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.

Antibody-mediated enhancement of CHIKV infection in mouse macrophages. Before studying the impact of CHIKV antibody-mediated enhancement in mice, in vitro CHIKV infections were first performed in the RAW264.7 mouse macrophage cell line. RAW264.7 cells have been used in several studies to investigate the effects of antibody-mediated enhancement of infection in RRV 31,32 , a closely related alphavirus. RAW264.7 cells have high levels of FcγRII/III (Fig. 3d) . As a result, an increased in CHIKV infection was observed at 6 hpi in the presence of sub-neutralizing levels of CHIKV-specific mouse sera containing ~2 μg/ml of total IgG antibodies ( Table 1) (Fig. 3e) . The increased in CHIKV infection was further complemented with higher viral RNA load (Fig. 3f) . Given that enhanced CHIKV infection in RAW264.7 cells led to both increased levels of CHIKV antigen detected and viral RNA load, the consequences of this enhancement was further studied via gene expression analyses on the Type-I Interferon (IFN) and pro-inflammatory pathways (Fig. 4a) . Expectedly, high levels of several pro-inflammatory and anti-viral genes such as IL-6, iNOS, IFNα, IFNβ, IRF3, IRF9, Viperin and ISG15 were detected starting at 6 hpi when CHIKV infection was enhanced (Fig. 4b) .