2.4 Antibody titer detection

M2e- and PCV2-specific antibodies in sera were determined by indirect ELISA using 1 μg/mL of synthesized M2e peptides (Fig. 1c) as coating antigens. Twofold serially diluted immune serum samples were added into the ELISA plates, followed by HRP-conjugated goat anti-mouse IgG. TMB was used as substrate to develop the color reaction. The highest dilution which showing over twofold OD450 readout than that of the control sample as the antibody endpoint titer. For the detection of PCV2-specific antibodies, commercial PCV2 antibody test kit (BioChek, Reeuwijk, Holland) was utilized. The ELISA plates were coated with purified and inactivated PCV2. Immunoperoxidase monolayer assay (IPMA) was used to evaluate the PCV2-specific neutralizing antibodies in sera, according to the previous method (Ding, Jin, Chen, et al., 2019).