Fig. 7.

The capacity of α-DSV4, α-Dengvaxia and α-TV immune sera to cause ADE of ZIKV infection in C57BL/6 Stat2^−/− mice. (a) Groups (n=6-8) of C57BL/6 Stat2^−/− mice were administered mock- (grey), α-DSV4- (orange), α-Dengvaxia- (blue), α-TV DENV- (purple) immune sera or dengue patient plasma (‘Hu-α-DENV’, brown), by passive transfer (20 µl/mouse), two hours before infection with ZIKV strain PRVABC59. A subset (n=3) of challenged mice were bled on day 4 (see panel ‘b’) and euthanised on day 6 post ZIKV challenge (see Fig. 8). The rest of the challenged mice were monitored for up to 15 days (see panels ‘c-e’). (b) Day 4 post infection ZIKV viral RNA in serum, isolated from a subset (n=3) of mice of each of the experimental groups shown in panel ‘a’, was quantified by RT-qPCR as described in methods. ZIKV RNA levels were determined with reference to an in vitro-transcribed RNA standard. Each data point denotes viremia level in a single mouse. The horizontal lines represent the mean viremia levels. ‘ns’ (not significant) and the twin asterisk symbol (very significant), denote statistical significance between the groups indicated, determined by two-way ANOVA with Bonferroni's correction. The rest of the infected mice were monitored for survival (panel ‘c’, ‘ns’ and the single asterisk denote ‘not significant’ and ‘significant’ survival differences for each of the groups with reference to survival of ‘Uninfected’ mice which was 100%), clinical signs (panel ‘d’) and body weight change (panel ‘e’), over the next 15 days. A group of mice which received no treatment (Uninfected, black curves) was monitored in parallel for comparison. In panel ‘d’, clinical scores were based on a 4-point system to grade signs of illness: 0, no symptom; 0.5, mild ruffling of fur; 1.0, ruffled fur; 1.5, compromised eyes; 2.0, hunched back position; 2.5, very limited movement/one leg paralysis; 3.0, no movement and paralysis of both hind legs; 4.0, dead or euthanised. In panel ‘e’, body weight was monitored daily at the same time and expressed as a percent of initial body weight (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).