The elimination of infected cells by cytotoxic T lymphocytes (CTLs) occurs through interactions between
T cell receptors (TCRs) and pathogen-derived antigenic
peptide-major histocompatibility complex (MHC) class I complexes. The immunoproteasome (i-
proteasome), which is a large proteolytic machine derived from the constitutive
proteasome, is highly efficient at processing
antigens for presentation on
MHC class I molecules to activate CD8+ T lymphocytes; this in turn facilitates
antiviral adaptive immune responses. To date, i-
proteasome expression in the porcine lung has not been investigated. In this study, we systematically analyzed the expression of the i-
proteasome in vivo in the porcine lung and in vitro in alveolar macrophages (AMs) under normal and inflammatory conditions such as with IFN-γ stimulation or PRRSV
infection. AMs were shown to readily express low levels of i-
proteasome subunits, which were confined to the cytoplasm and nucleus under normal conditions. While i-
proteasome expression could also be detected in other lung parenchymal cells including alveolar type I and II cells and bronchial epithelial cells during inflammatory conditions. Results showed that i-
proteasome expression is markedly increased in IFN-γ-stimulated AMs and PRRSV-infected lung tissue. In addition, PRRSV
infection promoted i-
proteasome expression in AMs during the early stage of
infection, and this was independent of IFN-γ; expression was attenuated during the later stage of
infection in vitro. These results suggested that i-
proteasome subunit expression can be induced in the porcine lung, which facilitates the development of
antiviral adaptive immune responses against intracellular
infections. These results could facilitate the development of
therapeutics that target intracellular pathogens.