Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2002
Publication Date: 10/10/2002
Citation: Virology. 2002. v. 302. p. 9-20.
Interpretive Summary: The mechanisms mediating protective immunity against Porcine Reproductive and Respiratory Syndrome (PRRS) are not well understood. Knowledge of the protective mechanisms is required for the rational development of improved vaccines for PRRS, the most important infectious disease affecting the U.S. swine industry. The objective of this study was to determine whether or not antibodies to PRRS virus alone were capable of protecting swine. Antibodies from swine immunized against PRRS virus or pseudorabies virus (PRV) were transferred into pregnant sows. The sows were challenged with virulent PRRS virus and the number of pigs born alive counted. Sows that received anti-PRRS virus antibodies were fully protected against abortion while sows that received anti-PRV antibodies had severe abortion, stillbirth and weak pigs. These results indicate that antibodies alone are sufficient to protect pigs against PRRS virus. Further studies to determine which viral proteins elicit protective antibodies are required for rational subunit vaccine design.
Technical Abstract: Immune mechanisms mediating protective immunity against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) are not well understood. The PRRSV-specific humoral immune response has been dismissed as being ineffective and perhaps deleterious for the host. The function of PRRSV-neutralizing antibodies in protective immunity against infection with a highly abortifacient strain of this virus was examined by passive transfer experiments in pregnant swine. The totality of a group of pregnant females (n=6) that received PRRSV-neutralizing immunoglobulin (Ig) were fully protected from reproductive failure as judged by viability of offspring at birth and at weaning (15 days of age). On the other hand, the totality of animals in a matched control group (n=6) receiving anti-Pseudorabies Virus Ig exhibited marked reproductive failure with negligible offspring survival. Besides protecting the pregnant females from clinical reproductive disease, the passive transfer of PRRSV Ig cleared the challenge virus from the dams and prevented its vertical transmission, as evidenced by the complete absence of infectious PRRSV from the tissues of the dams and lack of infection in their offspring. In summary, these results indicate that PRRSV neutralizing Igs constitute a solid correlate of protective immunity against PRRSV and furthermore that these Igs can provide sterilizing immunity in vivo.