Induction of auto-anti-idiotypic antibodies specific for antibodies to matrix and envelope glycoprotein from pigs experimentally infected with porcine reproductive and respiratory syndrome virus.

Auto-anti-idiotypic antibodies (Aab-2s) specific for antibodies against envelope glycoprotein GP5 were previously identified in 10 of 12 pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). In this study, we report in addition the induction of Aab-2s specific for antibodies against matrix (M) and envelope glycoprotein GP5 antigens in 38 of 47 pigs experimentally infected with PRRSV. Two sets of Aab-2s were induced in the sera, one at 21 days post-infection (DPI) and peaked on 35 DPI and another at 49 DPI and peaked on 77 DPI. The Aab-2s induced at an early stage were from non-virus carrier pigs as defined when they were euthanized on and after 77 DPI. In contrast, the Aab-2s induced at a later stage were from virus carrier pigs. These Aab-2s possessed the characteristics of internal image Ab-2s and recognized shared idiotypes on swine and murine antibodies to the GP5 and M antigens of PRRSV. This study further demonstrates that, during the antibody responses to PRRSV infection, Aab-2s specific for both anti-M and anti-GP5 antibodies were induced. More importantly, the early and late Aab-2s possessed different idiotype-binding specificities. By detecting and characterizing these Aab-2s, it may be possible to identify whether pigs infected with PRRSV will clear the virus or become virus carriers.