FIG 6.

Applications of the VLP system with incorporated mutations. (A) Endpoint titration of sera from VLP-immunized animals. ELISA plates were coated with WT-VLP, and one representative serum sample from each VLP-immunized mouse was used to calculate the endpoint titer. (B) Neutralization of VLP binding to cells. Labeled VLPs were incubated with the indicated dilutions of sera prior to binding with Vero cells. VLP binding to cells after preincubation was analyzed by flow cytometry and quantified. Student’s t test was used for statistical analysis. Error bars represent SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001. (C) Live virus neutralization using sera from VLP-immunized animals. Virus was incubated with heat-inactivated sera from VLP-immunized animals prior to attachment to Vero cells. The serum dilution which resulted in a 50% reduction of plaque numbers compared to preincubation with serum from PBS-immunized animals was plotted. Each point represents a different mouse serum. (D) Binding affinity of VLPs with recombinant ACE-2 was calculated using microscale thermophoresis.