Reactivity of six PCV2 isolates with mAb 8E4 by the IPMA, serum neutralization assay and capture ELISA. (a) IPMA reactivity of PK-15 cells inoculated with PCV2a/LG (1 and 2), PCV2a/CL (3 and 4), PCV2a/JF2 (5 and 6), PCV2b/YJ (7 and 8), PCV2b/SH (9 and 10) and PCV2b/JF (11 and 12), against PCV2-positive serum and mAb 8E4. Odd numbers represent PCV2-positive serum, whereas even numbers show mAb 8E4. (b) The neutralizing activity of mAb 8E4 was expressed as the percentage reduction in the number of infected cells in comparison with negative control. A mean neutralizing activity of > 50% was considered to represent neutralization. Error bars represent the standard deviations. (c) For the capture ELISA, cultures of six PCV2 isolates, recPCV1/G and PK-15 cells were tested with HRP-conjugated 8E4. P/N > 2.1 was regarded as a positive result. Error bars represent the standard deviations.