Fig. 3. Alternatively activated macrophages are more readily infected with A/WSN/33 than classically activated macrophages. BMDMs derived from (a–e) 129Sv/Ev and (f–j) IFN-γ R^{− / −} mice were cultured in medium containing M-CSF alone (a, f) or treated with IFN-γ (b, g) or IL-4 (c, h) for 16 h and infected with 10 p.f.u. A/WSN/33 per cell followed by staining with antiserum to virus antigens. The percentage of cells positive for antigen was quantified at 6 (d, i) and 48 h (e, j) *P < 0.05; ***P < 0.001.