Cross-neutralizing activities. Neutralization of PERV with sera specific for p15E, gp70 and p27Gag of KoRV and PERV. The Y-axis indicates the percentage of reduction of integration of viral DNA into cellular DNA (infection) in the presence of immune sera. Sera were used at dilutions of 1:10 to 1:320 and integration was measured by real time PCR. The dashed line indicates 50% neutralization.