FIG 2.

Immunization with HMPV VLPs induces F-specific antibodies. (A) Schematic showing the immunization protocol. B6 mice (five per group) were immunized two times, 14 days apart, by i.p. injection with VLPs containing either HMPV M (M-VLP) or M plus F (F-VLP) protein. VLPs were administered alone, with TMG adjuvant, or with αGC adjuvant. Negative-control mice were injected with purified supernatant from untreated 293-F cells (mock VLPs). Positive-control mice were infected i.n. with HMPV on day 0. Blood was collected at the time points indicated and at euthanasia to determine the production of F-specific and neutralizing antibodies. (B to J) HMPV F-specific antibody levels in serum samples were measured by ELISA. Preimmune serum was collected on day 0. Postinfection and postimmunization serum samples were collected 5 days after an HMPV challenge. The absorbance resulting from serum antibody binding to plates coated with recombinant F protein is shown for each vaccination group as follows: panel B, mock VLPs; panel C, HMPV; panel D, M-VLP; panel E, M-VLP plus TMG; panel F, M-VLP plus αGC; panel G, F-VLP; panel H, F-VLP plus TMG; panel I, F-VLP plus αGC. Absorbance data are shown as the mean ± the SEM for five mice from three independent ELISAs. Nonlinear regression analyses were performed for groups with F-specific antibodies and used to calculate reciprocal serum titers at half-maximal absorbance (IC₅₀), shown in panel J. Data points represent individual mice, and the bar depicts the mean IC₅₀ titer of each immunization group. Comparisons of multiple groups were made by one-way ANOVA for the P values shown in panel J.