IKKβ inhibits M1 macrophage activation during infection. (A) IKKβ^ΔMye and IKKβ^f/f control mice were infected by intraperitoneal injection of 5 × 10⁷ CFUs GBS in PBS, and survival was monitored (n = 16–17). (B) Blood was collected at 4 h by retroorbital bleed. Serial dilutions of blood samples were plated in triplicate on Todd-Hewitt agar plates, and CFUs were counted (n = 9–10; **, P = 0.0057). (C) Serum levels of IL-12p70, IL-1β, and spleen IFN-γ were measured by ELISA (n = 7–8; IL-12p70: **, P = 0.0023; IFN-γ: *, P = 0.0148). (D) Total RNA was isolated from the spleens of GBS-infected mice for real-time PCR analysis of IL-12p40 and arginase-1 expression. Data are represented as fold induction of mRNA expression compared with uninfected mice (n = 7–8). (E) MHC class II expression on peritoneal macrophages measured by FACS (percentage of positive cells indicated). (F) Immunohistochemical analysis of NOS2 expression in GBS-infected lungs shows increased expression of NOS2 in alveolar macrophages of IKKβ^ΔMye mice (arrows), whereas expression in bronchial epithelial cells remains unchanged (asterisks). Representative panels are shown from n = 8. Bar, 200 μm.