AG129 or congenic WT mice were primed with al-UV-DENV2 on days −14 and −5. On day 0, serum was collected and 200 μl of serum from AG129 mice (A) or WT mice (B) were transferred i.v. into naïve AG129 recipient mice one day prior to challenge with DENV2. Viral RNA levels were measured in the liver on day 3 after infection. The isotype and ADE control groups (described in fig. 1) received no serum and were challenged on day 0. In C, serum from al-UV-DENV2-primed WT mice was left untreated (untr.) or heat-inactivated (inact.) before transfer into naïve AG129 mice one day prior to challenge. In one group of recipients, IgG purified from al-UV-DENV2-primed WT serum were transferred prior to challenge. Viral RNA titers were measured by qRT-PCR in the liver on day 3 post-infection.
Each symbol represents one mouse, the experiment in A was repeated twice with similar results; see also supplementary figure S1 and S2.