FIG. 1.

S. pneumoniae induces production of less TNF, IFN-γ, and IL-12 from PBMC than other Streptococcus viridans group bacteria. PBMC (2 × 10⁶ cells/ml) from three blood donors were stimulated with eight Streptococcus strains, including S. pneumoniae A17, using concentrations of 3 × 10⁷ and 3 × 10⁶ bacteria/ml. Cytokine production was measured using the supernatant after 24 h (TNF, IL-12, IL-6, IL-8, IL-10) or 5 days (IFN-γ). The bars and error bars indicate the median cytokine concentrations produced and interquartile ranges. The concentrations of cytokines produced in response to S. pneumoniae compared to the concentrations produced in response to other streptococcal strains were analyzed using the Mann-Whitney test. *, P < 0.05; **, P < 0.01.