Fig. 5.

A diagram illustrates polyPLA. PolyPLA quantifies antibody-antigen binding avidity. Reference polyclonal antiserum (for antigenic analyses) or anti-NP monoclonal antibody (mAb) (for normalization) is biotinylated and then labeled using sodium azide-linked oligonucleotide probes. The labeled polyclonal antiserum or monoclonal antibody is incubated using a reference (virus) or testing antigen and ligated with the two oligonucleotides linked to the antibodies are ligated followed by qPCR, which is used to determine the amplification signals and quantify antibody-antigen binding avidity. The resulting cycle threshold (Ct) values of the polyclonal antisera and antigens are normalized by those by anti-NP monoclonal antibody and antigens and then analyzed for antigenic differences, and the normalization will ensure the equal amount of antigens in antigenic analyses. This figure was adapted from Martin et al. [302]