Antibody-mediated enhancement aggravates chikungunya virus infection and disease severity

Lum, Fok-Moon; Couderc, Thérèse; Chia, Bing-Shao; Ong, Ruo-Yan; Her, Zhisheng; Chow, Angela; Leo, Yee-Sin; Kam, Yiu-Wing; Rénia, Laurent; Lecuit, Marc; Ng, Lisa F. P.

to CHIKV infection under enhancing conditions as described above. Immediately after the virus overlay was removed, cells were washed and harvested for downstream procedures as mentioned above. For FcγRII blocking, mouse anti-human CD32 antibodies (Stemcell) were used instead. Results are expressed as % infectivity relative to non-treated-enhanced infections. Reduction in infectivity was calculated according to the equation: % infectivity = 100 × Level of CHIKV antigen detected from treated-enhanced infection group / Level of CHIKV antigen detected from non-treated-enhanced infection group). Viral RNA load assay. Viral RNA was extracted using QIAamp Viral RNA Mini Kit (QIAGEN), following manufacturer's instructions. Viral RNA load was subsequently measured using real time quantitative reverse transcription PCR (qRT-PCR) utilizing QuantiTect ® Probe RT-PCR kit (QIAGEN) modified from a previously described method to detect negative-strand nsP1 RNA 70,71 . Flow cytometry. Fixed cells were permeabilized with FACS permeabilizing solution 2 (BD Biosciences).