Multiplexed Fc array assays reveal the influence of TLR3 on the Th1-biased humoral response induced in mice following live-attenuated RVFV vaccination

Rift Valley fever virus (RVFV) can cause severe disease in humans and livestock. Several vaccine candidates are immunogenic and protective in pre-clinical animal models. Reported measurements of humoral immunity following vaccination typically assess antigen-specific activity, such as virus binding or neutralization, but do not consider the role of the Fc region. To address this knowledge gap, multiplexed Fc array assays were developed to characterize the Fc profile of antigen-specific antibodies following RVFV vaccination. The RVFV nucleocapsid protein (N) and glycoproteins (Gn/Gc) were conjugated to magnetic microspheres, and monoclonal antibodies were used to optimize assay conditions. Sera from vaccinated mice were incubated with the conjugated microspheres to capture antigen-specific antibodies, and then various detection reagents were used to measure the isotype of the antibodies and their ability to bind Fc receptors (FcRs) or complement (C1q). Two studies involving mice vaccinated with live-attenuated RVFV ΔNSsΔNSm or ΔNSs were used to demonstrate the utility of these assays. In WT C57BL/6 mice, both ΔNSsΔNSm and ΔNSs induced a high magnitude of IgG2c antibodies, indicative of a Th1-biased response; these antibodies also bound the four murine FcRs and C1q. However, following ΔNSs infection of a panel of innate immune knockout (KO) mice, several strains of KO mice, especially TLR3 KO, exhibited a reduced magnitude of IgG2c antibodies, demonstrating the impact of innate immunity on the Th1-biased response. Overall, the multiplexed Fc array assays performed as expected and can be applied to other RVFV vaccine platforms in the future to help inform rational vaccine design. IMPORTANCE: There are currently no approved vaccines to prevent RVFV infection in humans. While some vaccine candidates exist, such as the live-attenuated ΔNSsΔNSm vaccine, most immunogenicity studies do not consider the contribution of the Fc region to antibody quality. In this study, multiplexed Fc array assays were developed to assess the Fc profile of antigen-specific antibodies following RVFV vaccination. These assays proved to be useful in identifying a Th1-biased response induced by RVFV ΔNSsΔNSm and ΔNSs and in identifying the contribution of innate immunity to this response. These assays can be applied to other RVFV vaccine platforms, such as mRNA and protein vaccines, to fully characterize the quality of an antibody response following vaccination.