35, p=0.0007; LPS, t=3.8, df=15, p=0.0016; BCG, t=3.7, df=15, p=0.0022; IL-12 + IL-18, t=7.0, df=20, p<0.0001; IFN-α + IL-18, t=2.5, df=15, p=0.0229. **B:** The mean fluorescence intensity of staining for IFN-γ in CD56^{bright} and CD56^{dim} NK cells. Paired T test comparing CD56^{bright} to CD56^{dim} NK cells: iRBC, t=3.6, df=20, p=0.0020; LPS, t=4.4, df=15, p=0.0005; BCG, t=3.5, df=15, p=0.0030; IL-12 + IL-18, t=7.0, df=29, p<0.0001; IFN-α + IL-18, t=2.8, df=17, p=0.0123. **C:** The proportion of peripheral blood IFN-γ^{+} NK cells which are either CD56^{bright} or CD56^{dim}. Paired T test comparing CD56^{bright} to CD56^{dim} NK cells: iRBC, t=11.5, df=28, p<0.0001; LPS, t=5.0, df=15, p=0.0002; BCG, t=8.0, df=15, p<0.0001; IL-12 + IL-18, t=9.7, df=20, p<0.0001; IFN-α + IL-18, t=35.4, df=14, p<0.0001. Results of paired t tests are indicated as follows: *, *p*< 0.05; **, *p* < 0.01; ***, *p* < 0.001.

iRBC, *Plasmodium falciparum*-infected red blood cells, LPS, *Salmonella typhimurium* lipopolysaccharide; BCG, *Mycobacterium bovis* Bacillus Calmette-Guérin.

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