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 leads to increased infection and exacerbation of disease severity in CHIKV-infected adult mice. To further establish and evaluate the contribution of antibody-mediated enhancement in CHIKV infection, in vivo infections were performed in two different and well-characterized CHIKV mouse models that mimic disease in humans [40] [41] [42] . Using the joint footpad model 41-48 , 3 weeks old wild-type (WT) C57BL/6 mice were inoculated with 10 6 plaque forming unit (PFU) of CHIKV in Figure 1 . Enhancement of CHIKV infection in purified primary human cells. Primary human (a,c) monocytes and (b,d) B cells (2 × 10 6 cells per infection) were infected with CHIKV (moi 10) in the presence (enhanced) or absence (non-enhanced) of diluted CHIKV-specific patient plasma containing total IgG at a concentration of 3.6 ± 2.9 μg/ml. (a,b) Detection of CHIKV antigen and (c,d) viral RNA load were determined at 0 and 6 hpi. Level of CHIKV antigen detected is expressed as fold enhancement relative to the non-enhanced infection controls. Data shown are mean ± SD from 3 independent experiments by parametric unpaired t test (**P = 0.0015 for 0 hpi monocytes; *P = 0.0458 for 0 hpi B cells and **P = 0.0053 for 6 hpi B cells). Expression of FcγRs in (e) monocytes and (f) B cells. Primary human (g) monocytes and (h) B cells (2 × 10 6 cells per infection) were treated with 10 μg of FcγRs blocking agent prior to CHIKV infection (moi 10) under enhancing conditions (as above). Percentage of infection is expressed as level of CHIKV antigen detected relative to the non-treated infection controls at 0 hpi. Data are presented as mean ± SD from 4 independent experiments by Mann-Whitney U test (*P = 0.0286 for monocytes and *P = 0.0143 for B cells). the right footpad, followed by intra-peritoneal administration of diluted CHIKV-specific mice sera containing total IgG at a concentration of ~2 μg/ml. Disease progression was monitored daily for viremia and degree of joint inflammation at the footpad. Mice infected under enhancing conditions had significantly higher viral RNA load . CHIKV (moi 10) was used to infect (b) non-FcγR-expressing, (c) FcγRI-expressing, (d) FcγRII-expressing and (e) FcγRIII-expressing ST486 cell lines (2 × 10 6 cells per infection) in the presence (enhanced) or absence (non-enhanced) of diluted patient plasma containing total IgG at a concentration of 3.6 ± 2.9 μg/ml (n = 9). Level of CHIKV antigen was determined at 0 and 6 hpi. Level of CHIKV antigen detected is expressed as fold enhancement relative to the non-enhanced infection controls. Data are presented as mean ± SD by Mann-Whitney U test (***P < 0.0001 for level of CHIKV infection observed at both 0 and 6 hpi in FcγRI and FcγRII expressing cells). during the acute phase of the disease (Fig. 5a ) and endured a more pronounced inflammation at the infected joint footpad (Fig. 5b) . Tissue immune-phenotyping (Fig. S4 ) further revealed higher levels of infiltration of neutrophils and possibly CD4+ T cells into the joint footpad at 6 days post-infection (dpi) during enhanced CHIKV infection (Fig. 5c ). Moreover, a much lower number of CD4+ T cells and monocytes were present in the popliteal lymph node (pLN) draining the right footpad (Fig. 5d) , indicating the possible egress of these cells from the pLN into the circulation or infected tissues during enhanced infection. Gene expression studies also revealed higher levels of IFNγ as well as IL-10 in the inflamed footpad during