Anette Baumer for providing the PCV2 primers and probe, and help with the TaqMan real time PCR. == NG25 References ==. secreting cells (SC) that were not specific for PCV2 were detected by ELISPOT assay at day 7 p.i. Interestingly, this response was absent in the PCV2/PPV dual infected animals. PCV2-specific IFN- SC were observed in the PCV2/PPV infected group at 7 d p.i. and in the PCV2 single infected group at 21 NG25 d p.i. A reduction in the numbers of IFN- SC was observed following anti-CD4 and anti-CD8 antibody treatment, suggesting roles for both CD4+and CD8+T cells in the response against PCV2 infection. This was supported by an observed increase in the percentage of IFN- positive CD8hicytotoxic T cells as well NG25 as IFN- positive CD8-/lowhelper T cells after PCV2in vitrore-stimulation. == Conclusions == Infection of weaned SPF piglets with PCV2 alone or combined with PPV does not induce disease and in both cases a relatively slow anti-PCV2 antibody response and weak T lymphocyte responses were found. Knowledge on such immunological characteristics is important for both PCV2 pathogenesis and vaccination. == Background == NG25 Porcine circovirus type 2 (PCV2) is a non-enveloped, circular single stranded DNA virus belonging to the Circoviridiae virus family [1], and is the causative agent of a number of diseases in swine, particularly postweaning multisystemic wasting syndrome (PMWS) [2]. The genome of PCV2 is 1759 nucleotides long, making it one of the smallest viruses replicating autonomously in mammalian cells [3]. PCV2 was first isolated from tissues of PMWS diseased pigs in Canada [4], the US and Europe [5] in 1998. Disease has been reproduced by viral co-infection of colostrum-deprived or gnotobiotic piglets with PCV2 and porcine parvovirus (PPV) [6,7]. Particular vaccine adjuvant administration has also been shown to assist development of PMWS disease after experimental PCV2 infection [8,9]. Nevertheless, PCV2 is clearly the primary causative agent of PMWS [10], requiring the secondary factors such as co-infections or vaccinations for Mouse monoclonal to Cytokeratin 19 full expression of the disease. It is assumed that secondary viral infections or the administration of immunostimulatory compounds activate PCV2 infected cells to divide [9], thus promoting the replicative cycle of PCV2, which is dependent on the host DNA polymerase [11]. Nevertheless, neither natural nor experimental PCV2 infection together with cofactors will induce disease in all infected animals. On the farm, PCV2-induced diseases have been found to increase the pig mortality rate from 2-3% to 14-30%. NG25 PMWS-diseased animals are most often in the age range of 8-12 weeks old. They display clinical symptoms of wasting, diarrhoea, jaundice, respiratory distress and enlarged lymph nodes [12]. Typical histological findings are also reported in lymph nodes: The follicular architecture is lost, lymphocytes are depleted, histiocytes and multinucleated giant cells infiltrate the lymph nodes, and basophilic inclusion bodies are detected in the histiocytes [13]. In addition, interstitial pneumonia, mononuclear inflammatory infiltration in the liver, lymphoplasmacytic colitis and peri-endarteritis are observed [14,15]. The induction of anti-PCV2 neutralizing antibodies (Ab) was shown to correlate with protection from disease [16]. While important, Ab are effective at targeting extracellular virus and cell surface antigen (Ag) only. PCV2 has been shown to infect epithelial, endothelial and monocytic cellsin vivo[14,15,17,18], andin vitroobservations on primary cells have confirmed that this reflects replicating virus [19-22]. Considering that PCV2 is a non-enveloped virus, its capsid protein is unlikely to be expressed at the surface of infected cells; indeed, there is no evidence that this occurs. Accordingly, virion proteins could not represent a target for Ab-mediated immune defence against PCV2-infected cells; other cytotoxic mechanisms would be required. While natural killer cells and the cytotoxic T lymphocyte (CTLs)-based immune defences are strong candidates for eradicating PCV2-infected cells, there have been no studies characterizing the existence of PCV2-specific T cell responses – neither CTLs nor T helper.