Analysis by HI assay of the reactivity of sera obtained from pigs at different ages against PToV-HE52.7 and PToV-HE52.11. Extracts from BSC40 cells infected (MOI 5) for 24 h with rVV-HE52.7 (panels A, C and E) or rVV-HE52.11 (panels B, D and F) and treated with DFP were diluted to contain 4 HAU in 25 μL PBS and incubated (1 h at 37 °C) with two-fold serial dilutions of pig sera prior to adding the mouse RBC. Serum samples were obtained from animals belonging to three litters (litter A, panels A and B; litter B, panels C and D; litter C; panels E and F) at different ages (1, 3, 7, 11 and 15 weeks) and from their sow (one-week post-farrowing). (G) Percentage of HI positive animals against PToV-HE52.7 (blacK bars) and PToV-HE52.11 (grey bars) over the period studied. (H) Comparative analysis of HI titers of each serum sample against PToV-HE52.7 and PToV-HE52.11 proteins. The results shown in the graphs are representative of two independent experiments.