Abstract
Porcine circovirus type 2 (PCV2) is the primary pathogen of porcine circovirus diseases and porcine circovirus associated diseases. Immunization with a vaccine is considered an effective measure to control these diseases. However, it is still unknown whether PCV2 vaccines have protective immune responses on the animals infected with swine influenza virus (SIV), a pandemic virus in swine herds. In this study, we first compared the effects of 2 different PCV2 vaccines on normal mice and SIV-infected mice, respectively. The results showed that these two vaccines had protective immune responses in normal mice, and the subunit vaccine (vaccine S) had better effects. However, the inactivated vaccine (vaccine I) instead of vaccine S exhibited more immune responses in the SIV-infected mice. SIV infection significantly decreased the immune responses of vaccine S in varying aspects including decreased PCV2 antibody levels and increased PCV2 replication. Mechanistically, further studies showed that SIV infection increased IL-10 expression and M2 macrophage percentage, but decreased TNF-α expression and M1 macrophage percentage in the mice immunized with vaccine S; on the contrary, macrophage depleting by using clodronate-containing liposomes significantly alleviated the SIV infection-induced decrease in the protective immune responses of vaccine S against PCV2. This study indicates that SIV infection decreases the protective immune responses of vaccine S against PCV2. The macrophage polarization induced by SIV infection might facilitate decreased immune responses to vaccine S, which provides new insight into vaccine evaluation and a reference for the analysis of immunization failure.
Highlights
Porcine circovirus type 2 (PCV2) belongs to the Circoviridae family and is a single-standard circular DNA virus
To explore the immune responses of different PCV2 vaccines on normal animals, mice were treated with subunit vaccine and inactivated vaccine, respectively, and challenged by PCV2 at 21 days post-immunization (Figure 1A)
The results showed that weight gain, thymus index, and anti-PCV2 antibody titers significantly increased after macrophage depletion, while PCV2 replication markedly decreased as demonstrated by decreased PCV2 DNA copies and histochemistry score (H-score)
Summary
Porcine circovirus type 2 (PCV2) belongs to the Circoviridae family and is a single-standard circular DNA virus. SIV Weakens PCV2 Subunit Vaccine (Chae, 2005; Baekbo et al, 2012). PCV2 has been proven to be immunosuppressive, which increases the risk of the host infecting other pathogens (Segalés, 2012). It is valuable to utilize effective measures to control the PCV2 infection in pigs. Vaccination has been always considered one of the most efficient methods of preventing PCV2 infection in pigs. The potential infection of other pathogens has always existed in swine herds and is likely to weaken immune responses to PCV2 vaccines. SIV infection may increase PCV2 infection via inducing immunosuppression, but this has not been reported to date
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