Figure 3.

Analysis of the immunogenicity and efficacy upon lethal RVFV challenge of 40F-p8 virus. Eleven month-old wild type 129Sv/Ev mice (n = 9) were inoculated IP with 10⁴ pfu of 40F-p8. A group of control mice was mock-inoculated (n = 4). (A) Microneutralization assay. Serum samples were taken at day 24 (pre-challenge samples) and titrated for neutralizing antibodies. Sera were assayed in two-fold dilutions ranging from 1/10 to 1/1280. Titer was expressed as log₁₀ of the highest serum dilution causing a CPE reduction of 50%. Assay cut-off was set to 1.0 (dotted line). Negative samples (rendering CPE in all wells at the first dilution assayed) were given an arbitrary value of 0.2. (B) Survival of 129 mice upon RVFV challenge. Differences in survival assessed with the Log-Rank (Mantel–Cox) test. (C) Morbidity upon challenge in vaccinated mice. The graph represents the clinical status of each mouse: D (dead): black bars; S (sick), hatched bars; H (healthy), gray bars. (D) Detection of anti-nucleoprotein antibodies by ELISA. Each symbol corresponds to an individual animal, except for “preimm” samples, corresponding to pools of pre-immune sera. Black/blue symbols: pre-challenge samples. Red symbols: post-challenge samples (14 dpi). Sera were assayed in three-fold dilutions ranging from 1/50-1/109350. Titers are expressed as the last dilution of sera (log₁₀) giving an OD₄₅₀ reading over 1.0. Assay cut-off threshold was set to 1.7 (dotted line, 1/50 serum dilution). For representation, negative samples were given an arbitrary value of 1.4.