ARS | Publication request: Antibody repertoire development in fetal and neonatal piglets. XV. Porcine circovirus type 2 infection differentially affects serum IgG levels and antibodies to ORF2 in piglets free from other environmental factors

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 25, 2012
Publication Date: December 17, 2012
Citation: Sun, X., Wertz, N., Lager, K.M., Butler, J.E. 2012. Antibody repertoire development in fetal and neonatal piglets. XV. Porcine circovirus type 2 infection differentially affects serum IgG levels and antibodies to ORF2 in piglets free from other environmental factors. Vaccine. 31(1):141-148.

Interpretive Summary: Infectious diseases cause significant losses for swine producers. Fighting disease involves multiple strategies that includes basic research into how the pig's immune system responds to certain infectious agents like viruses. The goals of such studies are to better understand how the agent might cause disease, how the pig defends itself, and to apply this knowledge towards improving vaccines. Porcine circovirus is believed to negatively affect the pig's immune system which can enhance the disease caused by other bacteria and viruses resulting in a syndrome called porcine circovirus associated diseases or PCVAD. There are two main components to the immune system; one of which produces antibodies against infectious agents. This paper describes a study investigating how porcine circovirus interacts with the antibody producing part of the pig's immune system using germ-free pigs housed in sterile isolators to eliminate environmental influences on the immune response. Based on this initial experiment, the antibody response against porcine circovirus appears to be abnormal suggesting the virus is affecting the immune response. The magnitude of this effect may be dependent on the genetics of the pig; however, confirming this observation will require experiments designed specifically for this question.

Technical Abstract: Porcine circovirus type 2 (PCV2) is an important pathogen in the porcine respiratory disease complex (PRDC) and its persistence may be due to dysregulation of systemic immunity. We examined this contention using isolator piglets. We present data on Ig levels in serum and bronchio-alveolar lavage (BAL), on antibody response to PCV2 and to TNP conjugates used as model antigens in 48 PCV2-infected isolator piglets. We compared these to data from TNP-immunized isolator piglets colonized with a probiotic flora, those infected with swine influenza (S-FLU) and those infected with porcine respiratory and reproductive syndrome virus (PRRSV). We found that PCV2 infection does not cause generalized hypergammaglobulinemia that characterizes PRRSV infections, but causes an unexplained increase in serum IgA. All animals had serum IgG to the ORF2 gene product of PCR2, but neither IgA nor IgG anti-ORF2 responses in BAL. PCV2 infection is a poor adjuvant since only natural anti-TNP antibodies were found. Unexpectedly, immunization appeared to result in lower Ig levels and lower anti-ORF2 responses. There was extreme variation in serum Ig levels in response to infection that could in part be traced to genetic and gender differences. These data suggest that non-replicating vaccines are unlikely to result in a significant antibody response but may be protective by priming the system. In any case, developers may have to contend with significant genetic differences in the response of piglets to PCV2.