Enhancing mucosal immunity in mice by recombinant adenovirus expressing major epitopes of porcine circovirus-2 capsid protein delivered with cytosine-phosphate-guanosine oligodeoxynucleotides

A recombinant replication-defective adenovirus expressing the major epitopes of porcine circovirus-2 (PCV-2) capsid protein (rAd/Cap/518) was previously constructed and shown to induce mucosal immunity in mice following intranasal delivery. In the present study, immune responses induced by intranasal immunization with a combination of rAd/Cap/518 and cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODN) were evaluated in mice. The levels of PCV-2-specific IgG in serum and IgA in saliva, lung, and intestinal fluids were significantly higher in the group immunized with rAd/Cap/518 and CpG ODN than animals immunized with rAd/Cap/518 alone. The frequencies of IL-2-secreting CD4+ T cells and IFN-gamma-producing CD8+ T cells were significantly higher in the combined immunization group than mice immunized with rAd/Cap/518 alone. The frequencies of CD3+, CD3+CD4+CD8-, and CD3+CD4-CD8+ T cells in the combined immunization group were similar to that treated with CpG ODN alone, but significantly higher than mice that did not receive CpG ODN. PCV-2 load after challenge in the combined immunization group was significantly lower than that in the phosphate-buffered saline placebo group and approximately 7-fold lower in the group treated with CpG ODN alone. These results indicate that rAd/Cap/518 combined with CpG ODN can enhance systemic and local mucosal immunity in mice, and represent a promising synergetic mucosal vaccine against PCV-2.

Distribution and characterization of IL-10-secreting cells in lymphoid tissues of PCV2-infected pigs

Distribution and characterization of interlukin-10 (IL-10)-secreting cells in lymphoid tissues of pigs naturally infected with porcine circovirus type 2 (PCV2) were evaluated in accordance with PCV2 antigen detection. After screening a total of 56 pigs showing the symptoms of postweaning multisystemic wasting syndrome (PMWS), 15 pigs were PCV2 positive and 5 pigs, which showed stronger positive signals over multiples tissues were further investigated. This study showed that in PCV2-infected lymphoid tissues, particularly mandibular lymph node, spleen and tonsil, IL-10 expression was mainly localized in T-cell rich areas but rarely in B cell rich areas. IL-10 was highly expressed in bystander cells but rarely in PCV2-infected cells. Elevated IL-10 expression was predominantly associated with T cells, but rarely with B cells or with macrophages. The results of this study provide evidence for the role of IL-10 in chronic PCV2 infection and its relation to PCV2 antigen in affected tissues. Constantly elevated levels of IL-10 lead to immunosuppression in persistent and chronic viral infections. The increased IL-10 expression observed in PCV2 infection in this study suggests that IL-10-mediated immunosuppression may play an important role in the pathogenesis and maintenance of naturally occurring PCV2 infection.