FIG. 3.
Replication of H7 wt challenge viruses in the respiratory tract of mice immunized with the H7N7 NL/03 ca virus. Groups of four mice were immunized with 1 dose (upper panel) or 2 doses (lower panel) of 106 TCID50/mouse of the H7N7 NL/03 ca virus (○ and □) or were mock immunized (L-15) (• and ▪) and were challenged with 105 TCID50/mouse of each indicated virus. The H7N7 NL/03 wt virus is the homologous HPAI virus, and the H7N3 ck/BC/04 wt and tk/EG/63 wt viruses are heterologous HPAI viruses from North American and Eurasian lineages. The H7N1 tk/Italy/99 wt virus is a heterologous LPAI virus from the Eurasian lineage. Nasal turbinates (A) and lungs (B) were harvested 2 days (○ and •) and 4 days (□ and ▪) following challenge. Virus titers are expressed as log10 TCID50/g of tissue. The lower limit of detection is indicated by the dashed horizontal line. An asterisk indicates a statistically significant (P < 0.05) reduction in virus titers compared to the titers in the mock-immunized group.