Fig. 3.

Neutralising antibodies elicited by the different mouse immunisation protocols. Virus neutralisation assays were performed on Vero cells after each immunisation. Plaque reduction was quantified as compared to the control, in which the viral inoculum was incubated with the preimmune serum, and expressed as percentages of inhibition of infectivity. (A) Except for Group 2 (G2), all of the groups of mice raised neutralising antibodies against IHD-J, and inhibition of infectivity generally increased after the second immunisation. (B) Sera from mice 1, 4, 7 and 8 of Group 5 showed significantly higher inhibition of infectivity, although not all of these mice were protected. Conversely, mouse 5 of Group 5 was protected in the absence of significant levels of neutralising antibodies. Statistical significances using the Student t-test are shown: (^**) p < 0.01; (^***) p < 0.001.