(a-c) Analysis on day 2 after infection with PR8 virus of wild-type mice (WT) or Ripk2−/− mice injected intraperitoneally with control rabbit serum and Ripk2−/− mice injected intraperitoneally with anti-IL-18 neutralizing antiserum (αIL-18Ab) 3 h before infection, for IL-18, IFN-γ and CCL2 amounts in whole lung homogenates (a; t.p., total protein), and for neutrophil numbers by immunohistochemistry (b) and by flow cytometry (c). Original magnification, ×20. 