Figure 4.

Defective induction of IFN-γ production in IRAK-deficient mice. (A) Defective IFN-γ mRNA expression induced by IL-18 in IRAK-deficient Th1 cells. IRAK-deficient [IRAK(−)] and wild-type Th1 cells were stimulated with IL-18 (50 ng/ml), IL-12 (10 ng/ml), or a combination of IL-18 and IL-12 for 2 h. Total RNA was prepared from the cells and IFN-γ expression was determined by Northern blot analysis using ³²P-labeled IFN-γ cDNA probe. The blots were stripped and hybridized to glycerol-3-phosphate dehydrogenase (G3PDH) cDNA for normalization. (B) Reduced induction of IFN-γ production in P. acnes–primed and LPS-challenged IRAK-deficient mice. IRAK-deficient [IRAK(−)] and wild-type mice were intraperitoneally injected with 2 mg of heat-killed P. acnes. Mice were intravenously injected with 1 μg LPS on day 7. Serum samples were collected 6 h after LPS challenge and levels of IFN-γ in sera were determined by ELISA. (C) Total spleen RNA was prepared from P. acnes– and LPS–treated mice. IFN-γ expression was determined by Northern blot hybridization using ³²P-labeled IFN-γ cDNA probe. The blot was stripped and hybridized with IL-18 cDNA probe.