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).