FIG. 3.
Humoral immune responses (A) and LRT- (B) and URT- (C) protective efficacies in mice following immunization with carrier-protein-coupled synthetic peptides. Groups of 7 to 12 mice were immunized i.p. at 2-week intervals two or three times with peptide coupled to P40 carrier protein in 200-μl volumes containing 20% (vol/vol) Alhydrogel. Mice immunized with P40-G174–187ΔC, P40-G172–187, or P40-G164–176 were primed with 20 μg of protein followed by two boosters of 100 μg each. Those immunized with P40-CysG190–204 received three doses of 20 μg of protein. Finally, mice immunized with P40-CysG144–159 or P40-G144–159Cys were immunized twice with 20 μg of protein. Controls included animals immunized with PBS. All mice were bled 2 weeks after the last immunization, challenged 1 week later with 105 TCID50 of RSV-A, and sacrificed 5 days postchallenge. Sera were tested in ELISAs against RSV-A. Ten percent lung homogenates were prepared. Nasal tracts were rinsed by forcibly injecting 1.5 ml of virus transport medium through the nasopharyngeal cavity and recovering exudate from the nares. LRT and URT virus titers were determined as described in Materials and Methods.