Figure 6. Passive immunization using Abs against Dll1 abrogates survival rate, lung pathology, and viral load.

(A) Western blot analysis showed the specificity of polyclonal rabbit anti-Dll1 using OP9 cells transfected with various Notch ligands. (B) The level of Dll1 in lung macrophages (CD11b⁺F4/80⁺) was determined with flow cytometry using an Ab against Dll1 at day7 post infection; PBS treated mice with either control Abs (Orange) or Abs directed against Dll1 (Blue), H1N1-infected mice with either control Abs (Red) or Abs directed against Dll1 (Green). (C) Survival rate of WT mice treated with either control Abs (black) or Abs directed against Dll1 (red) after intranasal injection with PBS only (dotted line) or H1N1 (solid line). **P<0.01 compared with control Ab group. (D) Histological appearance of lungs isolated from WT mice treated with either control Abs or Dll1 Abs at day 2 and 7 after influenza virus infection. H&E staining. Original magnification, ×40; ×200. (E–G) Viral load in WT mice treated with control Abs or anti-Dll1 Abs at 2 and 7 days after infection of influenza virus (1×10⁴ PFU), measured by TCID₅₀ (E) and, M1 (F) and NS (G) H1N1 viral mRNA. Viral mRNAs are expressed as RNA copies normalized to GAPDH expression levels, as determined by real-time PCR. (H) mRNA expression of Hes1 in mice treated with control Abs or anti-Dll1 Abs 2 and 7 days after infection of influenza virus. *P<0.05 compared with control Ab group. Data shown indicate mean ± SEM and are from a representative experiment of 3 independent experiments. Each time point represents 5 mice per group.