BPV1 VLP (a) or BPV2 VLP (b) were analyzed under non-denaturing (native) conditions using antisera raised to BPV1-L1 and BPV2-L1 VLPs, and mAb directed to conformational BPV1 epitopes. VLPs were incubated with 10-fold serial dilutions (10−2 to 10−5) of antibodies. Data are expressed as mean OD±SD of triplicate wells. Neutralization capacity of antibodies at final dilution of 1:100 was determined by C127 focus-forming neutralization assays using BPV1 (a) or BPV2 (b) native virions. +, Neutralizing, −, non-neutralizing; n.d., not determined.