Fig. 4.

Specific humoral immune responses detected in infected ferrets. Serum from ferrets surviving an initial infection with rHB29 (A), rHB29NSsP₁₀₂A (B), or rHB2912aaNSs (C) were analyzed at 0 (gray), 8 (red), 14 (blue) and 58 (green) days p.i. Positive ferret serum (black) was added as a control for comparison. Humoral immune responses were analyzed using a nucleocapsid protein (N)-based ELISA. Optical density (OD) was measured with a spectrometer (iMark Microplate Reader; Bio-Rad) at 450 nm. The cutoff value was set at an OD value of 0.5 and is indicated as a dashed line in A–C. Serum neutralization assays with rHB29 (D), CB8/2016 (E), and CB1/2014 (F) virus strains were analyzed by FRNT₅₀ at 0, 8, 14, and 58 d p.i. The asterisks indicate significance compared to the respective serially diluted day 0 p.i. sample (A–C) or to the rHB29-immunized serum test (D–F), assessed by one-way ANOVA with Dunnett multiple comparison test. *P < 0.05, **P < 0.01, or *** < 0.0001 (A–C); *P = 0.0165 and **P < 0.0001 (D); *P = 0.0061, **P < 0.0001, (E); and *P = 0.0328, **P < 0.0001, and ***P = 0.0001 (F).