Fig. 6.

Effect of replication and route of immunization on the immunogenicity of HPIV3/EboGP. A. Effect of replication. Guinea pigs (four animals per group) were infected IN with HPIV3/EboGP at a dose of 4×10⁶ TCID₅₀ or with an equivalent amount of UV-inactivated virus. Sera were collected 29 days post-infection and the titers of HPIV3- and EBOV-specific serum antibodies were determined by HAI and ELISA respectively. Serum antibody titers are expressed as reciprocal log₂ of endpoint dilutions and shown as mean titers ± SE with the P values indicated at the top. In sera of mock-infected animals (representing 5 animals from a separate experiment), the level of HPIV3-specific antibodies was below the detection level (2 log₂), and is indicated with an asterisk. In the HPIV3/EboGP-UV group, the level of HPIV3-specific antibodies in three out of four animals was below the detection level, and the value of 2 log₂ was assigned for calculation purposes. The detection limit of the HAI assay is 2.0 log₂. B. Effect of the IN versus IM route of immunization. Guinea pigs were immunized with 4×10⁶ TCID₅₀ of HPIV3/EboGP by the IN or IM route (six animals per group), or 4×10⁶ TCID₅₀ of HPIV3 by the IM route (three animals). Sera were collected on day 30 after immunization and the titers of HPIV3- and EBOV-specific serum antibodies were determined as above. In addition, sera from nine animals collected on day 28 after IN infection with 4×10⁶ TCID₅₀ of HPIV3 from a previous experiment (Fig. 5) were analyzed in parallel for comparison. In an uninfected group (which consisted of two animals from a separate experiment), the level of HPIV3-specific antibodies was below the detection level, and is shown with an asterisk. In the HPIV3-immunized group, the level of EBOV-specific antibodies was below the detection level and is shown with a plus. The detection limit of the HAI assay was 5.32 log₂.