Effects of porcine circovirus type 2 on expression of mRNA associated with endogenous antigen processing and presentation in pulmonary alveolar macrophages and circulating T lymphocytes in piglets

Pulmonary alveolar macrophages (PAMs) are the major target cells of porcine circovirus type 2 (PCV2). This study examined cellular immunity and expression of molecules associated with endogenous antigen processing and presentation in porcine PAMs for 28 days following infection with PCV2. The numbers of total T cells and T lymphocyte subpopulations were measured by flow cytometry (FCM). The expression of mRNA of large multifunctional peptidase 7 (LMP7), ubiquitin-specific protease (UBP), heat shock proteins 70 and 90 (HSP70 and HSP90), major histocompatibility class I (MHC-I), β2-microglobulin, glucose-regulated protein 94 (GRP94), calnexin and calreticulin of PAMs from PCV2 infected and control pigs were determined by real-time reverse transcriptase PCR. The absolute numbers of total T cells, T helper (Th) cells, cytotoxic T cells and γδ T cells, but not memory/activated Th cells, decreased following PCV2 infection. There was decreased expression of LMP7 mRNA at 3 days postinfection (DPI), whereas expression of UBP and calreticulin mRNA was increased at 3 DPI, expression of HSP90 and β2-microglobulin mRNA was increased at 3 and 7 DPI and expression of GRP94 mRNA was increased at 14 DPI. PAMs from PCV2-infected piglets had lower surface expression of CD80/CD86 at 7 and 14 DPI and MHC-II at 7 DPI. These findings suggest that there are alterations in cellular immune function and in the endogenous antigen presentation capacity of PAMs in PCV2-infected piglets.