Effects of dexamethasone on the pathogenesis of porcine circovirus type 2 infection in piglets.

To investigate the effect of immunosuppression on porcine circovirus type 2 (PCV2) infection, hysterectomy-produced, colostrum-deprived piglets were inoculated with the virus by the intranasal or intraperitoneal route, with or without dexamethasone (DEX) treatment. Eleven piglets aged 8 days were divided into four groups, namely group A (four animals given PCV2), B (three given PCV2 with DEX), C (two given sterile medium with DEX) and D (two given sterile medium). No significant clinical signs were observed. Histopathological and immunohistochemical examination revealed granulomatous inflammation and PCV2 antigen in the lymphoid tissues of group B piglets, but not in the other three groups. Flow cytometric analysis of peripheral blood lymphocytes showed a reduced number of CD4+ T cells in DEX-treated piglets (groups A and C). No differences between groups were observed in respect of the number of B cells, serum IgG concentration, or PCV2 antibody titre. These results indicate that DEX influenced the pathogenic effects of PCV2 infection in lymphoid organs, and that suppression of cell-mediated immunity may play a role in the aetiology of postweaning multisystemic wasting syndrome.