FIG 1.

Type I IFN signaling is required for IL-18 production in response to S. pneumoniae. (A to F) Adherent PECs from C57BL/6 (WT) and IFNAR1^−/− mice were left uninfected or infected with S. pneumoniae D39 at an MOI of 10. Gentamicin (final concentration of 100 μg/ml) was added to the cultures 8 h after infection, and culture supernatants were collected after an additional 16 h of incubation (24 h after infection). Levels of IL-18 (A), IL-1β (B), IL-1α (C), TNF-α (D), IL-6 (E), and IL-12p40 (F) in the culture supernatants were determined by ELISA. (G to I) Anti-IFNAR1 blocking MAb (10 μg/well) or isotype control Ab (10 μg/well) was added to the cultures at the same time as S. pneumoniae. Levels of IL-18 (G), IL-1β (H), and IL-6 (I) were determined by ELISA. (J and K) Adherent PECs were stimulated with LPS (10 ng/ml) for 3 h and sequentially with nigericin (5 μM). After 21 h, culture supernatants were collected to assess the levels of IL-18 (J) and IL-1β (K) by ELISA. All of the experiments were repeated at least two times, with similar results. Data are presented as the means and standard deviations of triplicate assays. Statistical significance was determined by one-way ANOVA followed by Bonferroni's test. *, P < 0.05; n.s., not significant.