Fig. 4.

Determination of recall nAb response in immunised mice using the ZIKV luciferase reporter assay. (a) Determination of ZIKV nAb titre in the same pooled immune serum as in Fig. 3d, but determined using ZIKV RVPs. The data are represented as percent infection (in terms of Renilla luciferase activity of ZIKV RVPs) as a function of immune serum dilution, with luciferase activity of ZIKV RVP in absence of immune serum taken to represent 100% infection. Virus neutralisation curves obtained using pooled sera from mock-immunised and ZIKV-80E NP-immunised mice are shown using solid grey and solid purple curves, respectively. (b) A subset (n = 5) of mice was bled ∼4 months after the 3rd immunisation dose (on day 159) and given a booster dose of alum-formulated ZIKV-80E NPs (4th dose) the next day to assess recall response. Ten days later (day 170) the mice were bled again. Sera pools corresponding to day 159 (dashed purple curve) and 170 (solid purple curve) were assayed for nAb titres as described in panel ‘a’. Mock-immune serum analysed in parallel is shown by the solid grey curve. The dashed horizontal line in both panels denotes 50% infection based on ZIKV RVP luciferase activity.