Antibody responses play a crucial role in defense against many viral diseases, and knowledge of critical functions can be used to monitor and predict vaccine efficacy. We have identified the features of key antibodies produced in response to PRRSV, and have defined the genetic elements that can give rise to anti-PRRSV antibodies. This information can, and will be, used to identify antibodies originating in pigs responding to a PRRSV infection and characterize the neutralizing activity. This knowledge will help to focus vaccine strategies and provide therapeutic reagents to reduce disease severity.