Fig. 1.

Serum PDCoV-specific IgG, IgA and VN Ab titers in pigs after two challenges. (a) Serum PDCoV-specific IgG Ab titers in pigs after two challenges. (b) Serum PDCoV-specific IgA Ab titers in pigs after two challenges. (c) Serum VN Ab titers in pigs after two challenges. Blood samples were collected from each pig at 0, 7, 14, 21, 28, and 35 days after the first challenge, and the PDCoV-specific IgG and IgA Ab titers were measured using an indirect ELISA developed in our laboratory. The average OD value in each group (n = 5) was measured, and the standard deviation (SD) was plotted at each point. Significant differences among the five groups at 7-35 dpi are indicated by asterisks (p < 0.05). In VN tests, serum samples were heat-inactivated for 30 min at 56 °C before being serially diluted twofold (50 µL) and mixed with a volume equal to 200 TCID₅₀ of the CH/XJYN03/2016 strain. The samples were examined using an inverted microscope on day 5. The VN Ab titer in each serum sample was measured three times, and the average was calculated. Significant differences are indicated by asterisks (p < 0.05)