Figure 2. FI-RSV immunization of RSV-primed mothers and its effect on RSV infection of pups.
(A) Diagram of the experiment. Female CR were primed by infection with RSV A/Long (105 PFU i.n.). Eight weeks later primed females were divided into two groups and immunized with FI-RSV Lot 100 (100 µl i.m. of a 1:125 dilution of the original Lot 100 vaccine) or left unvaccinated (−). All females were set in breeding pairs at 10 weeks after RSV-priming, females previously vaccinated with FI-RSV were boosted during pregnancy (12 weeks after RSV priming), and began delivering pups after week 14. Two sex-balanced groups were formed from the pups: pups challenged with RSV at 1 week of age and pups challenged with RSV at 4 weeks of age (both groups were sacrificed 4 days p.i.). Mothers remaining on the experiment were bled at week 22 and challenged with RSV A/Long (105 PFU i.n.) for sacrifice 4 days later. (B) Pups delivered by RSV-primed mothers vaccinated with FI-RSV or unvaccinated (−) were bled at 1 or 4 weeks of age and serum NA titers were determined. Bars represent mean ± SEM. (C) Lung and nose mean viral titers ± SEM in pups (1-week old) born to RSV-primed mothers that were vaccinated with FI-RSV or unvaccinated (−). A slight but significant increase in protection of the lung and the nose was detected in animals born to mothers vaccinated with FI-RSV (* p<0.01 by Student t Test) in 1-week old pups. Neither lung nor nose of animals challenged at 4-weeks of age showed protection in the group born to FI-RSV-vaccinated mothers. (D) Lung pathology scored in animals (1- and 4-weeks old) born to RSV primed-mothers vaccinated with FI-RSV or unvaccinated. Numbers in parentheses above each bar represent the number of animals used for analysis. (E-F) Expression of mRNA for IFN-γ and IL-4 in RSV-infected (+) or uninfected (−) animals born to RSV-primed mothers that were vaccinated with FI-RSV or unvaccinated (−) during pregnancy. Unchallenged pups from naïve mothers were used as control for base-level gene expression (c). Bars represent mean ± SEM. (G) NA titers of RSV-primed mothers that were vaccinated with FI-RSV- or unvaccinated (−) before challenge on week 20 post-priming (left panel) and lung histopathology scores in the same animals determined at day 6 post-challenge (right panel). Transversal lines represent mean values in each group.