Comparison of Immunogold Silver Staining (IGSS) with Two Immunoperoxidase Staining Systems for the Detection of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Antigens in Formalin-Fixed Tissues

Abstract

Laboratory diagnosis of porcine reproductive and respiratory syndrome (PRRS), a newly identified and economically important viral disease of swine, is based on the combination of serology, histopathology, and virus isolation. The isolation and identification of PRRS virus (PRRSV) is complex and labor intensive and may require many days or weeks to perform. The histological diagnosis of infection by PRRSV is limited since other viral pathogens may induce similar lesions. Furthermore, secondary bacterial infection commonly associated with PRRSV infection can complicate the interpretation of lesions. Detection of viral antigens in frozen lung sections using immunofluorescence (IF) has been reported, 1,11 but the IF procedure has shortcomings. The use of immunohistoch emical methods for the detection of viral antigens in formalin-fixe d paraffin-embed ded tissues offers several advantages over the IF technique. These procedures allow direct visualization of viral antigens along with simultaneous evaluation of histological lesions in the affected tissue using an ordinary light microscope. The ability to detect viral antigens in routinely fixed tissues facilitates convenient collection and transport of specimens, and potentially infectious specimens can be handled safely. Finally, since antigens are usually stable indefinitely in paraffin-embedded tissues, retrospective diagnoses can be made. The immunogold silver staining (IGSS) is an indirect 2-step nonenzyme-based method in which the secondary antibody labeled with colloidal gold particles is visualized following a silver precipitation reaction . 4