Porcine reproductive and respiratory syndrome virus (PRRSV) has disrupted the global swine industry since the 1980s. PRRSV-host interactions are largely still unknown but may involve host ISG15 protein. In this study, we developed a monoclonal antibody (Mab-3D5E6) specific for swine ISG15 (sISG15) by immunizing mice with recombinant sISG15. A sandwich enzyme-linked immunosorbent assay (ELISA) incorporating this sISG15-specific Mab was developed to detect sISG15 and provided a lower limit of sISG15 detection of 200 pg/mL. ELISA results demonstrated that infection of porcine alveolar macrophages (PAMs) with low-virulence or attenuated PRRSV vaccine strains induced intracellular ISG15 expression that was independe... More
Porcine reproductive and respiratory syndrome virus (PRRSV) has disrupted the global swine industry since the 1980s. PRRSV-host interactions are largely still unknown but may involve host ISG15 protein. In this study, we developed a monoclonal antibody (Mab-3D5E6) specific for swine ISG15 (sISG15) by immunizing mice with recombinant sISG15. A sandwich enzyme-linked immunosorbent assay (ELISA) incorporating this sISG15-specific Mab was developed to detect sISG15 and provided a lower limit of sISG15 detection of 200 pg/mL. ELISA results demonstrated that infection of porcine alveolar macrophages (PAMs) with low-virulence or attenuated PRRSV vaccine strains induced intracellular ISG15 expression that was independent of type I IFN production, while PAMs infection with a PRRSV vaccine strain promoted extracellular ISG15 secretion from infected PAMs. Conversely, the addition of recombinant sISG15 to PAMs mimicked natural extracellular ISG15 effects whereby sISG15 functioned as a cytokine by activating PAMs. Once activated, PAMs could inhibit PRRSV replication and resist infection with PRRSV vaccine strain TJM. In summary, a sandwich ELISA incorporating homemade anti-ISG15 Mab detected ISG15 secretion induced by PAMs infection with a PRRSV vaccine strain. Recombinant ISG15 added to cells exhibited cytokine-like activity that stimulated PAMs to assume an anti-viral state that enabled them to inhibit PRRSV replication and resist viral infection.
