Porcine circovirus type 2 stimulates plasmacytoid dendritic cells in the presence of IFN-gamma

Porcine circovirus type 2 (PCV2) is recognized as the primary cause for the development of porcine circovirus-associated disease (PCVD). A number of reports demonstrated that PCV2 double-stranded (ds) DNA inhibits interferon-α (IFN-α) production in cultures of porcine plasmacytoid dendritic cells (pDC). In addition, a short-lived peak of systemic IFN-α was detectable in the serum of PCV2-infected pigs, suggesting that the interaction of PCV2 with pDC may be more complex. Culturing pDC supplemented with IFN-γ actually rendered the cells responsive to the presence of PCV2. Accordingly, viral genomic single-stranded (ss) and replicative dsDNA forms have been examined for their ability to activate pDC. It was noted that the encapsulated viral ssDNA stimulated pDC in the presence of IFN-γ; free viral DNA, presumably as double-stranded forms, was responsible for inhibiting pDC responses, even in the presence of the several cytokines known to promote pDC responses. These data suggest that the equilibrium between the levels of encapsulated genomic ssDNA and free dsDNA replicative forms of PCV2 is determinant in defining the immunomodulatory characteristics of the virus infection.